Learning Objective

Explain the structure, organization, gene content, and functional significance of the bacterial chromosome, including its circular nature, loop arrangement, gene number, and role as the location of all essential genes.

Bacterial Chromosome

• Most bacteria possess a single chromosome, though multiple copies of that chromosome can exist in each cell.
• The chromosome is a large, covalently closed, circular, double-stranded DNA molecule.
• DNA is organized into supercoiled loops, anchored to a proteinaceous central core.
• A single-strand topoisomerase introduces one nick that relaxes only the loop being transcribed or replicated.
• The typical bacterial chromosome encodes ~2,000 genes.
• All essential genes required for survival are located on the chromosome (not plasmids).

Activity