Microbiology Study Notes: Chemical Principles, Microscopy, Cell Structure, Metabolism, Microbial Growth, Control of Microbial Growth, and Microbial Genetics

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Ch. 2 – Chemical Principles in Microbiology

Properties of Water

Water is essential for all living organisms and plays a critical role in microbial life due to its unique chemical properties.

Polarity: Water molecules are polar, allowing them to form hydrogen bonds and dissolve many substances.
Hydrogen Bonding: Responsible for water’s high specific heat, surface tension, and solvent abilities.
Solvent Properties: Facilitates chemical reactions by dissolving ionic and polar substances.

Chemical Bonds

Ionic Bonds: Formed by the transfer of electrons between atoms, resulting in charged ions (e.g., NaCl).
Covalent Bonds: Atoms share electrons; strong and common in organic molecules (e.g., H2O, CH4).
Hydrogen Bonds: Weak bonds between a hydrogen atom and an electronegative atom (e.g., between water molecules).

Hydrolysis and Dehydration Synthesis Reactions

Hydrolysis: Breaking down complex molecules by adding water.
Dehydration Synthesis: Joining two molecules by removing water.
Example: Formation and breakdown of macromolecules such as proteins and polysaccharides.

Properties of Carbon Chains

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

Versatility: Can form straight, branched, or ring structures.
Functional Groups: Attachments such as hydroxyl, carboxyl, amino, and phosphate groups determine chemical reactivity.

Macromolecules

Carbohydrates: Energy source and structural components. Monomer: Monosaccharides (e.g., glucose). Polymer: Polysaccharides (e.g., starch, cellulose).
Lipids: Energy storage, membrane structure. Types: Fats, phospholipids, steroids. Structure: Glycerol + fatty acids.
Proteins: Enzymes, structural roles, transport. Monomer: Amino acids. Structure: Primary, secondary, tertiary, quaternary.
Nucleic Acids: Genetic information storage and transfer. Monomer: Nucleotides. Types: DNA, RNA.

Example: DNA is composed of nucleotides with a sugar-phosphate backbone and nitrogenous bases.

Ch. 3 – Observing Microorganisms Through a Microscope

Staining Procedures

Staining enhances contrast in microscopic specimens, making cellular structures visible.

Simple Stain: Uses a single dye to highlight the entire organism.
Gram Stain: Differentiates bacteria into Gram-positive and Gram-negative based on cell wall structure.

Gram Stain Steps

Crystal violet (primary stain)
Iodine (mordant)
Alcohol (decolorizer)
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 of transparent specimens.
Darkfield Microscope: Visualizes live, thin organisms; background appears dark.
Fluorescence Microscope: Detects fluorescently labeled structures; useful for specific identification.
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-shaped

Plasma Membrane

Structure: Phospholipid bilayer with embedded proteins.
Function: Selective barrier, transport, energy generation.

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

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; no energy required.
Active Transport: Movement against gradient; requires energy (ATP).

Endosymbiotic Theory

Explains the origin of eukaryotic organelles (mitochondria, chloroplasts) from prokaryotic ancestors.

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

Ch. 5 & 6 – Microbial Metabolism and Growth

Microbial Nutrition Types

Chemoautotrophs: Use inorganic chemicals for energy, CO2 as carbon source.
Chemoheterotrophs: Use organic compounds for energy and carbon.
Photoautotrophs: Use light for energy, CO2 as carbon source.
Photoheterotrophs: Use light for energy, organic compounds for carbon.

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.
Aerobes: Require oxygen.
Anaerobes: Cannot tolerate oxygen.
Facultative Anaerobes: Grow with or without 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:

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).

Electron Transport Chain (ETC)

Function: Transfers electrons to generate ATP via oxidative phosphorylation.

Ch. 7 – Control of Microbial Growth

Physical Methods

Autoclave: Uses steam under pressure to sterilize (121°C, 15 psi, 15 min).
Gamma Radiation: Damages DNA, sterilizes heat-sensitive items.
Microwaves: Kills by heat; uneven heating may not sterilize.
Sunlight: Contains UV; limited germicidal effect.
Ultraviolet Radiation: Damages DNA (thymine dimers); used for surface sterilization.

Chemical Agents

Chlorine: Oxidizes cellular components; disinfects water.
Glutaraldehyde: Cross-links proteins; sterilizes medical equipment.
Hydrogen Peroxide: Oxidizing agent; disinfects surfaces and wounds.
Iodine: Disrupts proteins; antiseptic for skin.
Ozone: Oxidizes cell components; disinfects air and water.

Mechanisms of Action

Disruption of plasma membranes (e.g., alcohols, detergents).
Protein denaturation (e.g., heat, aldehydes).
Oxidation of cellular components (e.g., chlorine, hydrogen peroxide).

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 copied by DNA polymerase.
Transcription: DNA transcribed to mRNA by RNA polymerase.
Translation: mRNA translated to protein by ribosomes.
Transformation: Uptake of naked DNA from environment (Griffith’s experiment).

Replica Plating

Technique to isolate mutants by transferring colonies to different 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

Operon Model of Gene Regulation

Inducible Genes: Turned on in response to substrate (e.g., lac operon).
Repressible Genes: Turned off when end product is abundant (e.g., trp operon).
Micro RNAs: Regulate gene expression post-transcriptionally.

Effects of Radiation on DNA

Ionizing Radiation: Breaks DNA strands (e.g., X-rays, gamma rays).
UV Radiation: Causes thymine dimers, leading to mutations.

Mutations

Substitution: One base replaced by another; may alter protein.
Frameshift: Insertion or deletion shifts reading frame; usually severe effect.

Griffith’s Experiments

Demonstrated transformation: non-virulent bacteria became virulent by acquiring DNA from dead virulent cells.

Example: Streptococcus pneumoniae transformation in mice.