Test 3 Review Packet

Test 3 Review Packet - BISC1111 TEST 3 REVIEW PACKET GENE...

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BISC11Review-1 BISC1111 TEST 3 REVIEW PACKET GENE REGULATION: Operon: A unit of genetic function found in bacteria and phages, consisting of a promoter, an operator, and a coordinately regulated cluster of genes whose products function in a common pathway. Typ (Tryptophan) Operon : negative gene regulation - the trp operon is repressible because its transcription is usually on but can be inhibited when tryptophan bind allosterically to regulatory protein. - When tryptophan is absent : the repressor is inactive and the operon is on. RNA polymerase attaches to the DNA at the promoter and transcribes the operon's genes. - When tryptophan is present : the repressor is active and the operon is off. Accumulation of tryptophan inhibits its own production by activating the repressor protein, which binds to the operator, blocking transcription. Operator: Segment of DNA, or switch. Usually positioned within promotor, controls access of RNA polymerase to genes. inactive repressor: Can only bind to the operator when it is active, when not active the RNA polymerase continues to transcribe the genes. Activated by additon of tryp. trp repressor: Repressor binds to the operator and blocks attachment of RNA polymerase to the promoter, preventing transcription of genes. regulator gene: TrpR located some distance from operon it controls and has its own promoter. Expressed continuously. made from another DNA, has it’s own trpH gene that produces mRNA and creates inactive repressor. Corepressor: Small molecule that cooperated with a repressor protein to switch an operon off. Also required to activate repressor. Lac (Lactose) Operon : negative gene regulation
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CONTROL OF GENE EXPRESSION: Control of Gene expression: can occur at 4 different levels. 1. Histone modification: alteration of histones through various processes controls gene expression. Histones: Proteins around which the DNA is wrapped in nucleosomes Histone acetylation: Acetyl groups (-COCH3) are attached to lysines in histone tails. When acetylated, positive charges are neutralized and histone tails no longer bind to neighboring nucleosomes. Methylation: Addition of methyl groups (-CH3) promote condensation of chromatin. Phosphorylation: Addition of phosphate group to amino acid can unwind chromatin. Histone code hypothesis: Proposes that specific combinations of modifications, rather than the overall level of histone acetylation, determines chromatin configuration. Heterochromatin and euchromatin: Heterochromatin is bound and condensed while euchromatin is unwound due to acetylation and is able to be transcribed and produce RNA. Heterochromatin must undergo demethylation in order to become euchromatin. 2. Transcriptional Control: initiation of transcription is next major step of regulation after chromatin modification. -
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This note was uploaded on 02/01/2011 for the course BISC 1111 taught by Professor Brown during the Fall '10 term at GWU.

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Test 3 Review Packet - BISC1111 TEST 3 REVIEW PACKET GENE...

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