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chapter8 - Chapter 8 Transcription Translation and...

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Chapter 8- Transcription, Translation, and Bioinformatics RNA Synthesis Transcription- making an RNA copy of part of a DNA strand Differences between DNA & RNA: DNA- made of deoxyribonucleotides Double-stranded Thymine (RNA does not have) Sugar-deoxyribose RNA- made of ribonucleotides Single-stranded Uracil (Unique to RNA) Sugar-ribose Three types of RNA: 1. mRNA Contains information to make proteins 2. tRNA a. Carries amino acids to build the polypeptides during translation 3. rRNA a. Component of ribosomes (site of protein synthesis) Template strand- DNA strand that is being copied into complementary rRNA…. Because of complementary base pairing, only one strand of DNA will be copied into RNA at a time RNA polymerase- enzyme that transcribes DNA into RNA Bacterial RNA polymerase 4 subunits: alpha, beta, beta prime, sigma Process of transcription 3 phases: - Initiation - Elongation - 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 1
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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 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 sing 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 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 2
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Transcription Termination When RNA polymerase reaches terminator, transcription stops & RNA chain is released.
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