BIO 246 Exam 2 Study Guide: Genetics, Growth Control, Bacterial Classification, and Fungi

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: $\text{DNA} \xrightarrow{\text{Replication}} \text{DNA} + \text{DNA}$

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: $\text{DNA} \xrightarrow{\text{Transcription}} \text{mRNA} \xrightarrow{\text{Translation}} \text{Protein}$

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: $\text{Microbes} + \text{Sterilization} \rightarrow \text{No viable microbes}$

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.

Bacterial Group	Examples	Key Features
Gram + cocci	Staphylococci, Streptococci	Thick peptidoglycan wall, purple stain
Gram - cocci	Neisseria	Thin wall, outer membrane, pink stain
Gram + rods	Bacillus, Clostridium	Endospore forming, aerobic/anaerobic
Gram - rods	Pseudomonas, Bordetella, Salmonella	Various diseases, motility, pigment production
Gram - spirals	Vibrio	Spiral shape, motility
Mycoplasmas	Mycoplasma pneumoniae	No cell wall, sterols in 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.