GENE 3200 Midterm: Prokaryotic Learning Objective

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19 Feb 2019

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Basic lo: be familiar with the structure of a prokaryotic operon, in particular lac and trp operons, lac operon can be positive, negative, repressible, and inducible. If the signal (tryptophan) is present, expression is repressed. (negative repressible system) levels of tryptophan control gene expression. The higher tryptophan levels- less likely to be expressed. If tryptophan is present, tryptophan interacts with the inactive trpr repressor making trpr active. The repressor binds to operator and expression stops. Enzymes levels decrease, tryptophan levels decrease as well, so bacteria want to increase production. It does this when the active repressor releases and is inactive. Inducer- induces expression, transcription occurs. (signal such as lactose: co-repressor- binds to repressor to activate it, tryptophan is a co-repressor for trp2 (inactive repressor) (check)*** Differential gene expression: some genes encode products that are always needed (aka constitutive genes (continually expressed)) and some genes encode products that only are needed at certain times or in certain circumstances (regulated expression))

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