Bio2051ch8.doc

Bio2051ch8.doc - lac operon e lac per mease transacetylase...

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Unformatted text preview: lac operon e lac per mease transacetylase (proteins) Chapter 8 Thursday, February 19, 2009 9:17 AM Chapter 8- T ranscription, T ranslation, and Bioinformatics RNA Synthesis Transcription- making an RNA copy of part of a DNA strand Differences between DNA & RNA: DNA- made of deoxyribonucleotides (has one less oxygen molecule than ribonucleotides) Double stranded Thymine Sugar = deoxyribose RNA- made of ribonucleotides Single stranded Uracil (instead of thymine) Sugar = ribose Three common types of RNA: mRNA Contains info to make proteins Only one that is translated into a protein tRNA Carries amino acids to build the polypeptide during translation 1. rRNN Component of ribosomes (site of protein synthesis) Template strand- DNA strand that is being copied into complementary mRNA RNA polymerase- enzyme that transcribes DNA into RNA Bacterial RNA polymerase 4 subunits: alpha (2 copies); beta ; beta' '; sigma Process of transcription 3 phases: Initiation Elongation Termination Transcript ion of RNA from DNA involves the enzyme RNA polymerase , which adds ribonucleotides onto 3' end of growing RNA chain Unlike DNA polymerase, RNA polymerase needs no primer RNA polymerase recognizes a specific start sequence on the DNA called the promoter and starts transcribing DNA into RNA at that site Promoter= transcription Transcription Initiation Sigma factor binds core RNA polymerase Forms RNA polymerase holoenzyme RNA polymerase binds promoter Sequence on DNA 10 and 35 bases upstream of start site Polymerase unwinds DNA at promoter Open complex Sigma factor released Promoters (sequence on DNA that RNA polymerase recognizes and binds to to start the process) Specific DNA sequences indicating start site of transcription Two important regions: (in Bacteria ) -35 sequence -10 sequence (Pribnow box) (- means upstream of start site) Prokaryotes have a single RNA polymerase with a sigma subunit. The sigma factor binds to the promoter to initiate transcription Multiple sigma factors S^70 Guides RNA polymerase to most genes ( housekeeping sigma)- most common S^32 Active when cell is stressed by heat Heat-shock response Transcription Elongation Core RNA polymerase moves down the template DNA strand from 3' to 5' RNA strand is made 5 to 3 (ribonucleotides are added to the 3' end) - complementary to the DNA Transcription Termination When RNA polymerase reaches terminator, transcription stops and RNA chain is released (not to be confused with terminus) Polymerase slows at pause site GC-rich sequence, forms stem loop Rho-dependent termination Rho (r) factor binds to mRNA Slides along mRNA to polymerase...
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This note was uploaded on 11/18/2010 for the course BIOL 2051 taught by Professor Brininstool during the Spring '07 term at LSU.

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Bio2051ch8.doc - lac operon e lac per mease transacetylase...

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