Microbial Metabolism, Genetics, Growth Control, and Pathogenesis Study Guide Unit 2

Microbial Metabolism

Metabolism, Anabolism, and Catabolism

Metabolism refers to all chemical reactions occurring within a cell, encompassing both energy-producing and energy-consuming processes.

• Anabolism: The synthesis of complex molecules from simpler ones; requires energy (endothermic).

• Catabolism: The breakdown of complex molecules into simpler ones; releases energy (exothermic).

• Endothermic Reaction: Absorbs energy from surroundings (e.g., photosynthesis).

• Exothermic Reaction: Releases energy (e.g., cellular respiration).

• Example: Glucose breakdown in glycolysis is catabolic and exothermic.

Enzymes and Coenzymes

Enzymes are biological catalysts that speed up metabolic reactions without being consumed.

• Characteristics: Specificity, efficiency, sensitivity to temperature and pH.

• Coenzymes: Organic molecules (often vitamins) that assist enzymes (e.g., NAD, FAD).

• Example: NAD acts as an electron carrier in cellular respiration.

Electron and Hydrogen Carriers

Electron carriers are molecules that transport electrons during metabolic reactions.

• NAD (Nicotinamide adenine dinucleotide): Accepts electrons and hydrogen.

• FAD (Flavin adenine dinucleotide): Accepts electrons and hydrogen.

• Coenzyme A: Transfers acetyl groups in metabolism.

Aerobic Respiration

Aerobic respiration is the process by which cells convert glucose and oxygen into energy, carbon dioxide, and water.

• General Balanced Equation:

$\mathrm{C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + ATP}$

• Final Hydrogen and Electron Acceptor: Oxygen (O2).

Glycolysis

Glycolysis is the first step in cellular respiration, breaking down glucose into pyruvate.

• Location: Cytoplasm of the cell.

• Activation Energy: 2 ATP molecules are invested to start glycolysis.

• Example: Glucose (6C) → 2 Pyruvate (3C each).

Krebs Cycle (Citric Acid Cycle)

The Krebs cycle further oxidizes pyruvate, generating electron carriers and ATP.

• ATP Yield: Each NADH2 yields 3 ATP; each FADH2 yields 2 ATP.

• Example: For each glucose, the cycle produces multiple NADH and FADH2.

Electron Transport System (ETS)

The ETS is the final stage of aerobic respiration, generating most ATP.

• Location in Bacteria: Cell membrane.

• ATP Generation: Most ATP is produced here via oxidative phosphorylation.

Fermentation and Anaerobic Respiration

Fermentation and anaerobic respiration occur in the absence of oxygen.

• Fermentation: Organic molecules are the final electron acceptors (e.g., pyruvate).

• Anaerobic Respiration: Inorganic molecules (e.g., nitrate, sulfate) are final electron acceptors.

• Difference: Fermentation does not use ETS; anaerobic respiration does.

Microbial Genetics

Genome, Genes, Genotype, and Phenotype

The genome is the complete set of genetic material in an organism.

• Gene: Segment of DNA coding for a protein or trait.

• Genotype: Genetic makeup of an organism.

• Phenotype: Observable traits resulting from genotype.

DNA Structure and Replication

DNA is a double helix with antiparallel strands; replication is semi-conservative.

• Antiparallel Arrangement: Strands run in opposite directions (5' to 3' and 3' to 5').

• Primer: RNA primer initiates replication; later removed by enzymes.

• Mutation: Change in DNA sequence.

RNA Structure and Function

RNA is single-stranded and comes in several forms, each with specific functions.

• mRNA: Messenger RNA; carries genetic code from DNA to ribosome.

• tRNA: Transfer RNA; brings amino acids to ribosome.

• rRNA: Ribosomal RNA; forms part of ribosome structure.

Transcription and Translation

Transcription is the synthesis of RNA from DNA; translation is the synthesis of protein from RNA.

• Transcription: DNA → RNA.

• Translation: RNA → Protein.

RNA Pairing and Codons

RNA pairs with DNA during transcription and with itself in secondary structures.

• RNA-DNA Pairing: A-U, T-A, C-G, G-C.

• Codon: Three-base sequence in mRNA coding for an amino acid.

• Anticodon: Three-base sequence in tRNA complementary to codon.

Horizontal Gene Transfer in Bacteria

Bacteria can exchange genetic material through several mechanisms.

• Transformation: Uptake of naked DNA from environment.

• Conjugation: Transfer of DNA via direct cell-to-cell contact (pilus).

• Genetic Engineering: Manipulation of genes for desired traits.

Microbial Growth Control

Definitions of Control Methods

Various terms describe methods to control microbial growth.

• Antisepsis: Removal of pathogens from living tissue.

• Degermation: Mechanical removal of microbes from skin.

• Disinfection: Removal of pathogens from inanimate objects.

• Sterilization: Complete destruction of all microbial life.

• Sanitation: Reduction of microbial population to safe levels.

Microbial Resistance

Microbes vary in their resistance to control methods.

• Easiest to Eliminate: Enveloped viruses, vegetative bacteria.

• Hardest to Eliminate: Bacterial endospores, prions.

Factors Influencing Antimicrobial Effectiveness

• Number of microbes

• Type of microbe

• Environment (organic matter, temperature, biofilms)

• Time of exposure

Physical Agents of Control

Physical methods are used to control microbial growth.

• Heat: Sterilization (autoclaving), pasteurization.

• Filtration: Removal of microbes from liquids or air.

• Radiation: UV, ionizing radiation for sterilization.

Chemical Agents of Control

Chemical methods are used for disinfection and antisepsis.

• Alcohols: Disinfect surfaces, skin.

• Halogens: Chlorine, iodine for water and surfaces.

• Phenolics: Disinfectants for surfaces.

• Quaternary Ammonium Compounds: Used in sanitation.

Pathogenesis and Epidemiology

The Microbiome

The microbiome is the collection of microorganisms living in and on the human body.

• Origin: Acquired at birth and from environment.

Colonization, Infection, and Disease

Microbes interact with hosts in various ways.

• Colonization: Establishment of microbes without causing disease.

• Infection: Invasion and multiplication of microbes in host.

• Disease: Disruption of normal host function due to infection.

Steps in Causing Disease

Pathogenesis involves several steps.

• Entry into host

• Attachment to host tissues

• Survival and multiplication

• Causing damage (toxins, immune response)

• Exotoxin: Secreted proteins causing damage (e.g., tetanus toxin).

• Endotoxin: Lipid A component of Gram-negative bacteria released upon cell death.

Signs vs. Symptoms

• Sign: Objective evidence of disease (e.g., fever).

• Symptom: Subjective experience (e.g., pain).

Patterns of Transmission

Communicable diseases can be transmitted in various ways.

• Direct contact

• Indirect contact (fomites)

• Vehicle transmission (water, food)

• Vector transmission (insects)

Koch’s Postulates

Koch’s Postulates are criteria to establish a microbe as the cause of a disease.

• Microbe must be found in all cases of disease.

• Microbe must be isolated and grown in pure culture.

• Pure culture must cause disease in healthy host.

• Microbe must be re-isolated from experimentally infected host.

Morbidity vs. Mortality

• Morbidity: Incidence of disease.

• Mortality: Incidence of death.

Key Epidemiological Terms

Term	Definition
Reservoir	Source of pathogen (e.g., humans, animals, environment)
Nosocomial	Hospital-acquired infection
Fomite	Inanimate object transmitting disease
Vehicle	Non-living carrier (e.g., water, food)
Vector	Living carrier (e.g., mosquito)
Communicable	Transmissible from person to person
Contagious	Highly transmissible