Bacterial DNA and Gene Expression

Study Notes

Bacterial DNA Structure

Bacterial genomes are typically circular, double-stranded DNA molecules.
They are located in the cytoplasm, not a nucleus.
The DNA is usually highly compacted and organized into a nucleoid region.
Plasmids are small, extrachromosomal, circular DNA molecules that can replicate independently.

Bacterial Gene Expression

Bacterial genes are organized into operons, which are groups of genes transcribed together.
This allows coordinated expression of genes involved in specific metabolic pathways.
Transcription occurs in the cytoplasm.
Translation of mRNA into protein also occurs in the cytoplasm, typically with multiple ribosomes working on the same mRNA molecule simultaneously.

Bacterial Genetic Exchange

Bacteria exchange genetic material through transformation, conjugation, and transduction.
Transformation: Uptake of free DNA from the environment.
Conjugation: Transfer of DNA from one bacterium to another through direct cell-to-cell contact, often involving a plasmid.
Transduction: Transfer of DNA from one bacterium to another by a bacteriophage (virus that infects bacteria).

Bacterial Mutation

Mutations are changes in the DNA sequence, spontaneous or induced by mutagens (physical or chemical agents).
Mutations can lead to changes in bacterial properties, such as drug resistance.
Some mutations are beneficial, some detrimental, and others neutral.
DNA proofreading and repair systems minimize mutation occurrence.

Genetic Engineering of Bacteria

Techniques like CRISPR-Cas9 are used to modify bacterial genomes for various purposes.
Techniques modify or eliminate specific genes.
This creates new strains capable of tasks like producing desired proteins or degrading pollutants.
Genetic engineering has significant applications in biotechnology and medicine.

Regulation of Bacterial Genes

Gene expression is tightly regulated in response to environmental changes.
Operons are controlled by regulatory proteins binding to specific DNA sequences, activating or repressing transcription.
These mechanisms allow bacteria to adapt to nutrient availability, antibiotic presence, and other factors.

Horizontal Gene Transfer

Horizontal gene transfer (HGT) is the transfer of genes between organisms, different from vertical inheritance.
HGT is vital for rapid bacterial evolution and adaptation.
HGT facilitates the acquisition of traits like antibiotic resistance, virulence factors, and specialized metabolic capabilities, driving bacterial diversity and new lineages.

Plasmids and their Role

Plasmids are extrachromosomal, self-replicating DNA molecules.
They are frequently used in molecular biology for cloning and gene expression.
Plasmids often carry genes conferring advantages, including antibiotic resistance, virulence factors, and other beneficial characteristics.
Conjugation transfers plasmids between bacteria, spreading beneficial genes.

Bacterial Resistance Mechanisms

Bacteria develop antibiotic resistance through mutations affecting antibiotic targets or acquisition of genes encoding antibiotic-degrading enzymes.
Horizontal gene transfer significantly spreads resistance genes, hindering antibiotic management.

Antibiotic Resistance Mechanisms—detail

Antibiotic resistance mechanisms include inactivation by enzymatic modification (e.g., β-lactamases inactivating β-lactams), alteration of target sites preventing drug binding, reduced antibiotic uptake due to changes in cell membrane permeability, and active antibiotic expulsion by efflux pumps.

Description

Explore the structure and function of bacterial DNA, including the organization of bacterial genomes and gene expression through operons. Understand the mechanisms of genetic exchange among bacteria, such as transformation and conjugation.