HMG - Week 12: Gene Expression in Bacteria LO

Vocabulary-style flashcards covering the mechanisms, structural components, and regulatory control of the bacterial lac operon based on the Week 12 HMG lecture notes.

Gene Regulation

A process allowing bacteria to only produce proteins when needed, helping to save energy, conserve resources, and respond quickly to environmental conditions.

Nucleoid

The region in a prokaryotic cell where the circular chromosome is located, since there is no nucleus.

Coupling of Transcription and Translation

An important feature in bacteria where translation begins before transcription has finished because there is no nucleus separating the processes.

RNA Polymerase Holoenzyme

A complex in E. coli consisting of $2 \alpha$, $1 \beta$, $1 \beta'$, and $1 \omega$ subunits, plus the sigma ($\sigma$) factor that recognizes promoters.

70S Ribosome

The complete bacterial ribosome formed by the union of a $30S$ small subunit and a $50S$ large subunit.

Codon

A sequence of three nucleotides that specifies a particular amino acid, such as AUG for Methionine.

Degeneracy

A property of the genetic code where multiple different codons may code for the same amino acid, such as the six different codons for Leucine.

Operon

A cluster of genes controlled by a single promoter and transcribed together as one mRNA molecule.

Regulatory Gene

A component of an operon that produces a regulatory protein, such as a repressor.

Promoter (lacP)

The binding site for RNA polymerase that functions to initiate transcription.

Operator (lacO)

The binding site for repressor proteins that acts as a molecular ON/OFF switch for the operon.

Structural Genes

Genes within an operon that encode proteins involved in a specific biochemical pathway.

lacZ

A structural gene that encodes $\beta$-Galactosidase, which breaks lactose into glucose and galactose and converts lactose into allolactose.

lacY

A structural gene that encodes Lactose Permease, a membrane transport protein that imports lactose into the cell.

lacA

A structural gene that encodes Transacetylase, thought to assist in detoxifying certain compounds.

lacI Gene

A gene located upstream of the operon that produces the Lac Repressor protein.

Negative Control

Regulation that occurs through the action of a repressor protein; in the lac operon, this occurs when lactose is absent and the repressor blocks RNA polymerase.

Allolactose

The true inducer of the lac operon which binds to the repressor, changing its shape so it can no longer bind to the operator.

Tetramer

The molecular structure of the lac repressor, meaning it consists of four protein subunits joined together.

lacI⁻ Mutation

A mutation that produces a defective repressor protein that cannot bind the operator, resulting in constitutive (permanent) expression of the operon; it acts in trans.

lacOᶜ Mutation

An 'Operator Constitutive' mutation in the DNA sequence that prevents the repressor from binding, leading to permanent transcription; it acts in cis.

Positive Control

Regulation mediated by glucose availability; when glucose is low, cAMP levels increase and bind to CAP to stimulate transcription.

CAP-cAMP Complex

A complex that binds to DNA when glucose levels are low, increasing RNA polymerase binding and greatly increasing transcription.

Inducible Operon

A type of operon, such as the lac operon, that is typically off but can be turned on in the presence of an inducer like allolactose.

Maximum Lac Operon Expression

The state achieved only when lactose is present (to remove the repressor) AND glucose is absent (to allow CAP-cAMP binding).