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美国生物学课堂录像-1
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我找到了美国生物学的课堂录像，看看大家是不是需要 虫子们反映6有问题，我已经重新上传，看看是不是有问题。 http://www.divshare.com/download/843667-a7e [ Last edited by whyerect on 2007-6-11 at 06:08 ] |
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这里还有对应的文本内容 Good morning class! Ah… I just want to spend the first couple of minutes clearing up 3 issues not as a major conceptually issue but we like to focus on details and get them right…uh get them correct here as well. Firstly I…uh…I misdrew a reaction last time that described why RNA is alkaline *. IE if we have high pH we call that alkali pH, or the alkaine pH actually to use the adjtive, and we said the hydroxial groups can cause the cleavage of the phosphodioxy bonds of RNA but not DNA. And when I described that happening is that the alcali group causes the formation of this 5 memberd ring right here, 2 carbons, 2 oxygens and a phosphate and that results eventually to this where there is no longer any connection, with a ribonucleoside monophosphate below, and I drewed like this without an oxygen, and that’s nono, because, in fact, in truth, un, and as many of you picked up, this reverts to a two-prime *. So please note there is a mistake there. Um, there’s also a couple of other mistakes, for example in the textbook, it says, it gives the impression that if you polymize nucleic acids, you use a monophosphate to do so. And if you listened my lecture last time, that doesn’t make any sense. Because you need to invest the energy of triphosphate in order to create enough energy to generate enough energy for polymerization. The textbook is incorrect there, the textbook are written by people for better or worse and such like everything else they are er, mortal and fallible. So the truth of the matter is when you’re polymerizing DNA or RNA, you need one of the four ribonucleoside or deoxyribonucleoside triphosphrate in order to donate the energy that makes possible this polermization. And please note that there's a mistake in the book. Recall as I said last time, the fact that ATP is, is really the, the currency of energy in the cell, and that its energy is stored in this coiled* in this pent-up spring, with the elec, nutral-elec prepulsion between the three negatively charged phosphate, carry within it the enormous potential energy and some of that potential energy can be realized during the synthesize polymization of nucleic acids, like living this bond here, one can also generate potential energy by living this bond here. This is the α-, the β-, and the γ-phosphate, and cleavage of either can create substantial energy which in turn can ,as we will indicate shortly, be invested in other reactions, the reaction of polymerization. A second point I’d like to make to you is the following units. you’d say it’s kind of coincidence. The currency of energy in the cell is ATP, Adenosine Triphosphate, we see its structure here, and this happens to be one of the four purine courses of the RNA. So this molecule is used in this two different ostensively unrelated applications, one to polymerize to make RNA where genetic information is stored and conveyed, or alternatively it’s used here in this context, um, in, in order to, uh, serve as a currency for, for energy, high energy is ATP.ADP with a little lower energy ,AMP, monophosphate with even lower energy. And you might ask yourself scratch at why don’t say why this same molecule is used for this two different things. In fact, there yet other applications of…uh… this ribonucleoside which also seems to be unrelated to the storage or the conveyance of genetic information, and it is believed probably correctly the reason why the same molecule is used for this totally different applications is that early in the evolution of life on this planet, there really were a rather small number of biological molecules that existed, indeed as we will mentione again later,it’s probably the case the first organism didn’t use NDA as genoms. It’s an article of faith for us that once the story genetic information in DNA molecules and I implied that quite explicitely last time, but the fact of the matter is it’s probably the case that the first organism, the first pre-cellular life forms use RNA as an genetic material. RNA can storage things. Replicating RNA via double strand RNA molecules as a way of a alkide genetic information. |
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