MICRO CH8 - 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 Nitrogen base thymine found in DNA but not RNA Sugar- deoxyribose RNA- made of ribonucleotides Single stranded Uracil instead of thymine Sugar- ribose 3 main types of RNA: 1. Messenger RNA (mRNA) - Encode proteins - Average 1000-1500 bases long 2. Transfer RNA (tRNA) - Carries amino acids to the ribosome to build a protein during translation 3. Ribosomal RNA (rRNA) - 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 by adding ribonucleotides onto 3’ end of growing RNA chain Needs no primer Recognizes specific start sequence on DNA called the promoter & starts transcribing DNA into RNA at that site Bacterial RNA polymerase - 4 subunits: alpha (2), beta, beta prime, and sigma - σ function is to help core enzyme locate promoter (beginning of gene) Multiple sigma factors   (over 100 known so far from numerous species) Sigma 70 “housekeeping” sigma factor used for most essential genes 1
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Sigma 32 Active when cell is stressed by heat (heat-shock response) Process of transcription 3 phases: 1. Initiation 2. Elongation 3. Termination 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 (on DNA before transcription site starts Polymerase unwinds DNA at promoter Open complex 1 st ribonucleotide base pairs to DNA at +1 position Transcription Elongation Sigma dissociates after about 9 bases have been joined Core RNA polymerase moves down the template DNA strand RNA strand is made 5’ to 3’( ribonucleotides added to 3’ end ) about 45 bases/second- complementary to the DNA Transcription Termination When RNA polymerase reaches terminator, transcription stops and RNA chain is released 2 known transcription termination sequences in bacteria : Rho-dependent termination Rho ( r ) factor binds to mRNA Slides along mRNA to polymerase breaks Rho independent
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This note was uploaded on 02/23/2012 for the course BIOL 2051 taught by Professor Brininstool during the Fall '07 term at LSU.

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MICRO CH8 - Chapter 8- Transcription, Translation, and...

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