4 - Molecular Cell Biology 32 Professor Andrew Wurmser...

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Molecular Cell Biology 32 Professor Andrew Wurmser 9/06/07 Lecture 4 Sharing or distribution of lecture notes, or sharing of your subscription, is ILLEGAL and will be prosecuted. Our non-profit, student-run program depends on your individual subscription for its continued existence. These notes are copyrighted by the University of California and are for your personal use only. Sharing or copying these notes is illegal and could end note taking for this course ANNOUNCEMENTS Office hours will be held from 2-4 pm on Friday in 491 LSA. If we get too many students we’ll have to make other arrangements. We have a new GSI, Jason, so 111 and 112 discussion sections can resume next week. LECTURE Review Today we’ll start by addressing some questions I’ve received from students. We talked about the double-stranded DNA helix and that it is the medium that encodes for all the proteins in the cell. The backbone is composed of sugar and phosphate. Attached to the sugar phosphate backbone are bases which all combine to form a double-stranded DNA double helix. We talked about how DNA makes RNA which in turn makes protein. The antisense strand of the DNA double helix is the one that does not serve as an mRNA template. The other strand is the sense strand . It is this strand that serves as the template for the complementary mRNA molecule. The end that starts with phosphate is the 5’ and the end that starts with the sugar is the 3’ . The 5’ end does not contain codons and is therefore not converted into proteins. Only the coding sequence of the mRNA contains codons that serve as the template for proteins. There are other regions on either side of the coding region of the mRNA molecule that serve various functions other than transcription. The poly-A tail dictates the stability of the mRNA molecule. The only RNA that encodes for proteins is mRNA. One of the unique properties of tRNAs is that there are sequences of complementary base pairs in every tRNA molecule. There is a piece of the 5’ end that is complementary to a piece close to the 3’ end. In between these extreme poles there are other complementary base regions that allow tRNA to fold onto itself, creating the three-dimensional model that we are familiar with. This complementary base pair folding allows for stability in the tRNA molecule. The 5’ and 3’ ends function to bind specific amino acids. Each amino acid is coupled to a specific tRNA molecule. The other end, the anticodon end of the tRNA molecule, binds to the codon of the mRNA molecule during translation. We discussed last time that covalent bonds form between amino acids during the process of translation. Remember that ribosomal RNA composes ribosomes. Also remember that miRNA (micro RNA) are short non-coding RNA molecules that bind to the 3’ region of mRNA and destabilize mRNA, preventing translation of mRNA to tRNA. RNAi (RNA interference) is a form of artificial RNA that is created in the lab and functions just like miRNA to silence transcription.
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4 - Molecular Cell Biology 32 Professor Andrew Wurmser...

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