Microbiology

Bacterial Chromosome

A single, circular, double-stranded DNA molecule without histones or nuclear membrane, occupying the nucleoid region of the cytoplasm.

Essential Genome

The genes necessary for survival, including those for replication, transcription, translation, and core metabolism.

Accessory Genome

Includes plasmids, transposons, integrons, and prophages; carries genes that can provide advantages such as antibiotic resistance.

Plasmids

Small, circular DNA molecules that replicate independently of the bacterial chromosome, often carrying genes for antibiotic resistance or virulence.

R plasmids

Plasmids that carry multiple antibiotic resistance genes and can be transferred between bacteria.

Transposon (Tn)

Genetic elements that can move within and between genomes, often carrying resistance or toxin genes.

Integration of Prophage

The process by which a bacteriophage's genome integrates into the bacterial chromosome, potentially altering the host's characteristics.

Theta Intermediate

The shape formed during bacterial DNA replication where replication forks move bidirectionally from a single origin.

Helicase

An enzyme that unwinds DNA by breaking hydrogen bonds between the strands during replication.

DNA Ligase

An enzyme that joins Okazaki fragments together during DNA replication.

Operon Anatomy

Structure containing a promoter, operator, regulatory gene, and structural genes that controls gene expression in bacteria.

Inducible Operon

A normally off operon that is turned on in the presence of a substrate, typically involved in catabolic pathways.

Repressible Operon

A normally on operon that is turned off when its end product accumulates, typically involved in anabolic pathways.

Negative Control

A regulatory mechanism wherein a repressor protein binds to an operator to block transcription.

Positive Control

A regulatory mechanism wherein an activator protein enhances transcription by helping RNA polymerase bind to the promoter.

Allolactose

The actual inducer of the lac operon that binds to the repressor and prevents it from blocking transcription.

CAP-cAMP Complex

A regulatory complex that enhances the binding of RNA polymerase to the promoter of the lac operon under low glucose conditions.

Tryptophan

An amino acid that acts as a co-repressor in the trp operon, contributing to the regulation of enzyme production based on its availability.