MBG 2040 Chapter Notes - Chapter 18: Gene Expression, Corepressor, Repressor
3 Dec 2017
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Induction alters the rate of enzyme synthesis, not the activity of existing enzyme molecules: a gene whose expression has been turned off in this way is said to be. Repressed ; the process is called repression: when the expression of this gene is turned on, it is said to be depressed ; such a response in called depression, enzymes that are components of anabolic pathways often are repressible. In prokaryotes, genes that specify housekeeping functions such a rrnas, trnas, and ribosomal proteins are expressed constitutively. In a negative, inducible control mechanism, the free repressor binds to the rpbs and prevents the transcription of the structural gene in the absence of inducer. In a negative, repressible regulatory mechanism, transcription of the structural gene occurs in the absence of the co-repressor, but not in its presence. Key points: gene expression is controlled by both positive and negative regulatory mechanisms.
