Chapter31

Chapter31 - BCH 4054 Chapter 31 Lecture Notes Slide 1...

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Chapter 31, page 1 BCH 4054 Chapter 31 Lecture Notes Slide 1 Chapter 31 Transcription and Regulation of Gene Expression Slide 2 Messenger RNA • Central Dogma (Francis Crick, 1958) • DNA RNA Protein (Fig 31.1) • Jacob-Monod Hypothesis: Four properties • Base composition reflecting DNA • Heterogeneous in size • Can associate with ribosomes • High rate of turnover Early labeling experiments showed ribosomes as the site of protein synthesis. An alternate hypothesis was that each protein had its own specific ribosome where it is made. Slide 3 Other Forms of RNA • Ribosomal RNA • Major RNA component of cell • Transfer RNA • Small RNA molecules carrying the amino acids in protein synthesis • Eukaryotic “small nuclear” RNA • mRNA processing in eukaryotes • Viral RNA All forms are made by copying a DNA template (excepting some RNA viruses), so the process of transcription is common to all.
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Chapter 31, page 2 Slide 4 Transcription, General Features A “template” DNA strand is copied using the Watson Crick base pairing rules • See Fig Page 1016 for nomenclature convention • Only small segments of DNA copied at any one time. • Must be specific start and stop sites • Copying must be regulated • Chemistry is similar to that of DNA polymerase • Nucleoside triphosphates add to 3’ OH end with pyrophosphate as the product. Slide 5 Transcription, General Features, con’t. • DNA separates and forms a “transcription bubble” • No 3’-5’ proofreading, so error rate is about 1 in 10 4 • Topoisomerases needed to introduce negative supercoiling in front, remove it in rear • Otherwise RNA would end up wrapped around the DNA (See Fig 31.6) Slide 6 Transcription in Prokaryotes • A single polymerase α 2 ββ σ structure β ’ binds to DNA, β binds substrate NTP’s σ recognizes start site, called the promoter • Several different σ ’s, recognizing different promoters • Not required for RNA synthesis; dissociates after transcription starts, leaving
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Chapter 31, page 3 Slide 7 Stages of Transcription in Prokaryotes • Binding of Polymerase at promoter site • Initiation of polymerization • Chain elongation • Chain termination • (See Fig 31.2) Slide 8 Transcription in Prokaryotes: Binding Closed promoter complex formed • K d is 10 -6 to 10 -9 M • Polymerase unwinds DNA to form open promoter complex • K d is ~ 10 -14 M • Promoter sites characterized by DNA footprinting • See Fig page 1018 Slide 9 Prokaryotic Promoter Sites • About 40 bp region on the 5’ side of the transcription start site • Two consensus sequence elements • “-35 region”, consensus TTGACA • Binding site for σ subunit • Pribnow box near –10, consensus TATAAT • Easier to unwind DNA • See Fig 31.3 Different σ units recognize different promoter sites. For instance, “heat shock” proteins are recognized by a specific σ unit. Not all variation in rate is due to
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This note was uploaded on 05/22/2011 for the course BCH 4054 taught by Professor Logan/gilmer during the Spring '06 term at FSU.

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Chapter31 - BCH 4054 Chapter 31 Lecture Notes Slide 1...

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