2012 Cell Day Online Chat Transcript

The 2012 NIGMS Cell Day chat was held on Friday, November 2, 2012 from 10 a.m. to 3 p.m. EDT. Scientists from across the Institute answered questions from students, teachers and the general public.

Moderator: Happy Cell Day! The chatroom is now open, and our experts eagerly await your questions!

How much research is being done on Creutzfeld-Jakob Disease (CJD) at NIH?
Donna Krasnewich, M.D., Ph.D.: Research funding to NIH provides support for research both on NIH campus and in the extramural community which are academic institutions across the United States. One place to look for information about clinical studies is at www.clinicaltrials.gov. A good site to look for information about Creutzfeld-Jakob Disease is GeneTests, www.genetests.org, the link to this specific disorder.
Fauquier H.S. in VA (12th grade student)

Are you concerned about the presidential election regarding stem cell research??
Judith Greenberg, Ph.D.: NIGMS is involved in many kinds of stem cell research including induced pluripotent stem cell research, adult stem cell research and studies using animal models. Regardless of the outcome of the election, stem cell research will remain an important part of NIH research.
McKeesport High School in PA (10th grade teacher)

Which experts are present here? We would like to know in order to best direct our questions.
John Laffan, Ph.D.: We will have a variety of experts in all day. Currently we have: Dr. Wehrle Dr. Krasnewich Dr. Pike Dr. Bender Dr. Smith Dr. Laffan there are mini resumes for all of our experts on our site.
Piney Grove Middle School in GA (7th grade teacher)

How many cells are there in the body?
John Laffan, Ph.D.: There are approximately 10 to the 13th human cells in your body. Interestingly, a healthy person also has 10 to the 14th (10x more) bacteria on the same body. The bacteria are just so much smaller that they have much less volume.
Parent (T. Bailey Lash) in MD

How do viruses get into cells?
Janna Wehrle, Ph.D.: First a virus binds to the outside of a cell. Often viruses use the very same docking sites that the cell uses to pick up normal, healthy materials. When the cell runs its "import" process, it takes the virus inside, instead.
Emerson Junior High in CA (7th grade student)

Do all cells have the same structure?
Ward Smith, Ph.D.: No. Different cells have different functions and different sizes and shapes. For example, red blood cells are round in the normal state while nerve cells are very elongated. Some bacterial cells have flagella for movement, some cells are large (such as mammalian egg cells) and others are much smaller (such as sperm cells).
Emerson Junior High in CA (7th grade student)

If detectives found my DNA at a crime scene, would it be inside my cells?
John Laffan, Ph.D.: Yes, mostly. You shed tiny cells all the time, they have your unique DNA in each one. Free DNA is very sticky and easily degrades so it is difficult to recover DNA not inside cells.
Emerson Junior High in CA (7th grade student)

Are our cells identical to our biological parents' cells?
Janna Wehrle, Ph.D.: Your cells won't be exactly identical to those of your biological parents, because they contain some genes from each of them. You're unique! Unless you have an identical twin. Only identical twins have cells with exactly the same genes.
Mapletown Jr./Sr. High School in PA (12th grade student)

How many cells are in a plant?
Brian Pike, Ph.D.: Great question! Thanks for asking. Because plants can vary greatly in size, some plants may only have a few cells while other plants can have billions of cells. For example, a large oak tree may have billions of cells while a small flower would have far fewer.
Mapletown Jr./Sr. High School in PA (9th grade student)

Knock knock. Whos there? CELLS! Cells who? Its cell day woooooooo! :D
Joe Gindhart, Ph.D.: Thank you for your interest in cell day!
Mapletown Jr./Sr. High School in PA (10th grade student)

Why do animal cells not have a cell wall?
Janna Wehrle, Ph.D.: Very very long ago in evolution some cells survived better with cell walls and others changed to survive without them. The cells that survived without cell walls found other ways to deal with the stresses of their surroundings. Starting there each group followed a separate evolutionary path.
Mapletown Jr./Sr. High School in PA (10th grade student)

What led you into a career in cellular biology? (What first interested you?)
Joe Gindhart, Ph.D.: Biology was my favorite subject in high school. I studied biology in college and then did genetics research. My interest in cell biology came from my interest in watching things move in cells. I studied motor proteins in fruit flies for many years before I began working at NIGMS.
Piney Grove Middle School in GA (7th grade student)

How many lysosomes are in a cell?
Michael Bender, Ph.D.: The number of lysosomes is one of the many things that's different for every cell type. It depends on what the cell's function is.
Penn State in PA (12th grade student)

What kinds of jobs are up and coming in cellular biology?
Michael Bender, Ph.D.: There are a lot of good jobs in cellular biology. Universities have many scientists at all levels working to understand how cells function. Biotechnology and pharmaceutical companies make use of this basic research to carry out research focused on discovering new medicines and treatments for disease. A good background in biology, chemistry, or math can prepare you well for these positions.
Mapletown Jr./Sr. High School in PA (teacher)

Does a leaf bug have plant cells, animal cells, or a combination?
Brian Pike, Ph.D.: Good question! While a leaf bug might look like a plant, it is an insect and is only made of insect cells. Except of course when it eats a leaf, then it would have plant cells in its stomach (just like you would when you eat a leaf of lettuce)! But when you or an insect eats a plant, the plant cells are broken down in the stomach and used for nutrition for building animals cells.
Piney Grove Middle School in GA (7th grade student)

The material that the cell "cleans" out of itself where does it go? and what the waste material do after it is not needed?
Donna Krasnewich, M.D., Ph.D.: Inside of your cells are organelles called lysosomes. Their job is to break down proteins, and sugars in the cell when they are no longer needed. Proteins called proteases and glycosidases are the tools the cells use to break down these proteins into amino acids and sugar chains into individuals sugars. Then the lysosome transports these pools of building block compounds, amino acids and sugars, back into the cytoplasm to be recycled into the synthesizing pathway of new proteins and oligosaccharides ( multiple sugar chains). This makes the cells more efficient because they don't have to build these smaller structures. There are a group of disorders called "lysosomal storage disorders" where affected individuals have a protease or glycosidase that doesn't work well. In those individuals the lysosomes store undigested large proteins or oligosaccharides and the cells struggle at their jobs.
Mapletown Jr./Sr. High School in PA (12th grade student)

How many cells could I fit in my mouth?
John Laffan, Ph.D.: It depends. An egg is a single cell. It would be hard to fit more than a few of those in your mouth at once. Most eukaryote cells are much smaller, so you can fit billions of plant cells in your mouth easily. And bacterial cells are even smaller so you could fit hundred and thousands of billions of bacterial cells in your mouth at once (though it may not taste particularly good).
Sidwell Friends High School in DC (12th grade)

What is a Somatic Cell nuclear transplant.?
Janna Wehrle, Ph.D.: Somatic cell nuclear transplant is a procedure in which a scientists removes the nucleus from one cell and puts them into a different cell, which had its nucleus removed. Because all the genes are in the nucleus, this permanently changes the cell.
Mapletown Jr./Sr. High School in PA (10th grade student)

What is your favorite cell?
Joe Gindhart, Ph.D.: My favorite cell is the neuron. Neurons have many different shapes and sizes; some are over three feet long! Neurons are essential for thinking and all our senses. We know a lot about how neurons work, but I think we are just seeing the tip of the iceberg regarding our understanding of the senses, how we think, and how nerve cells respond to drugs.
Sidwell Friends High School in DC (12th grade)

Can you discuss HeLa cells and why they are so special?
Ward Smith, Ph.D.: HeLa cells are a line of human cancer cells derived from one person, Henrietta Lacks. These cells are immortal meaning that they can be grown over and over without the cells dying. This ability to use one line of cells in research laboratories across the world has been very beneficial to medical research.
N/A in MD

What would happen if all my cells fell off?
Michael Bender, Ph.D.: You wouldn't want all your cells to fall off but it turns out that we lose lots of cells every day from our skin and our gut (likely millions a day). Happily, your body makes lots of new cells every day from adult stem cells in most tissues.
Sidwell Friends High School in DC (12th grade)

What are those letters in your Cell Day logo made up of? I can't quite make them out. Looks like worms and stuff.
John Laffan, Ph.D.: They are some of the organelles taken from our picture on the site.​
David in FL

Approximately how small are cells?
Brian Pike, Ph.D.: There are many cell types in the human body that make up the various organs and these can vary greatly in size. For example there are trillions of cells in the human body and over 200 major cell types. Most cells are too small to be seen with the naked eye and must be viewed through a microscope. The largest human cell in diameter (across) is the egg cell, which can just barely be seen with the naked eye. Some of the longest cells in the body are nerve cells. Some nerve cells in your spine can be over 3 feet long as they send their projections from your spine all the way down to your toes.
Piney Grove Middle School in GA (7th grade student)

How do they take a fat stem cell and turn it into a nerve cell?
Judith Greenberg, Ph.D.: Scientists can transform fat (adipose) cells into induced pluripotent stem cells (iPS), which can then differentiate into many cell types, including nerve cells (neurons).
Mapletown Jr./Sr. High School in PA (9th grade student)

How far into a family's history to genes go?
Michael Bender, Ph.D.: You can track your genes a long way back in history. For example, DNA evidence has been used to show a genetic link between Thomas Jefferson and Sally Hemings.
Piney Grove Middle School in GA (7th grade student)

What is the source of embryos used for making embryonic stem cells?
Judith Greenberg, Ph.D.: Embryonic stem cells, as their name suggests, are derived from embryos. Most embryonic stem cells are derived from embryos that develop from eggs that have been fertilized in vitro in an in vitro fertilization clinic, and then donated for research purposes with informed consent of the donors. They are not derived from eggs fertilized in a woman's body. For more information, see the NIH Stem Cell Information page at http://stemcells.nih.gov.
Mapletown Jr./Sr. High School in PA (10th grade student)

Is it possible for a animal cell to "spring a leak"? and if so how would they repair themselves?
Ward Smith, Ph.D.: Interesting question. Cells need to regulate the passage of molecules into and out of the cell. This process is normally under tight control, however there can be circumstances which cause the cell to become "leaky" e.g. disruption of the balance in the concentration of molecules inside and outside the cell. Some of these problems can be corrected by the cell but too much leakage is fatal.
Mapletown Jr./Sr. High School in PA (student)

What is osmosis?
Janna Wehrle, Ph.D.: Osmosis is important for cells, because their membranes allow only certain compounds to cross. But water passes easily. If any one chemical is at a higher concentration on one side, it creates a force that drives the water to the side with the higher concentration. That's osmosis. It can make the cell shrink or swell, so it's important to control.
Piney Grove Middle School in GA (7th grade student)

is it possible for there to be an instance where a cell can not divide and multiply ?
Michael Bender, Ph.D.: Yes, mature forms of neurons, red blood cells and muscle cells don't divide. Interestingly, cells also have normal controls on division that can temporarily prevent them from dividing, for example if their DNA has been damaged.
Mapletown Jr./Sr. High School in PA (10th grade student)

What if a cell was missing an organelle?
Joe Gindhart, Ph.D.: Well, it depends on which organelle and which cell type. Some diseases, such as lysosomal storage diseases and mitochondrial disorders, are caused by defects in specific organelles. However, other cell types lack an organelle as part of their normal structure, such as how red blood cells lack a nucleus.
Mapletown Jr./Sr. High School in PA (10th grade student)

If cells make up us, what makes up cells?
Joe Gindhart, Ph.D.: Cells are made of organic molecules, such as lipids, carbohydrates, nucleotides, and amino acids. The cell uses chemical energy to make polymers of these molecules, for example to make DNA and RNA strands from nucleotides and proteins from amino acids. Cells also contain inorganic molecules such as salt and metals in small amounts, and lots of water, too.
Piney Grove Middle School in GA (7th grade student)

Where is the DNA located within a cell?
Ward Smith, Ph.D.: DNA can be found in the in chromosomes in the nucleus of eukaryotic cells. DNA also can be found in mitochondria in the cell of higher organisms. Bacteria and viruses do not contain these organelles, r​ather the DNA exists free in these organisms.
David in FL

In cloning (such as the sheep Dolly) has any more scientific cellular cloning taken place? and if so where they successful and can this benefit the medical field by building new organs (such as a heart)?
John Laffan, Ph.D.: Dozens of different animals have been successfully cloned (not humans). They have all been very informative scientifically. There are several different approaches being investigated now to try to make new organs. Therapeutic cloning is one of those approaches. They are not trying to clone the whole animal in that case, just create an pluripotent cells which can be directed to become the appropriate organ (this is still a ways off).
Mapletown Jr./Sr. High School in PA (student)

Does lysosome malfunction play a role in diseases such as dementia?
Donna Krasnewich, M.D., Ph.D.: The first thing to remember is that dementia, memory loss, is a symptom of many different disorders including the most common, Alzheimer's disease. In Alzheimer's disease there is a build up of amyloid proteins in the brain. Current research is working to understand what leads to this "plaque" formation. It is clear that this plaque formation leads to neuron cell death. Some think that amyloid buildup changes calcium levels in the cell leading to "apoptosis", or programmed cell death. There are other proposed mechanisms as well. With that said, there is some evidence that rarer forms of neurodegenerative disorders may be accelerated by abnormal lysosome function. For example, individuals who have the lysosomal storage disorder, Gaucher disease, have a small but increased risk of parkinson symptoms. This clinical observation suggests a link between neurodegenerative disorders and lysosomal function. The research is ongoing. Thank you for this very interesting question.
McKeesport High School in PA (10th grade teacher)

Moderator: Keep the questions coming!

W​​​​hat long term affects can stem cell research have on artifici​ally producing organs for donation?
Doug Sheeley, Sc.D.: This is a great question. One of the hard things about organ donation, including the stem cells that are used in bone marrow transplants, is matching organs between donors and recipients. There are a lot of signaling molecules on the surfaces of cells that help our cells recognize each other, so our immune system can tell the difference between "us" and invading organisms like bacteria. When an organ or tissue is transplanted into a different person, even when doctors try hard to make sure those molecules match, often the recipient's body mistakenly attacks the new tissue. If we could make tissues and organs from stem cells taken from the person who needs the organ, it will look like their own body, and they won't attack it. Even if we can make organs from someone else's stem cells, it might slip under the radar, so to speak, and be more likely to be accepted. This would help save a lot of lives. There are scientists and doctors working on this. In the meantime, we all need to remember that there are many people waiting for organ and tissue donations. Signing up to be a potential bone marrow donor, or checking organ donor "yes" on our driver's license is a great idea.
Rockdale Magnet School in HI (11th grade student)

Do my cells think?
Janna Wehrle, Ph.D.: Individual cells don't "think" in the way our complete brains think. Individual cells do react to their surroundings and change their behaviors according to programs set up in their genes, but that's not really thinking. That requires the complex and specially organized function of hundreds of billions of nerve cells in in brain.
Sidwell Friends High School in DC (12th grade)

How long does it take for the cell cycle to happen ?
Joe Gindhart, Ph.D.: The cell cycle varies depending on the organism, stage of development, and the conditions in the environment outside the cell. Human cells typically need about 24 hours to divide, but E. coli cells can divide in 20 minutes. Cells in the fertilized fruit fly egg divide every 8 minutes, but cells in the larva and adult take much longer to divide. E. coli growing in rich nutrient conditions divide quickly, but they divide much more slowly under crowded conditions or when nutrients are limited.
Montgomery Middle School in CA (7th grade student)

How long do cells live?
Doug Sheeley, Sc.D.: Well, that depends. (Don't you hate it when adults begin answers to simple questions that way?) For example, in your body, there are a lot of different kinds of cells. They do different jobs, and they last for different lengths of time. Some cells are only around for a very short time. Platelets aren't really complete cells, but they only last for a few days. The cells that line your digestive system turn over very rapidly. Brain cells last a very long time. In fact, for a long time, scientists thought that once our brain finished growing, the cells we start with are the only ones we'll ever have. Over the past few years, scientists have figured out that brain cells do get replaced. This has changed the way we think about the potential of the brain to recover from some kinds of injuries or illnesses. The length of time that cells last, and the things that kill them or make them even "self-destruct" at the right time, depend on the kind of cell and the situation they're in. Thanks for asking.
Montgomery Middle School in CA (7th grade student)

What happens if the chromosomes get stuck together in metaphase?
Donna Krasnewich, M.D., Ph.D.: In humans, there are 23 pairs of chromosomes in each of our cells. In metaphase, chromosomes pair up with each other. For example, chromosome 1 pairs up with chromosome 1. Then in anaphase, as the cell continues on the path to cell division, the chromosome pairs split. If the chromosome pairs do not split correctly, then one of the cells will have an abnormal number of chromosomes after cell division is complete. In many cases, having less or more than the normal number of chromosomes makes the cell function abnormally.
Montgomery Middle School in CA (7th grade teacher)

How does a cell know when to do the cell cycle?
Joe Gindhart, Ph.D.: The cell cycle has four stages: G1, S, G2, and M. There are cellular "checkpoints" at the end of G1 and G2 that indirectly measure cell size, nutrient conditions, whether DNA is replicated properly, and signals from neighboring cells. The cell transitions from G1 to S when nutrient and signaling conditions are "right", and from G2 to M when DNA is fully replicated and signaling conditions are ready to go. Cells with mutations in these checkpoints can cause the cell to divide uncontrollably, as is sometimes seen in patients with cancer.
Montgomery Middle School in CA (7th grade student)

Why does DNA mutate within the cells?
John Laffan, Ph.D.: There are lots of mutagenic substances which increase the rate of mutation (like cigarette smoke). But even perfect cells get mutations. Each of your cell has about 6.4 billion base pairs of DNA. To make another cell this has to be duplicated completely. The replication machinery is very accurate but even if it only made 1 mistake in a billion the next generation cell would have 6-7 mistakes (it is actually a little better than that). Imagine that the only way to pass a test is to miss less than one question in a billion.
McKeesport High School in PA (10th grade student)

Does a human always have 46 chromosomes or do they have less when they are born?
Janna Wehrle, Ph.D.: The number of chromosomes you have is already set before you're born, and doesn't change during your life. Almost everyone is born with 46 chromosomes, which is good because having too many or too few chromosomes leads to diseases.
Montgomery Middle School in CA (7th grade student)

How long does it take for one cell to make a whole organism?
Doug Sheeley, Sc.D.: That's a pretty interesting question, and kind of a hard one to answer. After all, if we only think about mammals, we know that the gestation period- how long a mother is pregnant- varies a lot among species. Mice are born after about 3 weeks, but elephants take over a year. If you think about species that are a lot simpler, or that develop differently, it gets more complicated, and can take a really short time. For example, emerging from an egg (like an insect or a frog or a bird) and maybe going through different phases of development, can happen quickly or take months. At what point does a single cell become a butterfly- when the caterpillar emerges or when a butterfly breaks out of a cocoon? There are a lot of things that have to happen for a single cell to become a whole animal. That cell has to divide, and that process has to keep going for a long time, while the cells that are created begin to do two things. They change into specialized cells that do different job s, and they move to different positions, forming groups of similar cells that keep dividing to develop into tissues and then organs. All that organization and growth can take a while. Of course in the case of single celled organisms like bacteria or yeast, once that cell divides, the process is complete.
Montgomery Middle School in CA (7th grade student)

Will they ever find a cure from cancer?
Brian Pike, Ph.D.: Cancer is a very complicated disease that scientists have been working on for some time. Cancer can involve many different mutations on different genes, and different organs can have their own forms of cancer. The good news is that we have made tremendous progress in treating cancer, and some promising new therapies have been developed to treat specific cancers without some of the side effects of chemotherapy. For more info on cancer, go the the NIH's National Cancer Institute website at: http://www.cancer.gov/.
McKeesport High School in PA (10th grade student)

How do sex cells function ? :)
Brian Pike, Ph.D.: Good question! Sex cells function to transmit copies of each of your parents genetic information. The male sperm and female egg carry one copy of each parents genes and unite to form complete chromosomal pairs. Thus you are mixture of each of your parents genes thanks to the human sex cells and their ability to combine genetic information.
Montgomery Middle School in CA (7th grade student)

How does meiosis work.
Joe Gindhart, Ph.D.: Meiosis is the process by which cells make gametes for sexual reproduction. Gametes have 1/2 the chromosomes (haploid) of somatic cells, which are diploid. During Meiosis I, cell ploidy is reduced by half and genetic recombination occurs. During Meiosis II, the chromosomes are divided equally into gametes. The final result of Meiosis I and II is the production of four gametes. The cytoskeleton, motor proteins, chromosomes, and cytosolic proteins work together in an elegant but complicated way to make this happen. Interestingly, many of the basic mechanisms controlling meiosis in simpler organisms such as yeast are shared with higher organisms like fruit flies and us.
Montgomery Middle School in CA (7th grade student)

What chromosomes are most likely to have mutations?
Donna Krasnewich, M.D., Ph.D.: There are two things to think about here. First, each chromosome has a different number of genes, for example, chromosome 1 is a very large chromosome and is gene-rich. Also, each gene has a different mutation rate, some genes are less likely to have a mutation after replication than others. There is an interesting website to look at which diseases, caused by mutations or changes in specific genes, are linked to which chromosome. This is in the Online Mendelian Inheritance in Man, a fabulously curated list of genes and gene changes. The link to specific chromosomes, called the "Morbid Map", is http://omim.org/search/advanced/geneMap​.
Montgomery Middle School in CA (7th grade teacher)

How is stem cell research beneficial to finding a cure for cancer?
Donna Krasnewich, M.D., Ph.D.: Remember that cancer cells cause disease because they don't know how to stop dividing. Most cells have "contact inhibition" which means that they stop dividing when they come into contact with another cell. Cancer cells do not have "contact inhibition", they keep dividing and dividing, using up energy and creating big tumors. Stem cells have some similarities to some cancer cells. For example, stem cells are not well differentiated, or primitive, the same as many cancer cell. If we can understand stem cells and the pathways that control why they differentiate and divide we may better understand why cancer cells are dividing out of control and find new drugs that will stop them in their tracks. Thank you for the great question.
Piney Grove Middle School in GA (7th grade student)

What are some of the new cancer treatments that don't cause side effects?
Lee Slice, Ph.D.: That is a great question, historically because cancer cells are cells that are rapidly dividing most treatments were targeting dividing cells. These treatments interfered with DNA replication. The problem with this approach is that it also targets normal cells that are also dividing. That is why cancer patients being treated with chemotherapy lose their hair or have gastrointestinal side effects. New cancer treatments involve different targets such as modulating the immune system to specifically eliminate cancer cells or drugs that interfere with molecules within the cell that tell the cancer cell to divide. There are new approaches being studied and new clinical trials that are being developed. You can learn more at www.cancer.gov.
McKeesport High School in PA (10th grade student)

Moderator: New experts are ready for your questions: Dr. Okita, Dr. Slice, Dr. Maas, and Dr. Sheeley, in addition to Dr. Wehrle and Dr. Gindhart.

How many different types of cells are there?
John Laffan, Ph.D.: Your body contains trillions of cells, organized into more than 200 major types. Other organisms have similar distributions so there are many more different types of cells than there are different organisms. When you add bacteria to the mix (even though they are only one type each) there are billions and billions additional types.
Emerson Junior High in CA (7th grade student)

How many cells does a human have?
John Laffan, Ph.D.: There are approximately 50 billion human cells in your body. Interestingly, a healthy person also has 10x more bacterial cells on the same body. The bacteria are just so much smaller that they have much less volume.
Montgomery Middle School in CA (7th grade student)

Why do we lern About cells
Joe Gindhart, Ph.D.: When you think about the fact that you started out as a single cell, why wouldn't you want to learn about how cells divide, let you do your favorite things, contribute to disease and aid the development of treatments or cures that you one day may need! By understanding how cells work, we can better understand what happens when things go wrong.
Montgomery Middle School in CA (7th grade student)

Why do we have so many cells
Stefan Maas, Ph.D.: That is an interesting question and like many bigger questions in biology can best be understood from the perspective of evolution. The current number of cells within a particular organ, tissue or organism is the result of evolution. Therefore, the short answer to your question is: We have as many cells as we have because this has proven to be best adapted to the current environment in which we live and function. In more detail you would want to look at each organ or functional part of the body and look at why that particular component has evolved as it did.
Montgomery Middle School in CA (7th grade student)

Do humans have the same amount of chromosomes as animals?
Lee Slice, Ph.D.: The short answer is no. One of the things that differentiate species is the number of chromosomes. Humans have 23 pairs of chromosomes and mice have 40 chromosomes or 20 pairs. Great question.
Montgomery Middle School in CA (7th grade student)

Can some cells morph as other cells
Stefan Maas, Ph.D.: Certain types of cells, called stem cells, can further develop into different types of final, specialized (differentiated) cells. It depends on the environment and the needs of the body into which specialized cell type the stem cell develops. Once a cell has specialized, it usually is not able to morph into another type of cell. There are some exceptions in disease, where for example a cell that turns into a cancerous cell assumes properties that is would otherwise not have, such as being able to migrate within the body.
Montgomery Middle School in CA (7th grade student)

Why is exercise goode for your cells?
Dick Okita, Ph.D.: This is an interesting question. Exercise is good for your cells and your tissues because it helps to "train" them so they perform better. For example, muscle cells will produce their energy molecules better and lung cells will be able to use oxygen more efficiently. Exercise also is good for your health because it increases the release of molecules that will boost your body's immune system.
Smithe Jones Elementary in VA (5th grade student)

What does iterphase really do for the cell.?
Stefan Maas, Ph.D.: Interphase is a period during the cell cycle (the time period from one cell to turn into two cells). During Interphase the genetic material, the DNA, is being copied within the cell. This has to be completed before the cell can divide into two, since both daughter cells need a complete set of genes that are stored in the DNA to function. Interphase is also usually the longest phase of the cell cycle.
Montgomery Middle School in CA (7th grade student)

When do cells stop reproducing?
John Laffan, Ph.D.: Some cells stop dividing when they fully differentiate (like nerve cells) and some cell keep reproducing over your entire life (like skin cells). The trick is that the ends of the DNA have trouble replicating. There are specialized structures called telomeres at the ends of the chromosomes which help with this problem. The telomeres get smaller and smaller as the cell divides more and more. Eventually, the telomeres run out and the cell can no longer replicate.
Montgomery Middle School in CA (7th grade student)

Why have plants not evolved to be black in color in order to maximize light absorption?
Janna Wehrle, Ph.D.: Good question! Plants have different numbers of colored molecules that absorb energy to begin photosynthesis. Eventually they all have to pass energy to a single pigment, chlorophyll, to begin photosynthesis. The colors of different plants come from the mix of pigments, which is related to the light level in which the plant grows. Plants that live in low light are often nearly black. Plants that have white striped leaves, for example, only grow well in bright sunlight. But plants can get "sunburned," too, and have to protect themselves from excess sunlight. If all leaves were black, plants would need to grow mostly in the shade. The full range of leaf colors allows plants to fill all available niches.
Lexington High School in SC (12th grade student)

Can physics and chemistry help understand cells better ?
Doug Sheeley, Sc.D.: Great question. A surprising amount of research in biology and medicine is done by chemists and physicists. Cells are complex and messy, but like everything else in the world, they are made up of molecules, and those are made of atoms, of course. The principles we learn from doing physics and chemistry in other areas, like astrophysics or the petroleum industry still apply when we study biological systems like cells and organisms. There are a couple of ways physics and chemistry help us study biology. One really important way is in building complicated laboratory machines for studying cells or diagnosing diseases. For example, the MRI (magnetic resonance imaging) machines that doctors use to peer inside of us were developed from technology originally invented by physicists and then developed for use by chemists to study individual molecules. Insights from physics help scientists come up with ideas for new microscopes and other machines or "instruments" that help bio logists study what goes on in cells. Another way that chemistry and physics help us study cells is that we can learn from smaller, simpler molecules and systems how they interact, and then can apply those principles to the experiments we do on cells. For example, understanding why oily molecules stick together and how they behave in watery environments can help us understand how cell membranes work. Chemists come up with molecules that mimic ones found in nature and either help or interfere with the things they do. That is how we figure out how biological molecules work and come up with new medicines. Mathematicians get into the act too, coming up with equations that explain complex interactions between molecules and cells so we can make computer models. Biology and medicine are a great subject for all kinds of scientists to study. The things we study in math, physics and chemistry help us to understand biology better and come up with new tools to help biologists. The same is true for medicine. All these areas of science interact and help each other, and a lot of scientists and doctors now work in teams to answer questions together.
International School in MD

What happens if a human has over a thousand chromosomes
Dick Okita, Ph.D.: This is an interesting question. The human body does have over a thousand chromosomes when one considers all of the cells that make up the body. But an individual human cell only contains 23 chromosomes and if there are more than this number, the body may not function normally. For example, a disorder called Down syndrome occurs when there is an extra copy of chromosome 21.
Montgomery Middle School in CA (7th grade student)

How do toxins pass through the plasma membrane?
Lee Slice, Ph.D.: That is a very good question. There are several ways that toxins can enter cells. Some toxins are proteins that are produced by microorganisms such as bacteria. Some of these toxins are multi-component proteins that can create a channel in the cell's membrane and inject the toxin protein into the cell. Other toxins can bind to cell surface receptors and hitch a ride into the cell with the receptor. Other toxins are small molecules that can pass into the cell membrane because they dissolve in the lipid layer of the membrane. One toxin that does this is dioxin. I hope this helps, you can find more information at http://www.niehs.nih.gov.
Sidwell Friends High School in DC (9th grade student)

What genetic disorders come from mutations in the DNA that codes for centrioles?
Joe Gindhart, Ph.D.: There has been some controversy over the years regarding whether centrioles contain DNA. While some DNA stains label centrioles, DNA has not been observed directly by microscopy. More interesting to me is the observation that some cells couple DNA replication to centriole duplication, other cell types do not. Furthermore, some organisms such as plants lack centrioles entirely, but they can make mitotic spindles and undergo cell division. Trends in Cell Biology, volume 18, pages 389-396 (2008) is a nice review of our current understanding of centriole duplication.
Sidwell Friends High School in DC (9th grade student)

Why is apoptosis important?
Stefan Maas, Ph.D.: Apoptosis, often also called 'programmed cell death' is a mechanism for organisms to eliminate individual cells. This mostly happens during normal development of a fertilized egg to the embryo and further to the adult organism. It exemplifies how some cells are sacrificed for the good of the whole organism because they are not needed at the later stages of development. For example, during human embryonic development the formation of our fingers and toes involves the apoptotic elimination of cells that initially fill the space between them. At other times, a cell may undergo apoptosis because it has been damaged beyond repair and, again for the good of the organism, it kills itself so that the organism can continue to thrive.
Lexington High School in SC (12th grade student)

Does the radiation from microwaves affect women's eggs?
Kirstie Saltsman, Ph.D.: Great question! Microwaves heat things up by causing water molecules to vibrate. Your body contains water so if you were exposed to microwaves your tissues could feel the heat! But microwave ovens are designed to keep the microwaves inside the oven, so they don't cause harm to a woman's eggs or to any part of the body. The only cause for concern would be if the oven door were damaged and microwaves leaked out.
Sidwell Friends High School in DC (9th grade student)

What would happen if all of your nerve cells died?
Joe Gindhart, Ph.D.: Sadly, you would be dead, too. Nerve cells are required for bodily functions such as breathing, blood circulation, and digestion.
Piney Grove Middle School in GA (7th grade student)

Can you explain how the selection of brain neurons gives rise consc​iousness?
Lee Slice, Ph.D.: Is this Skynet question for the movie Terminator? But seriously this is a very difficult question to answer because essentially no one knows. In people, billions of neurons in the brain are interconnected using synapses so that they can transmit information to the neighboring neurons. This communication in the vastly large scale results in higher thinking and consciousness. Another way to look at it is illustrated in the movie 2001: A Space Odyssey where the HAL 9000 computer, which was very smart was made to loose this ability by sequentially removing CPU and memory units. HAL ended up singing a song.
Damascus High Scool in MD (12th grade student)

Are cells specific colors or can they be any color?
Peggy Weidman, Ph.D.: Good question! In nature, most cells are transparent and without color. Animal cells that have a lot of iron, like red blood cells, are deep red. Cells that contain the substance melanin are often brown. It is the absence of melanin that makes eyes blue. Scientists have tricks for making different parts of cells glow with fluorescent dyes. These are beautiful but artificial.
Zion Lutheran School in TX (6th grade student)

What is the magnification needed to view ribosomes in a cell?
Alexandra Ainsztein, Ph.D.: Ribosomes can be viewed using light microscopy. The ribosome is a large and complex molecular machine, found within all living cells and are about 20-30nm depending upon the cell type.
Zion Lutheran School in TX (6th grade student)

Which living organism has the most cells?
John Laffan, Ph.D.: There are many contenders for this prize. My favorite is a clonal organism, a grove of Aspen in Utah. It is projected to weigh about 6 million kg made up of zillions of cells. There is also a fungus in eastern Oregon which covers almost 9 square kilometers. We actually have not counted the number of cells in these giant organisms so there is some debate.
Queen of the Rosary in IL (7th grade teacher)

What are some of the chemicals that cell membranes are made of?
Jean Chin, Ph.D.: Cell membranes are made up of proteins, lipids or fats, and carbohydrates or sugars. There are many membrane lipids called phospholipids and cholesterol and some of these are on the outer side of the membrane while other lipids stay in the inner side or cytosolic membrane. Sugars are usually on the outer side of the membrane on proteins.
Zion Lutheran School in TX (6th grade student)

How many different types of cells are found within the body?
Peggy Weidman, Ph.D.: Your body contains trillions of cells, organized into more than 200 major types.
Piney Grove Middle School in GA (7th grade student)

Do you research environmentally friendly products as well at your facility?
Joe Gindhart, Ph.D.: The NIH supports research that explores our relationship with the environment and the chemicals in it. Our NIH Institute (NIGMS) supports research in green chemistry and pharmacology by providing research funding to scientists interested in this topic.
McKeesport High School in PA (10th grade student)

Why can't we replace nerve cells?
Stefan Maas, Ph.D.: To date it is not possible to replace specific cells within the brain since each brain cell is highly specialized and highly connected to many other cells. Also, the brain is not easily accessible and usually, people develop clinical symptoms only once a large number of brain cells are lost or damaged (such as in Alzheimer's and Parkinson's Disease). However, there are human clinical trials where it is being attempted to supply the brain with 'fresh' cells in order to replace other cells that might have died. These experimental trials are at a very preliminary stage and it is not clear when or if at all such cellular treatments will be successful.
Piney Grove Middle School in GA (7th grade student)

How do scientists study cells when they are so small?
Ward Smith, Ph.D.: Cells are not really that small for modern research. We actually have instruments to study individual molecules and atoms. Typically, cells range in size from 10 - 300 microns (1 micron is one millionth of a meter). Molecules, which are also studied in biology, are a few billionths of a meter in size. Cells are studied with light microscopes and other instruments, particularly in combination with molecules that cause cells to light up.
Piney Grove Middle School in GA (7th grade student)

Approximately how many cells would fit on the eraser of a pencil?
Alexandra Ainsztein, Ph.D.: This is an interesting question. It depends on how big the eraser is and how big the cells are as both can vary. The average size of the eraser is 4mm cubed and the average cell is 50 microns in length....so the answer is A LOT!
Piney Grove Middle School in GA (7th grade student)

Are there more good types of bacteria or bad types?
Lee Slice, Ph.D.: There are certainly good types and bad types of bacteria. People have evolved for several thousand years in the constant presence of bacteria. The human gastrointestinal tract contains billions of bacteria and mostly of a few types that actually help maintain human health. But when you eat a pathogenic bacteria like Vibrio cholerae, which causes Cholera, then a serious disease can result. Also most stomach ulcers are caused by a bacterial infection (H. pylori).
Piney Grove Middle School in GA (7th grade student)

What are the names and functions of some of your tools working with cells?
Jean Chin, Ph.D.: Depending on what you want to know about cells, there are tools to watch as cells divide or move towards something good to eat or away from something bad or poisonous. Scientists have found that microscopes can be used to follow specific proteins tagged with fluorescent proteins of different colors. Other scientists like to look at just the nucleus or mitochondria and have cell fractionation methods to break open cells to study them. They have also developed lots of biochemical assays or tests to follow reactions. Maybe you will help to develop new tools to study the cell someday!
McKeesport High School in PA (10th grade student)

How do blood cells differentiate?
Joe Gindhart, Ph.D.: Blood stem cells differentiate into many different cell types. These cells are pluripotent, meaning that they can divide and differentiate into several different types of cells, but not all cell types. Blood stem cells receive signals from the extracellular environment that provide instructive cues regarding what blood cell type to become after cell division is completed.
Mapletown Jr./Sr. High School in PA (student)

Which organelles are referred to as semiautonomous?
Alexandra Ainsztein, Ph.D.: Mitochondria and chloroplasts are semiautonomous because they have their own DNA. These organelles can also self replicate (divide) by fission.
Dedham High School in MA (11th grade student)

How did scientists discover cells?
Ward Smith, Ph.D.: The existence of cells was first confirmed by Robert Hooke, a British natural philosopher of the mid 1600s. Hooke was using the newly invented microscope to examine matter.
Piney Grove Middle School in GA (7th grade student)

How do cells work in the body and affect our daily life?
Peggy Weidman, Ph.D.: This is a tricky one! The cells in organs of your body have essential and specific functions but are in communication with cells all over your body. It is the network between all the cells that keeps you going. If this network is disrupted (such as some cells not working right), you get a disease. For more information what specific types of cells do, check the book "Inside the Cell" on our website.
McKeesport High School in PA (10th grade student)

How many cells are there on Earth?
Ward Smith, Ph.D.: There is no way to calculate the number of cells on earth. Cells exist in many sizes and in many densities. There certainly are a large number of cells on earth but the actual number is not known.
Piney Grove Middle School in GA (7th grade student)

How soon are you in the discovery of detecting genetic diseases in prenatal development?
Stefan Maas, Ph.D.: The most advanced methods that are being developed currently for prenatal diagnosis of genetic disease only require a blood sample from the pregnant mother. Because during the development of the fetus cells are regularly shed from the fetus, genetic material (DNA) also gets into the blood of the mother. Technology has recently advanced such that it has become possible to find and isolate the DNA from the fetus and analyze its composition along with that of the mother. Doing this allows to look for the genetic makeup of the fetus and look for known types of changes in the DNA that cause a genetic disease. This new technology is likely in the future to replace more invasive methods that are currently used for prenatal testing, such as amniocentesis and chorionic villus sampling.
McKeesport High School in PA (10th grade student)

Are there ways to prevent certain genetic diseases?
Lee Slice, Ph.D.: Genetic diseases are a result of gene mutations in our DNA. In order to cure this, we would have to fix the genetic mutation by directly changing the DNA or developing a drug that would remedy the defective protein that results from the mutated DNA. An example for this is sickle cell anemia, which is caused by a single DNA base pair mutation in the gene for hemoglobin. The results in a sticky spot on hemoglobin that allows the mutated hemoglobin to stick together like beads on a string. If a small drug can be found to cover this sticky patch then this would stop the hemoglobin from sticking together.
McKeesport High School in PA (10th grade student)

what is a cell membrane?
Jean Chin, Ph.D.: The cell membrane is what keeps cell components inside the cell and prevents leakage or bursting. It is mainly composed of proteins and lipids so it is oily. The membrane helps to keep some things out and other things in. The cell membrane has proteins called transporters, channels and receptors which take up nutrients, drugs, metals and respond to signals from the cell environment.
Heritage High School in WA (10th grade student)

Evolution is a known fact. Why are some schools in the U.S. against teaching it?
Joe Gindhart, Ph.D.: The instructional curriculum of science courses is decided by local and state boards of education. Biology research provides evidence supporting evolution as a mechanism for generating diverse life forms. NIGMS researchers use model organisms such as fruit flies, yeast, and plants to study cellular processes that share components and mechanisms with higher organisms.
Grover School in TN (9th grade student)

Is it possible for brain cells to replicate?
Lee Slice, Ph.D.: Yes, even though neurons do not generally divide there are stem cells in the brain that do divide and the daughter cells do differentiate into neural cells in the brain.
Dedham High School in MA (11th grade student)

Is the lysosome membrane bound?
Alexandra Ainsztein, Ph.D.: yes
Dedham High School in MA (11th grade student)

How do viruses attack your cells?
Jean Chin, Ph.D.: Some viruses attack cells by hijacking normal cell membrane structures and processes. Some may bind to membrane patches which are rich in membrane fats called cholesterol and sphingolipids. They are then taken up by endocytosis into the cell. The membrane surrounds the virus and engulfs it.
Piney Grove Middle School in GA (7th grade student)

How do prokaryotic and eukaryotic cells differ?
Ward Smith, Ph.D.: Eukaryotic cells contain a nucleus and other organelles and often have specialized functions. Prokaryotic cells are less complex, without a nucleus and commonly exist as single cells. Prokaryotic cells are generally smaller (1 - 10 microns) than eukaryotic cells (10 -100 microns).
Dedham High School in MA (11th grade student)

Are microtubules located in both animal and plant cells?
Alexandra Ainsztein, Ph.D.: Yes. Microtubules are evolutionary conserved structures that form the skeletal support of the cell. They are involved in cell division, and cell motility as well.
Dedham High School in MA (11th grade student)

How close are you to regenerating organs in tissue engineering research???
Lee Slice, Ph.D.: I just got back from a stem cell meeting that presented a talk about transplanting engineered retinas from stem cells. The would help restore sight to patients with macular degeneration. They stated that they were about to get approval for human trial and they speculated that within 5 years, this would be a viable treatment.
McKeesport High School in PA (10th grade student)

What causes cells to develop abnormally and develop into cancer?
Stefan Maas, Ph.D.: That is a good question and does not have a simple or single answer. Generally, in order for a cell to become a cancerous cell it needs to acquire properties, such as the ability to keep growing despite the environment telling it to stop. On the molecular level this often means that a certain genetic change (mutation) makes the pre-cancerous cell ignore adjacent cell's signals that they are already touching and therefore should stop dividing further. This initial genetic change then often makes the cell likely to acquire additional mutations and it will gain further properties, for example, the ability to migrate and form metastases. So the initial cause for all of this is often some form of stress or damage to the cell resulting in the initial genetic change. From there on, most of these damaged cells will be removed by immune cells or they just die by themselves (see the answer to a previous question on apoptosis) but some can survive and go on to the next level of becoming cancerous.
McKeesport High School in PA (10th grade student)

Why do lysosomes digest extra cell material?
Joe Gindhart, Ph.D.: Lysosomes are, in some ways, the "trash can" of the cell. They digest both extracellular and intracellular material, such as damaged mitochondria. Vesicles bud from the plasma membrane and can fuse with the endosome. Endosome contents are sorted to a variety of cell compartments, including the lysosome. For example, the lysosome is used to digest extracellular signals and transmembrane receptors to attenuate a cell's response to that signal.
Dedham High School in MA (11th grade student)

Why do cancer cells form?
Stefan Maas, Ph.D.: Great question: please see the answer to question 106, which was very similar.
Dedham High School in MA (11th grade student)

What inspired you take an interest in biology and its beautiful diversity?
Ward Smith, Ph.D.: I was interested in science form an early age. I love the challenge of tackling a complex and important question. The excitement when you participate in a breakthrough finding is tremendous. I firmly believe that to have a successful career you need to follow a path that really captures your interest.
Dedham High School in MA (11th grade student)

What is a nuclear pore?
Alexandra Ainsztein, Ph.D.: This is a structure inserted the nuclear membrane through which molecules are transported from the nucleus to the cytoplasm. The nuclear pore complex is a multisubunit (multi-protein) and one of much investigation.
Dedham High School in MA (11th grade student)

Is there a size difference between plant and animal cells?
Joe Gindhart, Ph.D.: Yes, but there can be overlap between the size of plant and animal cells. Both plant and animal cells vary widely in size, based upon their function. A chicken egg is much bigger, a neuron is much longer, and a red blood cell is smaller than a typical plant cell.
Piney Grove Middle School in GA (7th grade teacher)

Is the Golgi complex membrane bound? Also, are they found in prokaryotes and eukaryotes?
Jean Chin, Ph.D.: Yes, the Golgi complex is membrane bound and its membrane composition is slightly different from the membranes of the cell membrane, the mitochondria, the endoplasmic reticulum, the nucleus and other organelles. So far as we know, prokaryotes only have cell membranes and do not have the intracellular organelles found in eukaryotes.
Dedham High School in MA (11th grade student)

How do stem cells used in treatment of disorders like Parkinsons or spinal cord injury know how to target that particular area.
Lee Slice, Ph.D.: That is an interesting question, the two properties that define stem cells is the ability to replicate itself and the ability to become any cell in the body. The trick is to get stem cells into the area of the brain or spinal cord where they are needed to replenish lost cells. Once they are there, the stem cells communicate with other cells that are present. The stem cells divide and then differentiate into specific cells by a highly regulated process.
Lexington High School in SC (12th grade student)

How much smaller is the nucleus than the actual cell?
Alexandra Ainsztein, Ph.D.: Depending on the cell type this may vary, but on average the nucleus is a about half the size.
Piney Grove Middle School in GA (7th grade student)

Which of the following are membrane bound: Vacuoles Mitochondrion Chloroplasts Peroxisome Cell wall Cell membrane Microvilli Flagellum Microtubules Cytoskeleton
Joe Gindhart, Ph.D.: Is this a quiz? :-) Vacuoles Mitochondrion Chloroplasts Peroxisome Cell membrane
Dedham High School in MA (11th grade student)

Why do we exist?
Ward Smith, Ph.D.: Very good question. But not one I can answer. We are trying to answer questions related to the biology of the cell in this forum.
Dedham High School in MA (11th grade student)

Whats your favorite part about biology? Explain in a three paragraph essay stating why.
Alexandra Ainsztein, Ph.D.: While I could go on and on, I'll be brief. My favorite part of biology is understanding how all these small machines work together to create an organism. Biology is a complex and intricate dance of components. I became a cell biologist when I looked down the microscope in the 6th grade!
Dedham High School in MA (11th grade student)

What hormones are used to creates "love"?
Ward Smith, Ph.D.: To me, love involves both a physiological response and an emotional one. The physiological response involves many molecules such as neurotransmitters, chemicals and hormone molecules such as serotonin and oxytocin.
Dedham High School in MA (11th grade student)

Would we be able to survive with only one nerve cell?
Joe Gindhart, Ph.D.: There are organisms, such as jellyfish and nematodes, that can survive with very few neurons, but our nervous system is composed of billions of neurons. Removing all except one would certainly be bad for you!
Piney Grove Middle School in GA (7th grade teacher)

Are there any genes that are superior to others? And if so why?
Stefan Maas, Ph.D.: Some genes are essential for the survival of the organism, so if the function of one of these is lost, the organism cannot live. The loss of non-essential genes might lead to a disease or other observable 'phenotype', but the organism will still live. In that respect, the essential genes are superior in terms of immediate importance. Among the essential genes are for example those that work during the early development of the embryo and others whose function is fundamental to the workings of every cell. An interesting line of research is trying to figure out what the essential set of genes is that an organism needs to live. One approach (top-down) is to take a very simple, single cell organism and delete individual genes and looking for what the minimal number is. The other approach (bottom-up) is to build a synthetic cell out of individual genes and see how many functions are needed to make the cell able to live independently. The answer to this question is still out..
Dedham High School in MA (11th grade student)

Can someone please explain the significance of compartmentalization for eukaryotic cells.
Peggy Weidman, Ph.D.: It greatly increases efficiency when all the proteins involved in a specific function are collected together in one place. Also, many of the most important functions of the cell occur at and in membranes. By having a large number of membrane organelles inside the cell, the cell can maintain enough membrane to function properly.
Dedham High School in MA (11th grade student)

How do you explain the significance of compartmentalization for eukaryotic cells?
Jean Chin, Ph.D.: Some biological processes need to be isolated or separated from other reactions so compartmentalization is very significant and necessary. Some reactions require starting material available only in specific intracellular locations. DNA transcription, for example, takes place in the nucleus where DNA is located while translation or protein synthesis takes place in the ribosomes where all the required proteins and nucleic acids are.
Dedham High School in MA (11th grade student)

What is the significance of compartmentalization for eukaryotic cells.
Peggy Weidman, Ph.D.: See answer to question 121
Dedham High School in MA (10th grade student)

What are microvilli? Are they found in plant or animal cells? Are they membrane bound?
Joe Gindhart, Ph.D.: Microvilli are finger-like structures found on the apical (top) surface of some types of animal cells. They are projections of the plasma membrane, so they are open to the cytoplasm; by analogy, the inside of our fingers are open to our hand. They increase the surface area of the plasma membrane.
Dedham High School in MA (11th grade student)

Would we ever be able to inject humans with chlorophyl so we could make our own energy laying in the sun?
Alexandra Ainsztein, Ph.D.: This is an interesting question! While it is uncertain whether this could occur in humans, there are tiny aphids (pea aphids) that act like plants and trap light to convert to energy.
Piney Grove Middle School in GA (7th grade teacher)

If an organism dies, do all of it's cells immediate​ly die too?
Jean Chin, Ph.D.: No, some cells such as those in hair cells live on for a while after a person dies. Other cells that continue include finger nail cells.
Piney Grove Middle School in GA (7th grade student)

My friend clark and i are wondering why cells are so small......sincerely devin
Ward Smith, Ph.D.: Cells have the size that is needed to accomplish the job they do - degrade unwanted material in the cell, communicate with other cells and other functions. Actually, small is a relative term. From the perspective of the electron for examples, cells are HUGE.
Dedham High School in MA (11th grade student)

What are the 3 stages of cell signaling?
Stefan Maas, Ph.D.: One traditional way to look at this is to consider the reception of the signal as the first stage (like a hormone binding to its receptor in the cell membrane), the the transduction of that signal from the membrane into and through the cell (where the receptor signal is transmitted through intermediate signaling molecules) as the second stage, and then the response of the cell to the signal (such as stopping or starting to grow) as the third stage. One could consider other ways to describe levels or stages of cell signaling, since the communication between cells involves events that occur outside of the cells (like the recognition of one cell by another through molecules on their outside), then many levels of signaling that lie within the cells and their cellular compartments, and then within an organism, the cells within and between different tissues communicate with each other. Finally, some cells can move physically through the body and mediate another type (or stage) of cell signaling.
Dedham High School in MA (11th grade student)

Why are cells called cells? How did they get the name?
Michelle Hamlet, Ph.D.: Hi, Dedham High, The term cells came from British scientist Robert Hooke, who came up with the name when he saw these cool compartments looking at a piece of cork under a microscope.
Dedham High School in MA (11th grade student)

what is cell communication? why is it important to cells?
Lee Slice, Ph.D.: Cell communication involves exchanging information between two distinct cells or relaying information from one side of a membrane to the other. Alot of this communication involves cell signaling using receptors and small molecules that interact with receptors. This cellular communication is required for organ development, assembly and function. Intracellular signaling is important for the cell to maintain itself and to function properly.
Dedham High School in MA (10th grade student)

How do steroid hormones cause cellular responses?
Lee Slice, Ph.D.: Good question, steroids bind to nuclear receptors that then bind to DNA. This causes changes in the expression of the targeted genes. The resulting proteins than act on their targets in the cell.
Dedham High School in MA (11th grade student)

How does the body get rid of dead cells?
Jean Chin, Ph.D.: Dead cells are removed from the body in different ways. Skin cells sloughed off or rubbed off while dead hair falls out. Some cells in the blood called macrophages eat up dead cells as well as bacteria.
Piney Grove Middle School in GA (7th grade student)

Approximately how long do hair cells and finger nail cells live after a person dies?
Michelle Hamlet, Ph.D.: One theory is that the body's dehydration after death gives the appearance that hair and finger nail cells continue to grow after death. The British Medical Journal has information about this.
Piney Grove Middle School in GA (7th grade student)

Do any cells have natural color?
Joe Gindhart, Ph.D.: Yes! Blueberries are blue, carrots are orange, plants are green, mustard is yellow, the cells of our retina are black, eggplants are purple, all because of pigments that are present in those cells. Many of the pigments used to dye clothing are isolated from plant and animal sources; while some pigments are man-made, many are still derived from natural products.
Piney Grove Middle School in GA (7th grade student)

What color is a nucleus?
Peggy Weidman, Ph.D.: In a living cell, the nucleus is almost completely transparent and colorless. You can't really see it unless you know what to look for! When scientists take photographs of cells in the microscope, they usually treat the cells first with a dye that makes the nucleus blue or purplish blue. Because of this, the nucleus in most drawings of cells are also blue.
Piney Grove Middle School in GA (7th grade student)

What causes cells to die?
Jean Chin, Ph.D.: All cells die eventually but some cells die prematurely for different reasons. Some die because they have been injured or poisoned. Others die because they are sacrificing themselves to stop invading bacteria or viruses from infecting neighboring cells. Still other cells are involved in tissue remodeling such as cutting away the excess tissue for the formation of fingers and toes. One of the signals for cell death is the flipping of a membrane lipid called phosphatidylserine or PS from the inner cell membrane to the outer membrane.
Piney Grove Middle School in GA (7th grade student)

How do cells end up forming tumors?
Lee Slice, Ph.D.: Tumors are a collection of cancer cells that continue to divide at a significantly higher rate compared to normal cells. An example would be colorectal cancer that can form tumors in the large intestines. It starts with a mutation in colon stem cells that allow the daughter cells to continue to divide instead of stopping and dying in about a week. This results in a polyp that if detected can be cured by removing it. That is why it is recommended that every 50 year old should have a colonoscopy. It takes about 5 years to develop a colorectal tumor.
Piney Grove Middle School in GA (7th grade student)

Moderator: Our final set of experts includes Dr. Chin, Dr. Hamlet, Dr. Slice, Dr. Weidman, Dr. Reddy, Dr. Smith, and Dr. Gindhart. Their bios are here.​

Is the cell cycle controlled by time of day?
Michelle Hamlet, Ph.D.: What a great question! As recently as 2003, there was a study to ask this very question. It turns out that there is in fact a connection between the genes that control the cell cycle and genes that control our circadian clock (which controls our the body's 24 hour clock). In the study, the scientists showed that if a clock gene is broken, the cell cycle gene did not turn on properly. Pretty cool, huh? Check out the paper for yourself: Matsuo et al., 302 (5643): 255-259.
Blessed Sacrament School in NJ (8th grade student)

What do we know about the instructions in DNA that turn genes on and off?
Mike Reddy, Ph.D.: Well, we know a LOT! And in fact, it is largely THIS exact question that drove much of the development of what is known as "Molecular Biology" over the past 60 years and counting. Early on - in trying to figure out the answer to this question - scientists realized that specific PROTEINS bound to very, very specific locations on the DNA. These locations are generally referred to as PROMOTERS and they are a short string of a special DNA sequence. Sometimes the binding of these proteins to these promoter sequences turn the gene ON. But sometimes, their binding turns the genes OFF. These proteins turn genes on or off generally by interacting with another enzyme called RNA polymerase. Now in recent times (the past 10 years and less) scientists have discovered that in many case it is the binding of small pieces of RNA (and not proteins) that cause many genes to turn on or off. Scientists are discovering that there are many, many of these small regulatory RNAs in cells. Ho w these small RNA pieces find their exact place to bind on a DNA molecule is one of the most exciting areas in modern biology!!
Blessed Sacrament School in NJ (8th grade student)

Can we use X-rays to see proteins?
Ward Smith, Ph.D.: Yes, use of X-rays is one of the methods to determine the structure of proteins. In structure determination, X-rays diffract from crystalline samples of a protein and the resulting 3-dimentional diffraction pattern can be used to locate the electrons (therefore the atoms ) in a protein molecule. The wavelength of X-rays used to determine protein structures in this way is much smaller than the wavelength used for dental or medical X-rays.
Blessed Sacrament School in NJ (8th grade student)

Do bacteria have the instructions in their genes to eat any kind of sugar?
Jean Chin, Ph.D.: This is an interesting question! All kinds of sugars are digested by bacteria but they may not have every enzyme to eat any kind of sugar. However, bacteria are able to adapt their genes or instructions over time to digesting unusual and new sugars and other things such as rubber tires and oil. In fact, bacteria have been recruited to learn how to eat up all kinds of things we don't want around in the environment.
Blessed Sacrament School in NJ (8th grade student)

Can we have too much iron in our bodies?
Peggy Weidman, Ph.D.: We have a system that senses how much iron we have in our bodies and prevents us from collecting too much. We store a little bit of iron in our livers so that we have enough to make hemoglobin for red blood cells and the like. There is a very common disease called hemochromatosis where the regulation of iron uptake is haywire and people take up way too much iron. This iron accumulates in the liver to such a great extent that the liver can't work right. The only good thing about this disease is that the iron can be kept from accumulating in the liver by removing blood from the patient on a regular basis. The making of replacement blood cells uses up the excess iron.
Blessed Sacrament School in NJ (8th grade student)

How can "G-proteins" do so many different things in our bodies?
Lee Slice, Ph.D.: There are several types of G-proteins, heterotrimeric G-proteins and small G-proteins called GTPases. G-proteins bind guanosine triphosphate or GTP and that activates other signaling proteins that are associated with the G-protein. After a little while, the G-protein changes the GTP to GDP, which turns off the G-protein. So G-proteins are little timers for signaling. Heterotrimeric G-proteins are coupled to seven transmembrane receptors. There are over a thousand different seven transmembrane receptors so there are a lot of different possibilities for activation of G-proteins in multiple cell types by light, hormones, odorants and other molecules that can bind to seven transmembrane receptors. This is a great question.
Our Lady of Victories in NJ (7th grade student)

Can RNA be used to make protein and DNA?
Jean Chin, Ph.D.: Usually DNA is used to make RNA and then protein but, while many viruses contain DNA, some viruses called retroviruses use RNA instead of DNA to reproduce. The single-stranded RNA in retrovirus is used to make the double-stranded DNA or the template for synthesizing messenger RNA and then protein. So, if you are a retrovirus, you would use RNA!
Our Lady of Victories in NJ (7th grade student)

Is there any studies or research being done for cell research regarding stem cell therapy?
Michelle Hamlet, Ph.D.: Bone marrow transplantation is the most common stem cell therapy today, but in Japan there will be human clinical trials for generating retinas from re-engineered fibroblasts.
N/A in FL

Why is it so hard to cure so many basic human ailments like the common cold or common heart burn?
Ward Smith, Ph.D.: Human biology is very complex. The only way to arrive at cures is to completely understand the underlying biology of disease. Our approach has resulted in tangible successes. Life spans are longer for each generation as a result of medical advances. Some diseases that were once feared or even considered a death sentence are now manageable - AIDS, TB, polio. We are making progress in a number of areas. Many cancers can be treated, and we know how to use gene analysis to recognize some inherited diseases.
David in FL

Moderator: Wow! What a way to "cell"ebrate! Thank you to everyone who sent in questions and to all our great experts who answered them! Everyone gets an A+!