lecture12 - LECTURE 12 21 September 2009 (P. J. Hollenbeck)...

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LECTURE 12 21 September 2009 (P. J. Hollenbeck) BIOL231 The Genetic Code and Protein Translation Read: Chap. 7, pp. 243-256; study DVD 7.4, 7.5 Probs: 31-35 + Exam III, '03, #3; Exam III, '05, #2 I. Information flow (A) You already know the “central dogma” of molecular genetics, that DNA => RNA => protein, with limited exceptions (one is the “reverse transcription” of retroviral RNA into DNA). And you have seen diagrams like this one: DNA: 3' - GTG GTA CAA AAG TAC TGC GAA - 5' 9 (Transcription) 9 RNA: 5' - CAC CAU GUU UUC AUG ACG CUU - 3' 9 (Translation) 9 protein: N - his his val phe met thr leu – C Today let’s figure out in more detail what this means. .. (B) Transcription vs translation. “Transcription” and “translation” mean, in biology, pretty much what they mean in the English language. Transcription is the conversion of information from one form to another (i.e., written to spoken, as a court reporter does) without changing languages. Translation is the conversion of information between two different languages. In our cells, transcription copies information from DNA to RNA, keeping it in the language of nucleic acids. Translation copies information from RNA to protein, converting the information to a totally different molecular language. How? II. The code for translating RNA into protein (A) Codons & degeneracy (1) There are just 4 bases in DNA and RNA, but 20 common amino acids. This allowed George Gamow, among others, to predict (long before the code was cracked) that each amino acid in a protein must be specified by a set of 3 bases. That is because 4 = 16 2 (too few), while 4 = 64 (enough, in fact, more than necessary). The “more than 3 necessary” part means that each amino acid can in principle be encoded by more than one set of 3 bases. This kind of code – in which one set of elements does NOT map uniquely into another set – is called a DEGENERATE code. With 64 base triplets available to encode just 20 amino acids, we say that the genetic code is highly degenerate.
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This note was uploaded on 12/18/2009 for the course BIOL 101 taught by Professor Wormer during the Fall '08 term at Purdue University-West Lafayette.

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lecture12 - LECTURE 12 21 September 2009 (P. J. Hollenbeck)...

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