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BIO152H5 (140)
Chapter 16

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Fiona Rawle

Chapter 16 Notes Transcription RNA Processing and TranslationThe strand that is read by the enzyme RNA polymerase is called the template strand The other strand is called the nontemplate strand or coding strand Nontemplate strands sequence matches the sequence of the RNA that is transcribed from the template strand and codes for a polypeptideCoding strand and RNA dont match exactly because RNA has uracil U rather than the thymine T found in coding strandAdenine A in the DNA template strand specifies a U in the complementary RNA strandRNA polymerase performs a templatedirected synthesis in the 5 to 3 direction But it does not require a primer to begin transcription Bacterial RNA polymerase and sigma form a holoenzyme A holoenzyme consists of a core enzyme which contains the active site for catalysis and other required proteinsPromoters Sections of DNA where transcription beginsSigma appeared to be responsible for guiding RNA polymerase to specific locations where transcription should begin When analyzed the base sequence of promoters from various bacteria and viruses that infect bacteria found that promoters were 4050 base pairs long and had a section in common a series of bases identical or similar to TATAAT This sequence is known as 10 box because it is centered about 10 bases from the point where bacterial RNA polymerase starts transcriptionDNA located in the direction RNA polymerase moves during transcription is downstream from the point of reference DNA located in opposite direction is upstream The 10 box is centered about 10 bases upstream from transcription start site Place where transcription begins is called the 1 siteSequence of TTGACA occurred in these same promoters and was centered about 35 bases upstream from 1 site This sequence is called the 35 boxEukaryotic genes have promoters and signal where transcription should begin just as bacteria but more complex and diverseMany of the eukaryotic promoters include a unique sequence called a TATA box centred about 30 base pairs upstream of the transcription start siteSigma and not RNA polymerase makes the initial contact with DNA that starts transcription This shows the hypothesis that sigma is a regulatory protein Sigma tells RNA polymerase where and when to start synthesizing RNA
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