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Biology: Heterotroph Hypothesis: Genetic Material


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About this Lesson

  • Type: Video Tutorial
  • Length: 11:53
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 128 MB
  • Posted: 07/01/2009

This lesson is part of the following series:

Biology Course (390 lessons, $198.00)
Biology: Evolution (37 lessons, $54.45)
Biology: The Origin of Life (6 lessons, $9.90)

Taught by Professor George Wolfe, this lesson was selected from a broader, comprehensive course, Biology. This course and others are available from Thinkwell, Inc. The full course can be found at The full course covers evolution, ecology, inorganic and organic chemistry, cell biology, respiration, molecular genetics, photosynthesis, biotechnology, cell reproduction, Mendelian genetics and mutation, population genetics and mutation, animal systems and homeostasis, evolution of life on earth, and plant systems and homeostasis.

George Wolfe brings 30+ years of teaching and curriculum writing experience to Thinkwell Biology. His teaching career started in Zaire, Africa where he taught Biology, Chemistry, Political Economics, and Physical Education in the Peace Corps. Since then, he's taught in the Western NY region, spending the last 20 years in the Rochester City School District where he is the Director of the Loudoun Academy of Science. Besides his teaching career, Mr. Wolfe has also been an Emmy-winning television host, fielding live questions for the PBS/WXXI production of Homework Hotline as well as writing and performing in "Football Physics" segments for the Buffalo Bills and the Discover Channel. His contributions to education have been extensive, serving on multiple advisory boards including the Cornell Institute of Physics Teachers, the Cornell Institute of Biology Teachers and the Harvard-Smithsonian Center for Astrophysics SportSmarts curriculum project. He has authored several publications including "The Nasonia Project", a lab series built around the genetics and behaviors of a parasitic wasp. He has received numerous awards throughout his teaching career including the NSTA Presidential Excellence Award, The National Association of Biology Teachers Outstanding Biology Teacher Award for New York State, The Shell Award for Outstanding Science Educator, and was recently inducted in the National Teaching Hall of Fame.

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As we continue our journey through the hot thin soup just like Charles Darwin, maybe just a few years earlier, we want to continue to talk about how the building blocks of life were formed. How did we get, how did this planet come up with these new molecules? A better way to put it, how did these new molecules get formed on this planet? Remember the first three steps. Step one, we needed to synthesis. Step two, not only did we need to synthesis we need to polymerize. We needed to bring these things together and make large, what we call, macro, big molecules, macromolecules. Three, we needed to come up with a test tube, a cell, an aggregation of these things so that we could actually start some chemistry happening within an enclosed shell. And four, the one that has eluded us for the longest amount of time, how and when did these protobionts become true bionts? When did they start to reproduce? Reproduction or heredity?
Now we're going to talk about this one, reproduction. I'll tell you, this is a tough nut to crack. Why? Well, let's talk about cellular reproduction. Let's get off organisms for a minute. Let's talk about cellular reproduction. In fact, let's talk about basic biochemistry of a cell in kind of a condensed version. First of all, what is the hereditary material of the cell? What, as you and I look around, what are we going to suspect is going to be the key to heredity? Well, everybody knows its DNA, deoxyribonucleic acid. One would suspect that in order for cells to reproduce properly they have to have DNA, but there's a dilemma with that. The dilemma is this. DNA, as we have found out, is an unbelievably complex material with an unbelievably complex mechanism of action. For DNA to spontaneously happen would be a very difficult thing for anyone to postulate. It's hard to imagine.
Let's go over a little bit about how DNA works. Remember the central dogma of Biology says the following. That DNA makes an intermediate, a much simpler form of nucleotide called RNA. RNA has a job. RNA actually grabs amino acids and brings them together and makes a protein. So, RNA makes protein. Now, proteins have a lot of functions in the cell. The basic function, one of the major functions of proteins are to act as catalysts. Proteins act as catalyst and I'm sure you know the catalysts are, as we've said before, matchmaker of the cell. They bring things together. So, you know, in order to really come up with a complex cellular biochemistry you couldn't rely on spontaneity. You couldn't rely on the fact that amino acid one and amino acid two are going to spontaneously over and over again form a bond to form a protein. You can't assume that different molecules are going to spontaneously bond without a catalyst.
So, you needed catalysts back then too. So, we're stuck here. DNA, too complex, catalyst, well if there's no DNA, there's no RNA. If there's no RNA there's no--unless could it be that the primitive births had RNA, its simpler component before DNA? Could RNA have been the true secret to the beginning of life? Wow, how cool would that be? A smaller, simpler molecule. Well, I've got to confess, I'm not the first one to think of that. Back in the 1970's Manfred Eigen did a very elegant project. What he was able to show was an interesting thing.
Now, let me tell you a little bit about RNA. RNA consists of these. Now, they're just letters to you, but to a molecular biologist these are exciting things. They're nucleotides. You could link over to the lecture on what RNA is made out of if you're really excited about this. What we find in RNA is that it is a combination of multiples of these nucleotides, cytosine, adenine, auricle, guanine. The sequence of these nucleotides will determine what protein RNA makes. Remember, DNA makes RNA, RNA makes protein. So the real question that I get asked is, "Could form RNA without the catalytic advantage of a protein?" Because remember, what do proteins do, they're the matchmakers. How are you going to get these C's and A's and U's and G's together if you don't have a protein to bring them together?
Talk about chasing your tail, but how are you going to get a protein to bring them together if you don't have RNA to make them? We can run around in circles all day long on this, but thanks to Manfred Eigen we don't have to run around in circles, because he did a great little experiment. He showed that indeed small portions of RNA can replicate. Let me tell you a little bit about how RNA replicates without going into too much detail. You see, there's this whole idea of base pairing and it's known and I don't want to tip my hat from the other lectures, but it's known that U will always bond to A and G will always bond to C. So, if you have a strand, like say this one here, U G C A U with the help of a catalyst, a lot of catalysts, what will happen is a U will bond with an A. A G will bond with a C, and G will bond with C and it will continue. In fact, you can get a lot of different strands.
So, what you can literally do is you can grow strands from other strands, but you need a catalyst for that, at least in our world you need a catalyst for it, but in Manfred Eigen's world he showed that you don't need to do this. Indeed, small pieces of RNA can be assembled from preexisting RNA. Now, where'd the preexisting RNA come from? Let's not forget Miller and Urey. These guys were able to show that you could get synthesis polymerization. You could get synthesis and Fox was able to show that you could get polymerization. So, we're already past that stage where we can get some crude RNA. We're at the point now was, can RNA replicate and holy mackerel it can. So, he got some small ones, but then he says, "You know, maybe there's other things that can act as catalyst except proteins." And he added some zinc.
He got 400 of these bad boys to link together. He got big pieces of RNA. He got big replications of RNA. This is big. He actually showed that RNA can form spontaneously and it can self-replicate. But wait a minute. That was then and this is now. Where's the catalyst? Eventually you had to get a catalyst. When was RNA going to start making proteins here? We don't have proteins yet and we all know that life runs by catalysis. Life runs by matchmaking, by proteins bringing things together.
Well, in 1981, vertiga. Watch what we're about to do here. You've heard about proteins acting as catalyst and I have to tell you that the name for catalyst, at least protein catalysts up until right now, is a group of molecules called enzymes. Well, in 1981 it was discovered that RNA can act as its own catalyst. You see, there's these procedures that RNA does once its made and we always suspected that when RNA was made, I'm talking about the 20^th century now not the hot thin soup, when RNA is made there's some editing that goes on. Chunks of that RNA are cut out and it was always assumed that a catalyst did this, proteins. Well, guess what was found. It was found that indeed RNA catalyzes itself. So, we have a term now. We're not going to be using enzymes to do this catalyses, we have discovered something new.
Ribozymes, RNA catalyst. Look what we have now. Look what we have. We now have a material, RNA, in this hot thin soup that can number one, reproduce. It can reproduce itself spontaneously. We have a material that we know by nature has the ability to bond to amino acids. That's the job of RNA. Now, we know RNA, hasn't changed, A G C and U still bond to amino acids, so now we have something that can also bond to amino acids. So, it bonds to amino acids. Acting like something might introduce one amino acid to another, sounds like a matchmaker to me. When it bonds to these amino acids it can also release them
So, now we have something that not only can reproduce, but it can make and produce chains of amino acids. It can make catalysts. Think about that. We have a mechanism to make proteins, which may catalyze reactions. We have a mechanism to make proteins, which can catalyze reactions. Is that interesting or what? Look at this. We have mechanisms, RNA, to assemble proteins and the proteins themselves can then go on and maybe they will be the catalyst. Well, obviously that's what happened. Well, what's going to happen if we're going to pop these things into a protobiont? Remember the protobiont is the shell? Well, let's pop them into a protobiont.
So, you know, let's talk about natural selection. Golly gee whiz, what's going to be selected for more? Protobionts, with RNA in there or RNA floating all over the place? The answer of course, is when this was incorporated into a protobiont what do we have? We have an organism that has the ability to make proteins and RNA, the first genetic sense of heredity. Cool stuff. Well, what happened next? You're going to have to take a look at the next lesson.
The Origin of Life
The Heterotroph Hypothesis: The First Genetic Material Page [1 of 2]

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