SCH2226 Lecture 9: Regulation of Gene Expression in Bacteria

Vocabulary flashcards covering the components, regulatory mechanisms, and mutations of the bacterial Lac Operon as discussed in SCH2226 Lecture 9.

Prokaryotes

Cells that do not have enclosed organelles such as nuclei, allowing all elements in the cell to be free to interact.

RNA Polymerase (in E.coli)

Consists of $2\, \alpha$, $1\, \beta$, $1\, \beta'$, and $1\, \omega$ subunits which binds a sigma factor to form a holoenzyme and recognizes the promoter site.

Transcription

The process of synthesizing an mRNA molecule from a DNA template strand using RNA Polymerase.

Translation

The process of synthesizing polypeptides or proteins from mRNA using ribosomes to connect amino acids.

Genetic Code

The 3 base code (CODON) through which RNA codes for amino acids; it is described as degenerate.

Operon

A functioning unit of genomic DNA containing a cluster of genes located together under the control of a single promoter and transcribed together.

Lac Operon

First discovered in 1940 by Jacob and Monod, it contains three genes involved in lactose metabolism and cell growth.

Lactose

A disaccharide made up of glucose and galactose joined by a $\beta-1\rightarrow 4$ glycosidic bond.

Lac Z

A gene in the lac operon that codes for $\beta$-galactosidase, which breaks down lactose into glucose and galactose.

Lac Y

A gene in the lac operon that codes for Galactose Permease, which actively transports lactose across the cytoplasmic membrane.

Lac A

A gene in the lac operon that codes for Thio-galactoside transacetylase.

Operator (lacO)

The binding site for the repressor molecule, consisting of a 22 base sequence.

Promoter (lacP)

The binding site for RNA Polymerase, featuring specific recognized areas at the $-35$ and $-10$ sites.

Lac I

The regulator gene that controls the production of the repressor protein.

Allolactose

A small sugar formed within the bacterial cell that acts as an inducer by binding to the allosteric site of the repressor protein.

Negative Control

Occurs when the binding of a protein prevents an event; in the lac operon, this is when the repressor binds to the operator to block RNA polymerase.

Positive Control

Occurs when the binding of a protein causes an event; in the lac operon, the binding of the CAP-cAMP complex stimulates RNA polymerase binding.

Catabolite Repression

A phenomenon where genes participating in the metabolism of other sugars are repressed when glucose is available.

CAP (Catabolite Activator Protein)

A protein that binds with cAMP to form a complex that stimulates the binding of RNA polymerase to the promoter.

lacOc Mutation

A constitutive mutation at the operator site that alters the DNA sequence so the repressor protein is no longer able to bind.

lacP- Mutation

A promoter mutation that interferes with the binding of RNA polymerase, preventing the production of lac proteins.

Constitutive Synthesis

Transcription that continues unchecked, often due to a mutation in the operator that prevents repressor binding.