Microbiology Exam II Study Guide: Key Concepts and Applications

Microbial Metabolism and Bioenergetics

Respiratory Chains in Bacteria vs. Mitochondria

Respiratory chains are essential for ATP production in both bacteria and mitochondria, but their structure and function can differ.

• ATP Yield: The magnitude of proton motive force (PMF) and ATP yield can vary under different conditions, helping distinguish between bacterial and mitochondrial chains.

• Electron Acceptors: Bacteria may use a variety of terminal electron acceptors, while mitochondria primarily use oxygen.

• Inhibitor Sensitivity: Sensitivity to specific inhibitors can help identify the type of respiratory chain.

Example: Cyanide inhibits cytochrome c oxidase in mitochondria but may not affect all bacterial chains.

Methanogenesis in Archaea

Methanogenic Archaea produce methane as a metabolic byproduct under anaerobic conditions.

• Key Reaction: Reduction of CO2 using electrons from hydrogen gas (H2).

• Ecological Role: Important in anaerobic environments such as wetlands and the guts of ruminants.

Equation: $CO_2 + 4H_2 \rightarrow CH_4 + 2H_2O$

Microbial Genetics and Molecular Biology

Central Dogma of Biology

The central dogma describes the flow of genetic information in cells.

• Modern View: DNA → RNA → Protein, with additional roles for reverse transcription and non-coding RNAs.

• Exceptions: Some viruses use RNA as genetic material and reverse transcription (RNA → DNA).

DNA Replication and PCR

DNA replication is semi-conservative and involves several key enzymes.

• Steps in PCR:

  1. Denature the DNA (separate strands)

  2. Anneal primers

  3. Extend new DNA strands with DNA polymerase

• Enzymes: DNA polymerase adds nucleotides to the 3' end of a growing DNA strand.

Transcription and Translation

Transcription produces RNA from a DNA template; translation synthesizes proteins from mRNA.

• Shine-Dalgarno Sequence: In bacteria, this ribosomal binding site helps initiate translation.

• tRNA: Transfers specific amino acids to the ribosome during protein synthesis.

• Wobble Hypothesis: Some tRNAs recognize multiple codons due to flexible base pairing at the third codon position.

Genetic Engineering and Cloning

Recombinant DNA technology allows for the manipulation and cloning of genes.

• Restriction Enzymes: Cut DNA at specific sequences, often palindromic.

• Vectors: Plasmids are commonly used to clone and propagate foreign DNA in bacteria.

• Electrophoresis: Separates DNA fragments by size for analysis.

Microbial Growth and Control

Microbial Growth Phases

Bacterial growth in batch culture follows distinct phases: lag, log, stationary, and death.

• Lag Phase: Cells adapt to new environment; little division.

• Log Phase: Exponential growth and division.

• Stationary Phase: Nutrient depletion slows growth; cell death balances division.

• Death Phase: Cells die at an exponential rate.

Control of Microbial Growth

Various physical and chemical methods are used to control microbial growth.

• Disinfectants: Chemicals like phenol, glutaraldehyde, and QUATs are used for surface and instrument sterilization.

• Antimicrobial Agents: Selection depends on the type of microorganism and application.

Instrument	Antimicrobial Method
Examination table	Phenolic (e.g., Lysol)
Oral thermometer	Alcohol wipe
Fiberoptic endoscope	Glutaraldehyde
Clinical (shared) stethoscope	Hydrogen peroxide
Hospital laundry	QUAT

Viruses, Viroids, and Prions

Viral Life Cycles

Viruses can cause acute, latent, or chronic infections.

• Chronic Viruses: Persistently infect host cells, often with ongoing viral production and mild or no symptoms.

• Latent Viruses: Remain dormant in host cells and can reactivate later.

Viral Structure

Viruses consist of genetic material (DNA or RNA), a protein coat (capsid), and sometimes an envelope.

• Enveloped Viruses: Surrounded by a lipid membrane derived from the host cell.

• Icosahedral Symmetry: Many viruses have a symmetrical, 20-sided capsid.

Principles of Disease and Epidemiology

Pathogenic Mechanisms

Microorganisms cause disease through various mechanisms, including toxin production and immune evasion.

• Parasitic Infections: Some algae produce toxins that cause shellfish poisoning in humans.

• Schistosomiasis: A parasitic disease involving a complex life cycle with snails as intermediate hosts.

Antimicrobial Drugs

Antimicrobial agents target specific microbial processes.

• Competitive Inhibitors: Drugs like sulfonamides inhibit folic acid synthesis in bacteria.

• Antibiotic Selection: Choice depends on the pathogen and resistance patterns.

Immunity and Host Defenses

Innate and Adaptive Immunity

The immune system protects against pathogens through innate and adaptive mechanisms.

• Polymorphonuclear Cells (PMNs): Include neutrophils, which are phagocytic and play a key role in innate immunity.

• Inflammatory Response: Characterized by vasodilation, increased permeability, and recruitment of immune cells.

Complement System

The complement system enhances immune responses through a cascade of protein activations.

• Functions: Opsonization, lysis of pathogens, and promotion of inflammation.

• Activation Pathways: Classical, alternative, and lectin pathways.

Biotechnology and DNA Technology

Gene Cloning and Libraries

Gene cloning involves inserting DNA fragments into vectors to create libraries for research or biotechnology.

• Steps: Isolate DNA, cut with restriction enzymes, ligate into vectors, transform into host cells, and screen for desired clones.

• Screening: May involve antibiotic resistance or colorimetric markers.

Applications of Biotechnology

Biotechnology enables the production of pharmaceuticals, genetically modified organisms, and gene therapy.

• Gene Therapy: Involves moving a gene from a silent site to an expressed site to restore function.

• Probes: Used to detect specific DNA sequences in research and diagnostics.