Microbiology: DNA and Mutation Quiz

Microbial Genetics Overview

• Microbial genetics is the study of heritable information in microorganisms, including bacteria, archaea, viruses, and some protozoa and fungi.

Objectives

• Review the nature of genetic elements of bacteria
• Understand the mechanisms of genetic changes in microorganisms
• Understand the microbiological and clinical significance of microbial genetic variations and their application

Bacterial Genetic Elements

• Chromosome: Typically circular, double-stranded DNA molecules carrying essential genetic information for bacterial survival and function. Includes genes for metabolism, growth, and reproduction.
• Plasmids: Small, circular, extrachromosomal DNA molecules. Generally not essential for survival but often confer antibiotic resistance. Smaller than bacterial chromosomes, and can replicate independently. Plasmid size ranges from 1 to 250 kbps, and copy number per cell can vary from 1-100 copies. Plasmids occur in bacteria and some eukaryotes (like yeasts).

Mutation

• Mutations are alterations (changes) in a cell's DNA nucleotide sequence.
• Most mutations lead to harmful changes, but some can be beneficial.
• Mutations are a major source of biological diversity.

Types of Mutations by Origin

• Spontaneous mutations: Naturally occurring mutations during replication caused by errors during the process. Not caused by external agents.
• Induced mutations: Occur when external agents (mutagens) chemically alter DNA, usually causing DNA damage. Mutagens include both physical and chemical factors that increase mutation rates. Mutagens can be grouped into radiation and chemical mutagens.

Types of Mutations by Size

• Gross mutations: Large changes involving portions or entire genes.
• Point mutations: Small changes affecting a single nucleotide.
  • Substitution mutations: One nucleotide is substituted for another (includes missense, nonsense, and silent mutations). Missense mutations change the codon and amino acid. Same-sense (silent) mutations alter the codon but do not affect the amino acid. Nonsense mutations change a codon into a stop codon.
  • Frame-shift mutations: Insertions or deletions of nucleotides that change the reading frame, altering downstream amino acid sequence. Frame-shift mutations may lead to premature stop codons (nonsense mutations) and non-functional proteins.

Recombination (Gene Transfer)

• Recombination: Exchange or acquisition of genetic material between different DNA molecules. Results in acquisition of new traits like antibiotic resistance.
• Types of Recombination:
  • Transformation: Uptake of free DNA fragments from dead or degraded bacteria, exchanging for a piece of recipient cell's DNA. A crucial step where bacterial cells acquire new pieces of DNA.
  • Transduction: Transfer of bacterial DNA by bacteriophages (viruses that infect bacteria). Bacteriophages infect a cell, replicate, and transfer bacterial DNA to other cells through viral pathways.
  • Conjugation: Direct cell-to-cell contact. Donor cells have F-pilus (F+). Donor cells transfer their DNA to recipient cells (F-).

Microbiological and Clinical Significance

• Antibiotic Resistance: Acquisition of resistance genes (via plasmids or mutations) is a significant challenge. Understanding resistance mechanisms helps develop strategies to combat resistance.
• Virulence Factors: Genetic variations in pathogens can influence associated infection severity. Studying these variations aids in targeted therapies.
• Biotechnology: Exploits biological systems to create products, like commercial protein production (e.g., insulin) and pharmaceutical manufacturing. Techniques involving gene modification and gene therapy applications.
• Viral Vectors: Viruses genetically modified to deliver or express other genes are used in various applications, including vaccinations and gene therapy. Viral vectors are used for gene therapies, as well as to treat inherited diseases.
• Gene Therapy: Transfer of genetic material into cells to treat diseases, typically inherited diseases. Includes viral and non-viral approaches.