341lecture12oct5sakai

341lecture12oct5sakai - Cell Biology 341 Last lecture:...

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Cell Biology 341 Monday, October 5, 2009 Today: Initiation of translation in procaryotic cells versus eucaryotic cells Steps in translation of mRNA on a ribosome Begin chapter 7 on control of gene expression Bring two #2 pencils to the exam this Friday, Oct 9 Office hours this week: Tues 10-noon, Thurs 2-4 pm Last lecture: Jmol presentation of TATA-binding protein interactions with DNA Many eucaryotic primary transcripts can be spliced in alternative ways to yield more than one type of mRNA, each encoding a different polypeptide product Translation of mRNA into protein: 20 different aminoacyl-tRNA synthetases catalyze the covalent addition of amino acids to the 3′-end of tRNA at the cost of ATP → AMP + 2 P i Ribosomes are rRNA/protein complexes composed of large and small subunits There are three binding sites for tRNA: A, P and E sites
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Initiation of translation The small subunit of the ribosome binds the mRNA and sets the reading frame A mistake would cause a nonsense protein Initiation is an important point of regulation of protein synthesis, controlling the rate of protein synthesis Translation always begins with the methionine codon AUG, and a special initiator tRNA for methionine In procaryotes, the small subunit rRNA basepairs with the ribosome-binding sequence of the mRNA a few nucleotides upstream of the AUG In eucaryotes, the small subunit of the ribosome binds the 5' cap and scans to the first AUG in the sequence 5′- ACCAUG G-3′ Initiation factors assist with binding and recognition
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Comparison of procaryotic and eucaryotic mRNAs Figure 6-22
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341lecture12oct5sakai - Cell Biology 341 Last lecture:...

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