Genetics

Genotypes and Phenotypes

Genotype refers to the genetic makeup of an organism, while phenotype is the observable physical or biochemical characteristics determined by both genotype and environment.

• Genotype: The set of genes carried by an organism.

• Phenotype: The expression of those genes as traits.

• Example: Bacteria with a gene for antibiotic resistance (genotype) will survive in the presence of the antibiotic (phenotype).

DNA Replication

DNA replication is the process by which a cell duplicates its DNA before cell division, ensuring genetic continuity.

• Enzymes involved: DNA polymerase, helicase, primase, ligase.

• Steps: Unwinding of DNA, synthesis of new strands, proofreading and repair.

• Leading vs. Lagging Strand: Leading strand is synthesized continuously; lagging strand is synthesized in Okazaki fragments.

• Equation:

Transcription and Translation

Transcription is the synthesis of RNA from DNA, while translation is the synthesis of proteins from mRNA.

• Transcription: Occurs in the cytoplasm of prokaryotes and nucleus of eukaryotes. Uses RNA polymerase.

• Translation: Occurs in ribosomes. Involves mRNA, tRNA, and rRNA.

• Components needed: Ribosomes, mRNA, tRNA, amino acids.

• Equation:

Mutations

Mutations are changes in the DNA sequence that can affect gene function and phenotype.

• Types: Point mutations, frame shift mutations, silent mutations.

• Causes: Errors in replication, environmental factors (e.g., radiation, chemicals).

• Example: Sickle cell anemia is caused by a point mutation in the hemoglobin gene.

Gene Transfer in Bacteria

Bacteria can exchange genetic material through transformation, transduction, and conjugation.

• Transformation: Uptake of naked DNA from the environment.

• Transduction: Transfer of DNA via bacteriophages.

• Conjugation: Direct transfer of DNA between bacteria via pilus.

• F+, F-, and F' cells: F+ cells have fertility plasmid; F- cells do not; F' cells have plasmid with some chromosomal genes.

• Generalized vs. Specialized Transduction: Generalized can transfer any gene; specialized transfers specific genes.

Growth Control

Sterilization, Disinfection, and Antisepsis

These are methods used to control microbial growth and prevent infection.

• Sterilization: Complete destruction of all forms of microbial life, including spores.

• Disinfection: Elimination of most pathogenic microorganisms (not spores) on inanimate objects.

• Antisepsis: Destruction of microorganisms on living tissue.

• Bacteriostatic vs. Bactericidal: Bacteriostatic inhibits growth; bactericidal kills bacteria.

• Physical methods: Heat (autoclaving, boiling), radiation, filtration.

• Chemical agents: Alcohols, chlorine, iodine, ethylene oxide.

• Equation:

Disinfectants and Antiseptics

• Disinfectants: Used on non-living surfaces (e.g., bleach, phenolics).

• Antiseptics: Used on living tissue (e.g., iodine, alcohol).

• Mode of action: Disrupt cell membranes, denature proteins, oxidize cellular components.

Bacterial Classification

Gram Staining and Morphology

Bacteria are classified by Gram stain reaction and shape.

• Gram-positive cocci: Staphylococci, Streptococci

• Gram-negative cocci: Neisseria

• Gram-positive rods: Bacillus (endospore forming), Clostridium

• Gram-negative rods: Pseudomonas aeruginosa, Bordetella pertussis, Salmonella, Shigella, Escherichia coli

• Gram-negative spirals: Vibrio

• Mycoplasmas: Only bacteria without cell wall; have sterols in plasma membrane.

Fungi

Fungi vs. Bacteria

Fungi are eukaryotic organisms distinct from bacteria, which are prokaryotic.

• Fungi: Eukaryotic, have nuclei and organelles, cell wall made of chitin.

• Bacteria: Prokaryotic, no nucleus, cell wall made of peptidoglycan.

• Fungal characteristics: Multicellular (molds) or unicellular (yeasts), reproduce by spores.

Hyphae and Mycelia

Hyphae are the thread-like structures of fungi; mycelium is a mass of hyphae.

• Septate hyphae: Have cross-walls (septa).

• Coenocytic hyphae: No septa; multinucleate.

• Vegetative mycelium: Grows into substrate for nutrient absorption.

• Aerial mycelium: Grows above surface, produces spores.

Fungal Infections

Fungi can cause a variety of infections, some of which are contagious.

• Yeast infections: Candida albicans causes vaginal yeast infections.

• Ringworm: Dermatophytes cause cutaneous infections.

• Transmission: Direct contact, fomites, airborne spores.

• Contagiousness: Most fungal infections are not highly contagious; exceptions exist.

Fungal Cell Structure

• Cell wall: Composed of chitin.

• Plasma membrane: Contains ergosterol.

• Reproduction: Sexual and asexual spores.

Classification of Fungi

• Yeasts: Unicellular fungi.

• Molds: Multicellular, filamentous fungi.

• Dimorphic fungi: Can exist as yeast or mold depending on environment.

Examples of Fungi

• Candida albicans: Causes yeast infections.

• Dermatophytes: Cause ringworm and athlete's foot.

Additional info: Academic context and definitions have been expanded for clarity and completeness.