Operons: Lac and Trp

Flashcards covering key vocabulary terms related to the Lac and Trp operons, including their structure, regulation, and related concepts like catabolite repression and attenuation.

Operon

Set of genes transcribed from one promoter.

Promoter (Operon Structure)

Where RNA polymerase binds.

Structural Genes (Operon Structure)

Genes transcribed by the promoter.

Operator (Operon Structure)

Location where repressors and activators bind; can overlap with promoter or be downstream.

Negative Transcriptional Control

Binding of regulatory protein at operator inhibits initiation of transcription; mRNA expression is reduced.

Repressor proteins

Exist in active and inactive forms; inducers/corepressors alter activity of repressor by binding.

Positive Transcriptional Control

Binding of a regulatory protein at an operator promotes transcription initiation; mRNA synthesis is increased.

Activation

Inactive protein is activated by inducer; active protein is inactivated by inhibitor.

LacZ

β-galactosidase - Used to make genes to eat lactose.

LacY

Permease to allow lactose into cell.

LacA

Acetylates (function not fully known).

LacI

Repressor for the lac operon.

Allolactose

Binds repressor, preventing it from binding to the operator in the lac operon.

Diauxic Growth

A biphasic growth pattern involving preferential use of one carbon source over another.

Catabolite Repression

Regulation of transcription by both repressors and activators; plays a role in diauxic growth.

Catabolite Activator Protein (CAP)

Also called cyclic AMP receptor protein (CRP); brings about coordinate regulation of catabolite operons.

cAMP

3’,5’-cyclic adenosine monophosphate; when bound to CAP, CAP is in active form.

Attenuation

Transcription regulation by controlling transcription termination, first demonstrated with trp operon.

Trp Operon

Consists of 5 structural genes coding for enzymes needed to synthesize tryptophan; negative transcriptional control.

Trp Repressor

If trp is present, it binds the repressor to activate it; binds at the operator to block transcription.

TrpL

Leader peptide in attenuation; encodes for many trp amino acids; contains stem-loop secondary structures.

Riboswitches

Folding of mRNA leader sequence determines if transcription will continue/terminate; folding altered in response to mRNA binding of an effector molecule.