Human Molecular Genetics - Regulation of Gene Expression in Bacteria

Flashcards covering the fundamentals of E. coli genetics, transcription, translation, and the specific molecular mechanisms of the lac operon.

Prokaryotes

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

RNA Polymerase (E. coli)

Consists of two alpha ($\alpha$), one beta ($\beta$), one beta-prime ($\beta'$), and one omega ($\omega$) subunits which bind a sigma factor to form a holoenzyme.

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.

Ribosomes

Complexes containing a $30S$ subunit and a $50S$ subunit that combine with transfer RNA to assemble polypeptide chains.

Codon

A three-base code in RNA used to code for specific amino acids.

Operon

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

Lac Operon

First discovered in 1940 by Jacob and Monod, this inducible unit contains three genes (Lac Z, Lac Y, and Lac A) involved in lactose metabolism and cell growth.

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, though its specific function is not currently known.

Operator (lacO)

A 22 base sequence (5’-GAATTGTGAGCGGATAACAATT-3’) on the DNA strand that acts as the binding site for the repressor protein.

Promoter (lacP)

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

lacI

A regulatory gene that controls the production of the lac repressor protein.

Inducer

A molecule (like lactose or allolactose) that binds to the repressor, causing a conformational change that prevents the repressor from binding to the operator.

Lactose

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

Allolactose

A sugar formed within the cell when lactose is present that acts as the inducer by fitting onto the allosteric site of the repressor protein.

Constitutive Synthesis

Transcription that continues unchecked due to mutations, such as those in the operator ($lacO^c$), where the repressor cannot bind.

lacP- mutation

A mutation at the promoter site that interferes with the binding of RNA polymerase, acting as a suppressive mutation.

Positive Control

Regulation where the binding of a protein (such as CAP-cAMP) causes an event, like stimulating the binding of polymerase.

Negative Control

Regulation where the binding of a protein (such as the lac repressor) prevents an event, like blocking the binding of RNA polymerase.

Catabolite Repression

A type of positive control where the presence of glucose represses the metabolism of other sugars.

CAP (Catabolite Activator Protein)

A protein that binds with cAMP to form a complex that binds near the promoter to stimulate RNA polymerase binding when glucose is absent.