Microbiology Exam 1 Study Guide: Key Concepts and Foundations

Introduction to Microbiology

Definition and Scope

Microbiology is the study of microscopic organisms, including bacteria, viruses, fungi, protists, and archaea. It encompasses various fields such as medical microbiology, environmental microbiology, industrial microbiology, and immunology.

• Microbes can be both helpful and harmful. They play essential roles in nutrient cycling, food production, and biotechnology, but some cause diseases.

• Microorganisms cause disease by invading host tissues, producing toxins, or triggering immune responses.

Types of Microorganisms

• Prokaryotic: Bacteria and Archaea (lack a nucleus and membrane-bound organelles)

• Eukaryotic: Protists, Fungi, Plants, Animals (have a nucleus and organelles)

Classification and Naming

• Microbes are classified based on morphology, genetic analysis, and biochemical characteristics.

• Naming follows binomial nomenclature: Genus species (e.g., Escherichia coli).

Historical Theories and Figures

• Spontaneous Generation: The outdated theory that life arises from non-living matter.

• Germ Theory: Diseases are caused by microorganisms.

• Key contributors: van Leeuwenhoek (microscopy), Pasteur (disproved spontaneous generation), Koch (postulates), Snow (epidemiology), Lister (antiseptics), Fleming (penicillin).

Roles of Microorganisms

• In the human body: digestion, immunity, disease.

• In the environment: decomposition, nutrient cycling.

Microscopy

Size Ranges and Visualization

Microscopy is essential for observing microorganisms due to their small size.

• Bacteria: 0.5–5 μm

• Viruses: 20–300 nm

• Protists: 10–100 μm

• Light microscopes are used for bacteria and protists; electron microscopes for viruses.

Staining Techniques

• Staining increases contrast for visualization.

• General stains color all cells; Gram stain differentiates Gram-positive (purple) and Gram-negative (pink) bacteria.

• Gram stain differences are due to cell wall structure: thick peptidoglycan in Gram-positive, thin in Gram-negative.

Chemistry of Microbiology

Chemical Bonds and Solutions

• Ionic bonds: transfer of electrons.

• Covalent bonds: sharing of electrons.

• Hydrogen bonds: weak attraction between polar molecules.

• Solvent: substance that dissolves another; solute: substance dissolved.

Metabolism and Reactions

• Catabolism: breakdown of molecules, releases energy (exergonic).

• Anabolism: synthesis of molecules, requires energy (endergonic).

Polarity and pH

• Polar substances: uneven charge distribution, dissolve in water.

• Nonpolar substances: even charge distribution, do not dissolve in water.

• pH: measures acidity/basicity. Acid (pH < 7), base (pH > 7), neutral (pH = 7).

Functional Groups

• Hydroxyl (-OH), methyl (-CH3), amino (-NH2), carboxyl (-COOH), phosphate (-PO4).

Carbohydrates

• Monosaccharides: single sugar units (e.g., glucose).

• Disaccharides: two sugars (e.g., sucrose).

• Polysaccharides: many sugars (e.g., starch, cellulose).

• Other types: glycolipids, glycoproteins, proteoglycans (carbohydrates attached to lipids/proteins).

Lipids

• Lipid bilayer forms cell membranes.

• Hydrophilic: water-loving; hydrophobic: water-fearing.

• Saturated fats: no double bonds; unsaturated fats: one or more double bonds.

• Amphipathic molecules: have both hydrophilic and hydrophobic regions (e.g., phospholipids).

• Sterols (e.g., cholesterol) stabilize membranes.

Proteins

• Proteins are nitrogenous organic molecules made of amino acids.

• R-groups determine amino acid properties.

• Peptide bond: links amino acids.

• Proteins have four structural levels: primary (sequence), secondary (helix/sheet), tertiary (3D folding), quaternary (multiple chains).

• Conjugated proteins: glycoproteins, lipoproteins, nucleoproteins, metalloproteins (contain sugars, lipids, nucleic acids, metals).

Nucleic Acids

• DNA and RNA are genetic biomolecules.

• Complementary base pairing: A::T, C:::G in DNA; A::U, C:::G in RNA.

• DNA encodes genetic information.

• Griffith's experiment showed transformation in bacteria.

ATP

• ATP is the cell's energy currency, used for metabolic processes.

Enzymes

• Enzymes are biological catalysts that speed up reactions by lowering activation energy.

• Structure: active site binds substrate; products are released.

• Components: cofactors (inorganic), coenzymes (organic).

• Factors affecting activity: temperature, pH, substrate concentration.

• Enzyme inhibitors block activity; allosteric sites regulate function.

Cell Structure and Function

Prokaryotes vs. Eukaryotes

• Prokaryotes: no nucleus, simple structure.

• Eukaryotes: nucleus, complex organelles.

Bacterial Shapes and Features

• Shapes: cocci (spherical), bacilli (rod-shaped), spirilla (spiral).

• Features: glycocalyx (protection), flagella (motility), fimbriae (attachment), pili (conjugation).

Gram Positive vs. Gram Negative Bacteria

• Gram-positive: thick peptidoglycan, teichoic acids, lipoteichoic acids.

• Gram-negative: thin peptidoglycan, outer membrane with LPS, lipoproteins, phospholipids.

• LPS provides structural integrity and protection.

Peptidoglycan Structure

• Made of N-acetylglucosamine and N-acetylmuramic acid linked by peptide chains.

• Provides cell wall strength; present in both Gram-positive and Gram-negative bacteria.

• Gram-positive: thick layer; Gram-negative: thin layer.

Bacterial Cytosol and Structures

• Nucleoid: DNA region.

• Plasmids: extra-chromosomal DNA.

• Ribosomes: protein synthesis.

Endospores

• Resistant structures for survival under harsh conditions.

Cytoplasmic Membrane

• Structure: phospholipid bilayer.

• Function: selective permeability, transport.

Transport Mechanisms

• Osmosis: movement of water across membrane.

• Osmotic pressure: force exerted by water movement.

• Simple diffusion: passive movement down concentration gradient.

• Facilitated diffusion: passive movement via transport proteins.

• Isotonic: equal solute; hypotonic: lower solute outside; hypertonic: higher solute outside.

• Passive transport: no energy; active transport: requires energy (usually ATP).

Eukaryotic Cell Features

• Flagella, cilia: movement.

• Glycocalyx: protection.

• Cytoplasmic membrane: similar to prokaryotes.

• Organelles: specialized functions; DNA in nucleus.

Microbial Growth

Physical Requirements

• Temperature: microbes have optimal ranges (psychrophiles, mesophiles, thermophiles).

• pH: most prefer neutral, some thrive in acidic or basic conditions.

• Osmotic pressure: affects water availability.

Chemical Requirements

• Carbon source: organic or inorganic.

• Essential elements: nitrogen, sulfur, phosphorus.

• Oxygen requirements:

  • Obligate aerobes: require oxygen.

  • Obligate anaerobes: cannot tolerate oxygen.

  • Facultative anaerobes: can grow with or without oxygen.

Summary Table: Gram Positive vs. Gram Negative Bacteria

Feature	Gram Positive	Gram Negative
Peptidoglycan Layer	Thick	Thin
Teichoic Acids	Present	Absent
Lipopolysaccharide (LPS)	Absent	Present
Outer Membrane	Absent	Present
Stain Color	Purple	Pink

Key Equations

• pH calculation: $pH = -\log_{10}[H^+]$

• ATP hydrolysis: $ATP + H_2O \rightarrow ADP + P_i + \text{energy}$

Example: Escherichia coli is a Gram-negative bacterium with a thin peptidoglycan layer and an outer membrane containing LPS.

Example: The Gram stain is used to differentiate bacteria based on cell wall structure, aiding in diagnosis and treatment selection.

Example: ATP is used by cells to drive active transport across membranes, such as the sodium-potassium pump.