MCB 121 Lecture 8

MCB 121 Lecture 8 - MCB 121 Lecture 8 MT 1 mean 94.5 ~ 63...

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MCB 121 - Lecture 8 MT 1 mean: 94.5 ~ 63%, highest is 137/150. Overview of Gene Expressions I. Bacteria II. Type 1 III. Type 3 IV Type 4. Central Process of Gene Expression Genes are made of DNA: DNA (transcribed by RNA polymerase) => RNA (process RNA in many different ways) => mRNA, tRNA, rRNA, and other - final products of gene expression(translation) => Proteins (translated from mRNA) ** tRNA and rRNA are functional RNA Nomenclature with respect to transcription: - Transcription bubble: where transcription occurs along the ss DNA - RNA polymerase (RNA pol): its size is bigger than transcription bubble * Bubble is inside the RNA pol - sense strand (coding strand): strand equivalent to strand codes for proteins (same as mRNA) - non-sense strand (anti-sense or template strand): it's the template for mRNA RNA is synthesized in 5' to 3' direction!!!!!!!!!!!!!!!! - RNA is the same sequence at the top strand of DNA and complementary to the bottom strand of DNA - 5' end of the gene corresponds to the 5' end of the mRNA - 3' end of the gene corresponds to the 3' end of the mRNA (according to the sequence of mRNA) - RNA polymerase copies 3' to 5' of the template strand and release mRNA from 5' to 3' - different genes can go different directions (each chromosomes can have multiple anti-sense strands and sense strands), depends on the regions of chromosome. ----------------------------------------- BACTERIA - E.Coli - only 1 RNA polymerase that transcribes all kinds of RNA (mRNA, tRNA, and rRNA)
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- the RNA polymerase consists of 2 alpha subunits and a beta subunit, a beta' subunit, and + sigma * α 2 ββ' (core polymerase- can polymerize and make RNA) + σ (necessary for initiation) RNA polymerase bring the sigma factor along to bind to DNA - sigma factor has to be released from RNA polymerase in order for RNA polymerase to start the polymerization. No all parts of genome are transcribed, only the genes are transcribed! - promoter : binding site of RNA polymerase in bacteria * contains consensus sequences at certain base location ** there are the most frequent nucleotides at this position in different promoters * but there is still variation * promoter contains the consensus sequences is the strongest promoter ** this is how bacteria regulate the level of different proteins - Operator : where regulatory factors bind * can be either positive (activate the gene expression) or negative (repress the gene expression) * example of negative: repress gene expression by having operator region overlap with the promoter = repressor bind to operator would block the polymerase binding to promoter = such as lac repressor binds to lac operator to block the polymerase - Transcription terminato r: in order to stop transcription of a gene so gene has downstream has its own regulator. * normally has structure called
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MCB 121 Lecture 8 - MCB 121 Lecture 8 MT 1 mean 94.5 ~ 63...

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