Microbiology Exam II: Comprehensive Study Notes

Microbial Metabolism and Bioenergetics

Proton Motive Force (PMF) and Respiratory Chains

The proton motive force (PMF) is a key concept in microbial metabolism, representing the electrochemical gradient generated across a membrane during electron transport. It drives ATP synthesis and other cellular processes.

• Magnitude of PMF: Can vary depending on the electron donor and acceptor used in the respiratory chain.

• Testing PMF: Measuring ATP production under different conditions can help determine the PMF's magnitude.

• Example: Bacteria using oxygen as an electron acceptor typically generate a higher PMF than those using nitrate.

Methanogenesis and Archaeal Metabolism

Methanogenic Archaea are unique microorganisms that produce methane as a metabolic byproduct, often using CO2 as an electron acceptor and H2 as an electron donor.

• Key Reaction: CO2 reduced to CH4 using electrons from H2.

• Significance: Important in anaerobic environments such as wetlands and the digestive tracts of ruminants.

Microbial Genetics and Molecular Biology

Central Dogma of Biology

The Central Dogma describes the flow of genetic information: DNA → RNA → Protein. Modern updates include additional processes such as reverse transcription and RNA replication.

• Key Processes: Replication, Transcription, Translation.

• Exceptions: Some viruses use RNA as genetic material and can reverse transcribe RNA to DNA.

• Example: Retroviruses (e.g., HIV) use reverse transcriptase to convert RNA to DNA.

DNA Replication and PCR

Polymerase Chain Reaction (PCR) is a technique used to amplify DNA sequences.

• Steps:

  1. Denature DNA (separate strands)

  2. Anneal primers (bind to target sequence)

  3. Extend DNA (DNA polymerase synthesizes new strand)

• Enzymes: DNA polymerase is essential for the extension step.

Transcription and Translation

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

• Promoter: DNA sequence where RNA polymerase binds to initiate transcription.

• Codons: Triplets of nucleotides in mRNA that specify amino acids.

• tRNA: Transfer RNA molecules recognize codons via their anticodon and deliver the correct amino acid.

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

Microbial Growth and Control

Microbial Growth

Microbial growth refers to the increase in cell number, typically via binary fission.

• Growth Curve: Includes lag, log, stationary, and death phases.

• Factors Affecting Growth: Nutrient availability, temperature, pH, and oxygen levels.

Control of Microbial Growth

Various methods are used to control microbial growth, especially in medical settings.

• Disinfection: Reduces or eliminates pathogens on surfaces.

• Antimicrobial Agents: Chemicals such as phenol, glutaraldehyde, and quaternary ammonium compounds (QUATs) are used for disinfection.

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

• Example Table:

Instrument	Antimicrobial Method
Examination table	Phenolic (e.g., Lysol)
Criminal (surgical) knife	Glutaraldehyde
Thermal (burn) endoscope	Hydrogen peroxide
Surgical sponge	Quaternary ammonium salt (QUAT)

Viruses, Viroids, and Prions

Viral Life Cycles

Viruses can have acute or chronic infections. Chronic viruses persist in the host for long periods, sometimes without symptoms.

• Acute Infection: Rapid onset, short duration.

• Chronic Infection: Long-term persistence, may be asymptomatic.

Virus Structure

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

• Capsid: Protein shell protecting viral genome.

• Envelope: Lipid membrane derived from host cell.

• Example: Influenza virus has an envelope and surface glycoproteins.

Microbial Mechanisms of Pathogenicity and Disease

Pathogenicity and Virulence Factors

Pathogens possess various mechanisms to cause disease, including toxins, enzymes, and evasion of host defenses.

• Virulence Factors: Traits that enhance a microbe's ability to cause disease (e.g., capsule, toxins).

• Example: Streptococcus pneumoniae uses a capsule to evade phagocytosis.

Parasitic and Fungal Infections

Parasitic life cycles often involve multiple hosts and complex developmental stages.

• Schistosomiasis: Eggs are released in human feces, hatch in water, and infect snails as intermediate hosts.

• Fungal Infections: Treated with antifungal agents such as fluconazole.

Immunology: Innate and Adaptive Immunity

Innate Immunity

Innate immunity provides immediate, nonspecific defense against pathogens.

• Physical Barriers: Skin, mucous membranes.

• Cellular Defenses: Phagocytes (neutrophils, macrophages), natural killer cells.

• Complement System: A group of proteins that enhance phagocytosis, lyse pathogens, and promote inflammation.

Adaptive Immunity

Adaptive immunity is specific and involves memory. It includes humoral (antibody-mediated) and cellular responses.

• B cells: Produce antibodies.

• T cells: Help regulate immune responses and kill infected cells.

Biotechnology and DNA Technology

Cloning and Gene Libraries

Gene cloning involves creating a library of DNA fragments and identifying specific genes of interest.

• Steps:

  1. Clones are transferred to filter paper.

  2. Colonies are lysed and DNA is denatured.

  3. DNA is hybridized with a labeled probe.

  4. Electrophoresis separates DNA fragments.

Restriction Enzymes and DNA Manipulation

Restriction enzymes cut DNA at specific sequences, often producing palindromic sites.

• Palindromes: Sequences that read the same forward and backward (e.g., 5'-GAATTC-3').

• Applications: Used in cloning, gene mapping, and genetic engineering.

Antimicrobial Drugs

Antibiotics and Antifungals

Antimicrobial drugs are used to treat bacterial, fungal, and parasitic infections.

• Antibiotics: Penicillin, ciprofloxacin, and others target bacterial cell wall synthesis, DNA replication, or protein synthesis.

• Antifungals: Fluconazole is used to treat fungal infections such as tinea corporis.

Additional info:

• Some explanations and examples were expanded for clarity and completeness.

• Tables and stepwise lists were inferred from context and standard microbiology knowledge.