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David Deamer is Chair of Biomolecular Engineering and professor of Chemistry and Biochemistry at the University of California, Santa Cruz. His research looks at the role of membranes in the origin of cellular life on Earth. He has investigated whether cell membrane-like structures were available on the early Earth and could have provided a home for more complex molecules like proteins and nucleic acids, leading to a system of molecules with the properties of life. |
David Deamer answered selected viewer questions about artificial life research and how it relates to Earth's earliest life-forms on October 21, 2005. Please note we are no longer accepting questions, but please see our links and books section for additional information on artificial life. Q: Hello, my name is Abby. I watched your NOVA program and was excited to hear that one day scientists might be able to make a real, living creature. If this happens, would it be possible to make a dragon? A: Hi Abigail, I love the idea of making a dragon! But flying, fire-breathing dragons are most likely mythical, rather than real animals, so I'm not sure how we would design a dragon. Another problem is that we still don't know for sure how to make a simple little bacterial cell. I'm afraid that making a dragon is far in the future. Q: My question has to do with irreducible complexity, and ultimately with the intelligent design vs. natural evolution debate. The problem is this: Coded in all DNA are the instructions to build the enzymes that allow the DNA to replicate itself; therefore it's difficult not to require the assumption that the first "proto-DNA" molecules assembled themselves with this self-replicating machinery already fully in place—otherwise how would the first DNA have propagated itself? How do biochemists and geneticists account for this apparent "chicken-or-egg first" quandary? And what evidence do they adduce to back up this accounting? Finally, might there exist natural environments on Earth where self-replicating molecules or extremely simple forms of life are spontaneously emerging now? A: Dear Rob, You bring up some interesting and important questions. They can't be answered yet, but we are making a little progress. Your initial point assumes that a DNA-RNA-protein world sprang into existence spontaneously, and this seems unlikely, as you noted. One way out of the conundrum is to consider that simpler forms of genetic information and catalysts were components of primitive cellular life. For instance, certain kinds of RNA are called ribozymes because they can act as catalysts. They can also carry genetic information in their base sequence, and this has led to the suggestion that an RNA world came first, in which RNA served both as a catalyst and as a genetic material. David Bartel and his co-workers have in fact discovered a ribozyme that can copy a sequence of 14 nucleotides. If we can ever find a ribozyme that is able to copy itself entirely, this would solve the chicken-egg problem. In regard to your second question about whether simple forms of life may still be appearing, probably not, because they would quickly be devoured by more advanced life that inhabits the Earth today. However, I think we can learn something by adding simple chemicals to geothermal environments and looking for both degradative and synthetic reactions. In my research supported by the NASA Astrobiology Institute, we are carrying out such experiments in Kamchatka, Iceland and most recently Mt. Lassen, California, as shown in the NOVA program. You also mentioned the intelligent design (ID) question. Just last week I participated in a forum with Paul Nelson and Robert D'Agostino, both proponents of ID. My main point against teaching ID as an alternative to evolution is that ID does not qualify as science. It is an opinion based on religious convictions, not on factual evidence, nor can it be tested in the usual way. Q: Supposing the experiment [to create artificial life] succeeds; to what extent will the fact that our intellect is responsible for the creation of life explain the origins of life on Earth? Everything considered, wouldn't this be like building a complex machine from its parts with an instruction manual, or is there more to it? A: Dear George, You are right on target. The first kinds of artificial life in the laboratory will use components like ribosomes that we don't yet know how to make from simpler materials. In other words, it will be an engineering approach using a tool kit and instruction manual provided by living organisms. But we are also looking for self-assembly processes that can lead to structures exhibiting certain properties of life. A simple example is the self-assembly of lipids into cell-sized membranous vesicles. We did not know this was possible until it was first demonstrated in the 1960s. We are now trying to find ways in which self-assembly processes can make polymers of life. For instance, Jim Ferris and his co-workers have shown that nucleotides can assemble on clay mineral surfaces in such a way that short polymers of RNA are produced. Q: I was going to begin a science fair project regarding this subject. It involves the artificial synthesis of life in a simulated early Earth environment and other planets. It would be modeled like the Miller-Urey Origin of Life experiment. If you have any suggestions about how to go about doing my project, it would be greatly appreciated. Thank you for taking the time to read this. A: Hi Andrew, This would be pretty complicated, because you will require a source of hydrogen gas, methane, and ammonia, as well as a high voltage electrical spark to drive the reaction. You would need to be very careful, since hydrogen and methane are explosive under certain conditions! I can suggest something simpler, but it depends on what equipment you have to work with. Do you have access to a microscope and digital camera? If so you might try making lipid vesicles from lecithin that you can buy at a health food store. For cellular life to begin, some sort of cell membrane is required, and there are quite a few experiments you can do with lecithin that are related to the origin of life. You can use the digital camera to take photos right through your microscope. If you would like to try this, please visit my Web page at the University of California, Santa Cruz, and send me an email. Q: What would you predict to be the earliest source of energy for the first life-forms; chemosynthetic (energy from inorganic molecules) or heterotrophic (energy from organic molecules)? A: Dear Dr. Backer, Good question, and I have given this some thought over the years. Chemosynthetic energy is available almost everywhere, and modern microbial life makes good use of it even in environments such as hydrothermal vents. However, using this energy requires a membrane that can maintain a chemiosmotic gradient of protons, so the first cells would need a source of lipid-like molecules as well as an electron transport process that can pump protons. Heterotrophic energy may have also been available if we assume that organic compounds were present on the early Earth. The question is how to capture the chemical energy and keep it in one place, so again a membrane compartment is needed. We should also consider light energy, which requires both a membrane and pigment molecules for it to be captured. I don't think we know enough to make an informed choice yet, so all three energy sources should be investigated. [Editor's note: Below are two related questions that Dr. Deamer answered in one response.] Q: Define 'life.' When we finally encounter 'it' elsewhere, how can we be sure 'it' is alive? A.C. Clarke wrote of a distant planet with living crystals that took a thousand years to form a thought. Is that crystal alive? And how will we know if 'it' is 'real', or Memorex, i.e., artificial? Q: 1.How does one distinguish between life and non-life? 2.What are the basic requisites for life? A: Hi Rick and David, You are asking a question that many scientists are also thinking about. There doesn't seem to be an easy answer that satisfies everyone. Life is a very complex phenomenon, so a definition must reflect the complexity. I tried to do this for the first cellular life, and I came up with the following, which is more a description than a definition:
[Editor's Note: The question of what defines life is also addressed, in a light-hearted way, elsewhere on this Web site in Let's Make a Microbe!] Q: Does research such as this affect the development of technology not related to creating synthetic life? I am thinking, for instance, of how mimicking the biological mechanisms in the rods and cones of an organic eye could help develop better cameras or whatnot. A: Dear Jon, Yes, basic research often leads to unexpected discoveries that have practical applications, as you mentioned above. A good example is the discovery of semiconductors by someone doing basic research in physics. Who would have guessed that this would lead to transistors, then computer chips and a trillion dollar industry? In my lab, we found that a protein called hemolysin could transport DNA across lipid bilayer membranes, and that we could detect each DNA molecule by a change of ionic current. We are now trying to make an artificial version of hemolysin that can sequence DNA at thousands of bases per second. Q: Are there any other 'duplicating' molecules on Earth that are not RNA or DNA? Are there other known 'duplicating' molecules from the primitive Earth? A: RNA and DNA are the only compounds we know of that have complementary base pairing which allows them to replicate. Q: It was said in the program that the time when life will be derived in a lab is over the horizon or just around the corner. Just how long will it be, really, till we actually see this artificially derived life? A: Hi Jason, The answer depends on how we define artificial life. If we take apart a bacterial cell and put it back together into a simplified organism, that might happen in the next ten years. But if you want us to start from scratch, using as starting material chemicals like amino acids, nucleotides, phosphate, sugars, lipids and so on, that's a long way off. The only thing that makes me think it's not an impossible task is that life seems to have started this way nearly 4 billion years ago on the early Earth. If we can better understand how this happened, it might turn out to be easier than we think for a very simple form of life to begin. Q: What are the materials you need to make DNA? A: Hi Kaitlin, Wow! What a great question from a five-year-old! You need phosphate, a kind of sugar called deoxyribose, and four chemicals called bases that have the letters A, T, G, and C. If you link these together like beads on a string, you get DNA. Q: I like the idea of using science to try and explain life on Earth, but do you ever think that all the research might go too far one day? I'm concerned that in the future scientists might learn too much about how to create life and upset the natural processes that occur. Do you ever think that nature should just take its course while we just study it, but not try and alter it or try and become as powerful as nature? A: Dear Julie, You have asked a very thoughtful question that falls into a new field called bioethics. Let me say first that I don't think artificial life is much of a threat, even though science fiction writers love to scare us this way. The reason is that we can already engineer existing forms of viruses and bacteria so that they are very dangerous, so why bother making artificial life? The other part of your question is whether we should let nature take its course, study it but not try to control it. I personally hope that the human race will learn to live on the Earth without damaging the environment any more than we have already. On the other hand, if we let nature take its course, we would still have smallpox and polio viruses killing people. So it seems to me that we do need to control certain aspects of nature, but we should also accept that we are part of nature, and that we must learn to take care of our natural world. Q: When they were trying to get artificial life started by adding chemicals to conditions thought to exist on the early Earth, did they think about the possibility of adding a lightning strike? This charge could add something that could be missing due to the possible chemical changes and the energy created by the lightning. Just a thought. A: Hi Patrick, That's a very good thought! In fact, when Stanley Miller did his famous experiment in 1953, he found that amino acids could be synthesized by sparking a gas mixture with artificial lightning. So you are on the right track. Q: First I want to say that I love UCSC, and I am applying to be a freshman there next year as a bio major. I was just wondering if there is a specific organism that the synthetic life is going to be modeled after? Are researchers using pieces of another organism's genetic material to code for essential proteins? A: Hi Shane, I think you will enjoy being a student at UCSC—please come by to say hello when you arrive next year. To answer your questions, my guess is that we will use bacteria as a model for simple cells. The first step will be to break apart bacterial cells and then try to put the pieces back together. One such experiment was recently performed by Vincent Noireaux and Albert Libchaber at Rockefeller University, and their paper was published last year in PNAS [Proceedings of the National Academy of Sciences]. They broke up E. coli bacterial cells, then captured ribosomes and other molecular components in artificial lipid vesicles along with messenger RNA required for the synthesis of two specific proteins. Their synthetic cells "lived" for up to four days by taking up nutrients from the growth medium and producing substantial quantities of green fluorescent protein and hemolysin. The synthetic cells were not truly alive, however, since they could not grow or reproduce. Q: Will it eventually be possible to create completely original life from scratch for specific purposes? How about a carpet cleaning mouse or a huge, beef-shedding creature? A: Hi Jesse, This possibility is a long, long way into the future, if ever. But we can do a few things that are much simpler. For instance, artificial genes have been inserted into bacteria with the result that they produced valuable proteins like insulin and growth hormone. And the gene for a fluorescent protein has been inserted into goldfish to produce "GloFish" that you can buy over the Internet. |
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