Core Principles of Microbiology: Chemical Foundations, Cell Structure, Metabolism, Growth, Control, and Genetics

Ch. 2 – Chemical Principles in Microbiology

Properties of Water

Water is essential for all living organisms and plays a critical role in microbial physiology and chemistry.

• Polarity: Water molecules are polar, allowing them to form hydrogen bonds and dissolve many substances.

• Cohesion and Adhesion: Hydrogen bonding leads to high surface tension and capillary action.

• Solvent Properties: Water dissolves ionic and polar compounds, facilitating biochemical reactions.

• Thermal Stability: High specific heat helps maintain stable temperatures in cells.

Chemical Bonds

• Ionic Bonds: Formed by the transfer of electrons between atoms (e.g., NaCl).

• Covalent Bonds: Atoms share electrons (e.g., H2O, organic molecules).

• Hydrogen Bonds: Weak bonds between a hydrogen atom and an electronegative atom (e.g., between water molecules).

Hydrolysis and Dehydration Synthesis

• Hydrolysis: Breaking down complex molecules by adding water.

• Dehydration Synthesis: Joining two molecules by removing water.

• Example: Formation and breakdown of polysaccharides, proteins, and nucleic acids.

Properties of Carbon Chains

Carbon forms the backbone of organic molecules, allowing for diversity in structure and function.

• Variety: Chains can be straight, branched, or ring-shaped.

• Functional Groups: Attachments such as hydroxyl, carboxyl, amino, and phosphate groups determine chemical properties.

Macromolecules

Macromolecules are large, complex molecules essential for life. They include lipids, carbohydrates, proteins, and nucleic acids.

Type	Components	Structure	Function	Examples
Carbohydrates	Monosaccharides	Ring or linear	Energy storage, structure	Glucose, cellulose
Lipids	Glycerol, fatty acids	Hydrophobic tails	Membranes, energy storage	Phospholipids, triglycerides
Proteins	Amino acids	Polypeptide chains	Catalysis, structure, transport	Enzymes, antibodies
Nucleic Acids	Nucleotides	Double/single helix	Genetic information	DNA, RNA

Ch. 3 – Observing Microorganisms Through a Microscope

Staining Procedures

• Simple Stain: Uses a single dye to highlight cells; reveals shape and arrangement.

• Gram Stain: Differentiates bacteria into Gram-positive (purple) and Gram-negative (pink) based on cell wall structure.

• Steps of Gram Stain:

  1. Crystal violet (primary stain)

  2. Iodine (mordant)

  3. Alcohol (decolorizer)

  4. Safranin (counterstain)

• Purpose: Identifies bacterial type for diagnosis and treatment.

Types of Microscopes

• Compound Light Microscope: General observation of stained specimens.

• Phase-Contrast Microscope: Observes live, unstained cells; enhances contrast.

• Darkfield Microscope: Visualizes thin or transparent organisms; background appears dark.

• Fluorescence Microscope: Detects fluorescently labeled structures or organisms.

• Electron Microscope: High-resolution imaging of ultrastructure (TEM and SEM).

Ch. 4 – Functional Anatomy of Prokaryotic and Eukaryotic Cells

Cell Shapes

• Coccus: Spherical

• Bacillus: Rod-shaped

• Spirillum: Spiral

• Vibrio: Comma-shaped

• Spirochete: Flexible spiral

Plasma Membrane: Structure and Function

• Structure: Phospholipid bilayer with embedded proteins.

• Function: Selective barrier, transport, energy generation, cell signaling.

Transport Across Plasma Membrane

• Isotonic Solution: No net water movement; cell remains unchanged.

• Hypertonic Solution: Water leaves cell; cell shrinks (plasmolysis).

• Hypotonic Solution: Water enters cell; cell may burst (lysis).

Cell Wall Structures

• Gram-Positive: Thick peptidoglycan layer, teichoic acids, stains purple.

• Gram-Negative: Thin peptidoglycan, outer membrane with lipopolysaccharide (LPS), stains pink.

Specialized Structures

• Capsule: Polysaccharide layer; protects against phagocytosis.

• Endospores: Resistant, dormant structures for survival in harsh conditions.

• Slime Layer: Loosely attached glycocalyx; aids in adherence.

Diffusion

• Passive Diffusion: Movement down concentration gradient without energy.

• Active Transport: Movement against gradient using energy (ATP).

Endosymbiotic Theory

• Concept: Eukaryotic organelles (mitochondria, chloroplasts) originated from prokaryotic cells engulfed by ancestors of eukaryotes.

• Evidence: Double membranes, own DNA, ribosomes similar to bacteria.

Ch. 5 & 6 – Microbial Metabolism and Growth

Microbial Nutrition Types

Type	Energy Source	Carbon Source	Example
Chemoautotroph	Chemicals	CO2	Nitrosomonas
Chemoheterotroph	Chemicals	Organic compounds	Most bacteria, animals
Photoautotroph	Light	CO2	Cyanobacteria
Photoheterotroph	Light	Organic compounds	Rhodobacter

Microbial Growth Conditions

• Mesophiles: Moderate temperature (20–45°C).

• Psychrophiles: Cold-loving (<20°C).

• Thermophiles: Heat-loving (>45°C).

• Halophiles: Salt-loving.

• Capnophiles: Require high CO2 levels.

• Anaerobes: Grow without oxygen.

• Facultative Anaerobes: Grow with or without oxygen.

• Aerobes: Require oxygen.

• Aerotolerant Anaerobes: Tolerate oxygen but do not use it.

• Microaerophiles: Require low oxygen levels.

Glycolysis

• Definition: Breakdown of glucose to pyruvate, producing ATP and NADH.

• Equation:

$\mathrm{Glucose} + 2\ \mathrm{NAD}^+ + 2\ \mathrm{ADP} + 2\ \mathrm{P_i} \rightarrow 2\ \mathrm{Pyruvate} + 2\ \mathrm{NADH} + 2\ \mathrm{ATP} + 2\ \mathrm{H_2O}$

Enzyme Function and Regulation

• Active Site: Region where substrate binds and reaction occurs.

• Factors Affecting Enzyme Activity: Temperature, pH, substrate concentration.

• Inhibition:

  • Competitive: Inhibitor binds active site.

  • Non-competitive: Inhibitor binds elsewhere, changing enzyme shape.

Electron Transport Chain (ETC)

• Function: Series of proteins transfer electrons, generating ATP via oxidative phosphorylation.

Ch. 7 – Control of Microbial Growth

Physical Methods

• Autoclave: Uses steam under pressure to sterilize (kills endospores).

• Gamma Radiation: Damages DNA, sterilizes medical equipment.

• Microwaves: Heat kills microbes, but uneven heating can leave survivors.

• Sunlight: Contains UV, can damage DNA but less effective than artificial UV.

• Ultraviolet Radiation: Causes thymine dimers in DNA, inhibiting replication.

Chemical Agents

Agent	Mechanism	Example/Application
Chlorine	Oxidizes cellular components	Water disinfection
Glutaraldehyde	Cross-links proteins	Equipment sterilization
Hydrogen Peroxide	Oxidizing agent	Surface antiseptic
Iodine	Disrupts proteins and membranes	Skin antiseptic
Ozone	Oxidizes cell components	Water treatment

• General Mechanisms: Disrupt plasma membranes, denature proteins, oxidize cellular components.

Definitions

• Disinfectant: Chemical used on inanimate objects to kill microbes.

• Antiseptic: Chemical used on living tissue to reduce infection risk.

• Aseptic: Free from contamination by pathogens.

• Fungicide: Kills fungi.

• Virucide: Inactivates viruses.

Ch. 8 – Microbial Genetics

Genetic Processes

• Replication: DNA is copied by DNA polymerase.

• Transcription: DNA is transcribed to mRNA by RNA polymerase.

• Translation: mRNA is translated into protein by ribosomes (with tRNA and rRNA).

• Transformation: Uptake of naked DNA from the environment.

• Replica Plating: Technique to isolate mutants by transferring colonies to new media.

Enzymes in Genetic Processes

Process	Enzyme	Function
Replication	DNA polymerase	Synthesizes new DNA strand
Transcription	RNA polymerase	Synthesizes RNA from DNA template
Translation	Ribosome (rRNA + proteins)	Assembles amino acids into proteins

Gene Regulation: Operon Model

• Operon: Cluster of genes under control of a single promoter.

• Inducible Genes: Turned on in response to a substrate (e.g., lac operon).

• Repressible Genes: Turned off when end product is abundant (e.g., trp operon).

• Micro RNAs: Small RNAs that regulate gene expression post-transcriptionally.

Mutations

• Substitution: One base is replaced by another; may be silent, missense, or nonsense.

• Frameshift: Insertion or deletion shifts reading frame, altering downstream amino acids.

Effects of Radiation on DNA

• Ionizing Radiation: Breaks DNA strands, causing mutations.

• UV Radiation: Causes thymine dimers, leading to replication errors.

Griffith's Experiments and Transformation

• Griffith's Experiment: Demonstrated transformation in Streptococcus pneumoniae—non-virulent bacteria became virulent when mixed with heat-killed virulent cells.

• Transformation: Uptake and incorporation of foreign DNA by a cell.

Additional info: The above notes expand on brief points with academic context, definitions, and examples for clarity and completeness.