Final Exam Review biochem1

Final Exam Review biochem1 - Final Exam Review! (FUCK FUCK...

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Unformatted text preview: Final Exam Review! (FUCK FUCK FUCK) I. Regulation of Transcription a. Prokaryotes have naked DNA so transcription is always on by default (DNA is always available/accessable b/c its naked) & protein factors typically REPRESS transcription at most promoters [ex. Lac] b. Eukaryotes have DNA-histone complexes, and as a result transcription is off by default since DNA unavailable due to histone complex & most transcription factors act as ACTIVATORS [ex. SWI/SNF, NURF] II. Regulation of Prokaryotic Gene Expression a. Early studies with lac promoters were instrumental for gaining understanding of transcription regulation in bacteria. b. The lac promoter is flanked on both sides by 2 conserved elements {Oe and Oi} at which the lac repressor protein binds. Receptor/unique molecule can bind lactose. c. Lac repressor protein loops DNA (in promoter region), preventing RNA polymerase/promoter interaction. Small CRP protein can bind inside the loop but RNA polymerase cannot fit. LacI repressor/lactose compolex loses affinity to Oe and Oi then dissociates from promoter turning on transcription d. 1) When theres NO lactose in the growth medium, E. coli cell does not express Lac genes (No transcription at lac operon) 2) When there IS lactose in the growth medium, transcription at lac promoter switches on and E. coli cell produces enzymes needed for utilization of lactose III. TRANSLATION: protein synthesis (Know schematic from txt book) a. In bacteria translation is coupled with transcription b. EUKARYOTIC mRNA modifications i. Splicing-some parts are excised and remaining fragments joined together [by spliccosomes] ii. Capping- methylated G ppp pos 7 or A ppp at 5 terminus [by capping enzyme] iii. Polyadenylation at 3 terminus [by poly(rA) polymerase]-mostly in euk. But approx. 10% of bacterial cells are polyadenylated. iv. Nucleases can trim transcribed RNA- this is in both euk/prok c. mRNA transmits info present in DNA (eukaryotic) i. eukaryotic are almost always monocistronic ii. 5 terminus of Euk. mRNA is capped w/7-methylguanosine linked through a 5 triphosphate bridge to the 5 end of the messenger sequence iii. A 5 non-translated region (which may be few hundred nucleotides long) separates the cap from the translation initiation signal (usually AUG ). d. Prokaryotic mRNA i. Differs from the eukaryotic mRNA in that the 5 end IS NOT CAPPED but retains a terminal Triphosphate from initiation of its synthesis by RNA polymerase ii. Also, they are polycistronic and include > 1 AUG initiation sequence iii. A ribosome-positioning sequence is located about 10 nucleotides upstream of a valid AUG initiation signal (2 recognition factors) 1. one recognition factor: SHINE-DALGARNO element: a conserved sequence typically found @ the 5 non translated part of mRNA, Short (8-10 nucleotides in length), G/C rich sequence, and can hybridize with rRNA increasing affinity of the DNA to the ribosome 2. Some mRNAs which are efficiently translated do not have SDE...
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This note was uploaded on 04/09/2011 for the course CHEM 4461 taught by Professor Max during the Spring '08 term at Lamar University.

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Final Exam Review biochem1 - Final Exam Review! (FUCK FUCK...

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