Chemical Principles of Microbiology

Chemical Bonds

Chemical bonds are the forces that hold atoms together in molecules and compounds, playing a crucial role in the structure and function of biological molecules.

• Ionic Bonds: Formed when electrons are transferred from one atom to another, resulting in charged ions (e.g., NaCl).

• Covalent Bonds: Atoms share pairs of electrons; these are strong and common in organic molecules (e.g., H2O, DNA backbone).

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

• Importance: The type and arrangement of bonds determine the properties and functions of biological macromolecules.

Biological Macromolecules

Macromolecules are large, complex molecules essential for life, including DNA, proteins, lipids, and carbohydrates.

• DNA: Stores genetic information; composed of nucleotides (A, T, G, C).

• Proteins: Made of amino acids; function as enzymes, structural components, and signaling molecules.

• Lipids: Hydrophobic molecules; form cell membranes and store energy.

• Carbohydrates: Sugars and polysaccharides; provide energy and structural support.

• Example: Phospholipids form the bilayer of cell membranes.

Microscopes

Light Microscopy and Compound Microscope

Light microscopy uses visible light to observe specimens, with the compound microscope being the most common type in microbiology labs.

• Compound Microscope: Uses multiple lenses to magnify specimens up to 1000x.

• Parts: Ocular lens, objective lenses, stage, condenser, light source.

• Resolution: Ability to distinguish two points as separate; limited by the wavelength of light.

• Application: Observing stained bacteria, cell morphology, and arrangements.

Preparation of Specimens for Light Microscopy

• Fixation: Preserves cell structure (heat or chemical methods).

• Staining: Enhances contrast (e.g., Gram stain, simple stain).

• Smear Preparation: Thin film of specimen spread on slide and fixed.

Prokaryotic Cell Structures & Functions

Structure of Prokaryotic Cell

Prokaryotic cells, such as bacteria, lack a nucleus and membrane-bound organelles.

• Cell Wall: Provides shape and protection; composed of peptidoglycan in bacteria.

• Plasma Membrane: Selectively permeable barrier.

• Cytoplasm: Contains ribosomes, DNA (nucleoid), and inclusions.

• Flagella: For motility.

• Pili/Fimbriae: Attachment and conjugation.

Gram Positive and Gram Negative Bacteria

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

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

Gram Stain

• Steps: Crystal violet, iodine, alcohol decolorization, safranin counterstain.

• Purpose: Differentiates bacteria based on cell wall structure.

Cell Membrane & Transport

Movement of Materials Across Membranes

• Passive Transport: No energy required (diffusion, facilitated diffusion, osmosis).

• Active Transport: Requires energy (ATP) to move substances against concentration gradient.

• Example: Uptake of nutrients, expulsion of waste.

Dynamics of Microbial Growth

Reproduction of Prokaryotes

• Binary Fission: Main method; cell divides into two identical daughter cells.

• Generation Time: Time required for a population to double.

Phases of Growth

• Lag Phase: Adaptation, no division.

• Log (Exponential) Phase: Rapid cell division.

• Stationary Phase: Nutrient depletion, growth rate slows.

• Death Phase: Cells die faster than they divide.

Methods of Counting Bacteria

• Direct Count: Microscopic count, viable plate count.

• Indirect Count: Turbidity measurement, metabolic activity.

Serial Dilutions and Plate Count

• Serial Dilution: Stepwise dilution of a sample to reduce cell concentration for counting.

• Plate Count: Counting colonies to estimate viable cells in original sample.

• Formula:

Controlling Microbial Growth

Microbial Control Terminology and Methods

• Sterilization: Destruction of all microbial life.

• Disinfection: Elimination of most pathogens (not spores).

• Antisepsis: Disinfection of living tissue.

• Sanitization: Lowering microbial counts to safe levels.

• Methods: Heat (autoclaving, dry heat), filtration, radiation, chemical agents.

Disk-Diffusion Test

• Purpose: Assess effectiveness of antimicrobial agents.

• Method: Disks with chemicals placed on agar inoculated with bacteria; zone of inhibition measured.

Microbial Metabolism

Enzymes and Enzyme Inhibitors

• Enzymes: Biological catalysts that speed up reactions by lowering activation energy.

• Enzyme Inhibitors: Substances that decrease enzyme activity (competitive and noncompetitive inhibitors).

• Example: Sulfa drugs inhibit folic acid synthesis in bacteria.

Respiration and Fermentation

• Respiration: Complete oxidation of substrates with production of ATP; can be aerobic or anaerobic.

• Fermentation: Partial oxidation of substrates; less ATP produced; end products include acids, gases, alcohols.

Central Dogma & Gene Regulation

Replication, Transcription, Translation

• Replication: DNA is copied to produce identical DNA molecules.

• Transcription: DNA is transcribed into messenger RNA (mRNA).

• Translation: mRNA is decoded to synthesize proteins.

• Central Dogma:

Gene Regulation: Constitutive, Inducible, Repressible Genes

• Constitutive Genes: Expressed continuously (e.g., genes for glycolysis).

• Inducible Genes: Expressed only in presence of an inducer (e.g., lac operon).

• Repressible Genes: Expression can be turned off by a repressor (e.g., trp operon).

Microbial Genetics

Mutation

• Mutation: Permanent change in DNA sequence; can be spontaneous or induced.

• Types: Point mutations, insertions, deletions.

• Effects: May be beneficial, harmful, or neutral.

Horizontal Gene Transfer: Transformation, Conjugation, Transduction

• Transformation: Uptake of naked DNA from environment.

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

• Transduction: Transfer of DNA by bacteriophages (viruses that infect bacteria).

Example: Antibiotic resistance genes can spread rapidly via conjugation.

Additional info: Some explanations and examples were expanded for clarity and completeness based on standard microbiology curricula.