Microbiology for Allied Health Professions

Definition of Genetics: The study of inheritance, or heredity of living things.
- Etymology: From Greek term γενετικός (genetikos), meaning origins.
- Key aspects:
- Transmission of biological properties (traits) from parent to offspring.
- Expression and variation of traits.
- Regulation of genes.
- Structure and function of genetic material.
- Changes in genetic material.

Genotype: The sum of all gene types; the distinctive genetic makeup of an organism.
Phenotype: The expression of certain traits (structures or functions).
- Important Note: Organisms contain more genes in their genotypes than are manifested in the phenotype at any given time.

Definition: Chromosomes contain the genetic material necessary for reproducing an organism.
- Structure: Compacted complexes of DNA and proteins (e.g., histones in eukaryotes, IHF in prokaryotes).
Genome: Refers to all genetic material that an organism possesses:
- Bacteria: Typically have a single haploid circular chromosome.
- Eukaryotes: A complete set of nuclear chromosomes; include mitochondrial genome in animals and chloroplast genome in plants.
- Plasmids: Found in bacteria, can carry additional genes.
- Viruses: Viral genomes can contain either DNA or RNA.

Nucleoid: The region where bacterial chromosome is found; not membrane-bound.
- Contact: DNA is in direct contact with the cytoplasm.
- Transcription and Translation: Coupled processes in bacteria.
Examples of Bacteria with Multiple Chromosomes:
- Rhodobacter sphaeroides, Vibrio cholerae, Agrobacterium tumefaciens, Burkholderia cepacia.
Linear Chromosomes: Found in Borrelia burgdorferi, Streptomyces spp.

Bacterial chromosomes are usually circular molecules a few million nucleotides in length:
- Escherichia coli: ~4.6 million base pairs.
- Haemophilus influenzae: ~1.8 million base pairs.
- Mycoplasma genitalium: ~580,000 base pairs.
- Typical structure: Contains a few thousand different genes; structural gene sequences (encoding proteins) comprise the majority of bacterial DNA.

Size Variability: Ranges from a few thousand to more than one hundred thousand nucleotides.
- Largest Virus: Megavirus chilensis; Genome: ~1,300,000 bp.
- Smallest Virus: Porcine circovirus; Genome: ~1,800 bp.
Organization: Can be circular, linear, or segmented (collection of segments).

Components:
- Phosphate group, D-Deoxyribose (in DNA), Nitrogenous bases: Purines (Adenine [A], Guanine [G]), and Pyrimidines (Thymine [T], Cytosine [C]).
Base Pairing:
- Purines and pyrimidines join through hydrogen bonds; specific base pairing rules:
- Adenine (A) pairs with Thymine (T).
- Guanine (G) pairs with Cytosine (C).
- Chargaff's Rule: Base pairing governed by hydrogen bond formation; DNA easily unzips due to weak hydrogen bonds between bases.

Semi-conservative Replication: Each new double helix consists of one original and one new strand.
Origin of Replication: AT-rich regions make it easier to separate strands for replication.
Key Enzymes in Replication:
- Topoisomerases: Unwind DNA helix.
- Helicases: Unzip double-stranded DNA.
- Primase: Synthesizes RNA primer to start DNA synthesis.
- DNA Polymerase III: Adds nucleotides in a 5’ to 3’ direction.
- DNA Ligase: Joins Okazaki fragments on lagging strand.
Leading vs Lagging Strand:
- Leading strand synthesized continuously.
- Lagging strand synthesized in fragments (Okazaki fragments).

DNA Polymerase III: Identifies and removes mismatched nucleotides using 3’ to 5’ exonuclease activity.

Describes the flow of genetic information:
- From DNA to RNA (Transcription).
- From RNA to Protein (Translation).
Regulatory RNAs: Micro RNAs, Antisense RNAs, Riboswitches.

Codon Recognition: Codons encode amino acids; tRNA carries corresponding anticodons.
- Start Codon: Typically AUG (Methionine).
- Stop Codons: UAA, UAG, UGA; no corresponding tRNAs.
Polyribosomal Complex: Allows multiple ribosomes to translate the same mRNA strand.
- Post-Translational Modifications: Modifications post-synthesis to stabilize and finalize proteins.

Operons: Genetic regulatory systems typically found in bacteria.
Lac Operon: Regulates lactose metabolism in E. coli.
- Components: Regulatory gene, control locus (promoter and operator), structural locus.
Types of Regulation:
- Inducible (turned on by substrate presence).
- Repressible (turned off by product presence).

Definition: Transfer of genetic material between organisms that did not come from parental organisms.
Types:
- Conjugation: Direct contact and DNA transfer between bacteria.
- Transformation: Uptake of naked DNA from the environment.
- Transduction: Transfer of DNA via bacteriophage.

Definition: Accidental or unplanned change in a nucleotide sequence.
- Types of Mutations:
- Point Mutations: Affecting a single base; include missense, nonsense, and silent mutations.
- Frameshift Mutations: Changes reading frame due to insertions or deletions.
- Repair Mechanisms: Cells have proofreading and DNA repair systems to correct errors.

Potential Effects: Beneficial, neutral, or harmful mutations can occur. Lethal mutations cause dysfunction or death of the cell.

Understanding genetics, mutations, and gene regulation is vital in microbiology, especially considering phenomena like antibiotic resistance and pathogen virulence.