chapter 8

chapter 8 - Chapter 8- Transcription, Translation, and...

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Chapter 8- Transcription, Translation, and Bioinformatics (GOOD FIGURES) RNA Synthesis Transcription- making an RNA copy of part of a DNA strand. Differences between DNA & RNA: DNA- made of deoxyribonucleotides Double Stranded Thymine Sugar-deoxyribose RNA- made of ribonucleotides Single Stranded Uracil Sugar- ribose Three common types of RNA: 1. mRNA Contains info to make proteins 2. tRNA (transfer) a. Carries amino acids to build the polypeptide during translation 3. rRNA (ribosomal) a. 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) α, beta β, beta’ β’, sigma σ Process of transcription 3 phases: 1. Initiation 2. Elongation 3. Termination Transcription of RNA from DNA involves the enzyme RNA polymerase , which adds ribonucleotides onto the 3' ends 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. Transcription Initiation 1
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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 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. Sigma factor binds to promoter and tells polymerase where to start Multiple sigma factors S 70 Guides RNA polymerase to most genes (“housekeeping sigma”) Most commonly used S 32 Active when cell is stressed by heat. Heat-shock response: when a cell is stressed by high temperatures; this becomes active and different proteins are made to protect the cell 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. 2
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This note was uploaded on 10/11/2011 for the course BIOL 2051 taught by Professor Brininstool during the Spring '07 term at LSU.

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chapter 8 - Chapter 8- Transcription, Translation, and...

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