12. Prokaryotic genome and regulation of gene expression.
Covers the bacterial chromosome and plasmids, including the nucleoid, origin and terminus, and how genes are grouped into operons. Explains transcription initiation, promoter elements with the sigma factor, and operon examples (curli, lac, tryptophan) and sporulation. Ends with Rho-dependent and Rho-independent transcription termination, with a note on the hairpin mechanism.
Topic 13 of 105 in the MU Sofia syllabus for Biology (Medicine, Year 1). The free AceMed note covers it in 6 sections, about 417 words (3 min of reading), with 25 flashcards.
In this note
Prokaryotic genome and regulation of gene expression.
Gene Organization in Operons
Regulation of Gene Expression
RNA Polymerase and Sigma Factors
Mechanisms of Coordinated Gene Regulation
Transcription Termination in Prokaryotes
Prokaryotic genome and regulation of gene expression.
Bacterial DNA is typically a single circular, double-stranded DNA molecule.
The genome is compact with minimal noncoding DNA, mostly regulatory in nature.
The nucleoid is the region where the chromosome is located, distinct from the cytoplasm.
Chromosome is looped and compacted by Nucleoid-Associated Proteins (NAPs).
SMC complexes assist in chromosome structure and segregation during cell division.
E. coli genome has:
A single origin of replication (Ori).
A terminus (site where replication ends).
Genes spread throughout the chromosome (space-efficient).
Plasmids are extra-chromosomal circular DNA:
Can exist in one or thousands of copies.
Often carry survival genes (e.g., antibiotic resistance).
Transferred via conjugation using a pilus.
Some plasmids, called episomes, can integrate into the host chromosome.
Gene Organization in Operons
Genes in bacteria are often grouped in operons (not transcribed individually like in eukaryotes).
Operon components:
Structural genes – code for proteins.
Operator – DNA region controlling transcription.
Regulatory gene – codes for a protein that interacts with the operator.
Benefits:
Coordinated control of functionally related genes.
Efficient transcription and translation.
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