BIO325 - Lecture 6

BIO325 - Lecture 6 - BIO325 January 31, 2008 DNA...

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BIO325 January 31, 2008 DNA Transcription (cont.) RNA Processing I. DNA Transcription (cont.) a. Transcription in Prokaryotes (cont.) i. E. Coli lac gene promoter 1. Spacing close to idealized promoter in E.Coli 2. Consensus sequence is: TTGACA, TATAAT a. Change: 1, 2 respectively in -35 and -10 3. Promoter still works 4. Biggest change in -10 promoter, biggest slowdown for initiation in transcription is there because biggest change from consensus sequence a. Unwinding very slow b. Very little transcription possible here c. = Weak promoter d. N.B. Strong promoters are recognized by almost matching consensus sequences 5. Weak v. Strong promoters a. Why? i. Needing more of some gene products and less of others ii. Time 1. Strong promoter – gene product will be needed by cell under most circumstances, commonly needed 2. Weak promoter – gene product isn’t needed at higher level very often b. Promoter is promoter, can’t change strength on whim, “default setting” i. “lot of transcription” v. “very little transcription” ii. Elongation 1. Sigma factor not needed for elongation, not present a. Dissociates and core enzyme starts progressing 2. Protein will bind to core enzyme in place of sigma factor NusA a. Function: Slows down RNA pol 3. Transcription and Translation are coupled in prokaryotes – function simultaneously a. Happen on same mRNA molecule at same time b. While RNA pol adds bases, ribosome starts translatingP
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c. RNA pol is faster than ribosomes i. Gap is formed between RNA pol and ribosomes ii. Ribosomes shield mRNA from being attacked and broken down by enzymes d. Better that transcription and translation be closely coupled, NusA slows down transcription of RNA pol iii. Termination 1. Two different types a. Rho-dependent i. Code proteins b. Rho-independent c. Depending on whether or not Rho protein is
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This note was uploaded on 04/22/2008 for the course BIO 325 taught by Professor Saxena during the Spring '08 term at University of Texas.

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BIO325 - Lecture 6 - BIO325 January 31, 2008 DNA...

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