Microbiology Study Guide: Foundations, Cell Biology, and Microbial Diversity

Introduction to Microbiology

Defining Life and Its Characteristics

Microbiology explores the study of microscopic organisms and their fundamental properties. Understanding what constitutes life is essential for distinguishing living from non-living entities.

• Main Characteristics of Life: All living organisms possess a plasma membrane, DNA (genetic material), ribosomes (for protein synthesis), and cytosol (cellular fluid).

• Three Domains of Life: Bacteria, Archaea, and Eukarya. Organisms are named using binomial nomenclature (Genus species).

• Prokaryotes vs. Eukaryotes: Prokaryotes lack a nucleus and membrane-bound organelles; eukaryotes possess both.

• Main Groups of Microorganisms: Living: Bacteria, Archaea, fungi, protozoa, algae, helminths. Non-living: viruses (acellular), viroids, prions.

• Viruses: Acellular entities, considered non-living by many due to lack of cellular structure and independent metabolism.

Biomolecules: The Chemistry of Biology

Chemical Bonds and Subatomic Particles

Biological molecules are formed through chemical bonds involving subatomic particles.

• Subatomic Particles: Protons, neutrons, and electrons. Valence electrons are electrons in the outer shell, crucial for bond formation.

• Types of Chemical Bonds:

  • Covalent Bonds: Sharing of electrons. Polar covalent (unequal sharing, e.g., H2O), non-polar covalent (equal sharing, e.g., O2).

  • Non-covalent Bonds: Hydrogen bonds (weak, between polar molecules), ionic bonds (transfer of electrons).

• Hydration Shell: Water molecules surround ions (cations/anions), stabilizing them in solution.

Key Chemical Reactions

• Dehydration Synthesis: Formation of larger molecules by removing water.

• Hydrolysis: Breakdown of molecules by adding water.

• Catabolic Reactions: Breakdown of complex molecules; anabolic reactions: synthesis of complex molecules.

pH Scale

• pH: Measures hydrogen ion concentration; scale ranges from 0 (acidic) to 14 (basic), with 7 as neutral.

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

Organic Macromolecules

Cells are composed of four main types of macromolecules, each with unique structure and function.

• Carbohydrates: Energy storage and structural support; composed of monosaccharides linked by glycosidic bonds.

• Lipids: Membrane structure and energy storage; hydrophobic, include phospholipids (amphipathic), triglycerides, and steroids.

• Proteins: Enzymes, structural components; made of amino acids linked by peptide bonds.

• Nucleic Acids: DNA and RNA; store and transmit genetic information, composed of nucleotides linked by phosphodiester bonds.

• Enantiomers: Molecules that are mirror images; important in biochemistry (e.g., amino acids).

• Functional Groups: Specific groups of atoms (e.g., hydroxyl, carboxyl) that determine chemical properties.

• Hydrophilic vs. Hydrophobic: Hydrophilic molecules interact with water; hydrophobic molecules repel water (e.g., phospholipid tails).

Cell Structure and Function

Koch’s Postulates and Pathogens

Koch's postulates are criteria for establishing a causative relationship between a microbe and a disease.

• Microbe must be found in all cases of the disease.

• Microbe must be isolated and grown in pure culture.

• Pure culture must cause disease when introduced to a healthy host.

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

Cell Components

• Plasma Membrane: Selective barrier, composed of phospholipid bilayer.

• DNA: Genetic material, located in nucleoid (prokaryotes) or nucleus (eukaryotes).

• Ribosomes: Protein synthesis machinery.

• Cytosol: Fluid matrix of the cell.

Bacterial Shapes and Arrangements

• Cocci: Spherical

• Bacilli: Rod-shaped

• Strepto-: Chains

• Staphylo-: Clusters

Prokaryotic Structural Features

• Glycocalyces: Protective layers; capsules (organized, prevent phagocytosis), slime layers (loose, aid in adhesion).

• Fimbriae: Attachment structures.

• Flagella: Motility; arrangements include monotrichous, lophotrichous, amphitrichous, peritrichous.

• Pili: Conjugation and attachment.

• Bacterial Cell Walls: Gram-positive (thick peptidoglycan, teichoic acids), Gram-negative (thin peptidoglycan, outer membrane), mycolic acid (acid-fast bacteria).

• Endospores: Resistant structures for survival under harsh conditions.

Membrane Transport

• Passive Transport: Diffusion, facilitated diffusion, osmosis.

• Active Transport: Requires energy (ATP), moves substances against concentration gradient.

• Solution Types: Hypertonic (water leaves cell), hypotonic (water enters cell), isotonic (no net movement).

Cell Walls and Membranes: Prokaryotes vs. Eukaryotes

• Prokaryotic Cell Walls: Peptidoglycan (Bacteria), pseudopeptidoglycan (Archaea).

• Eukaryotic Cell Walls: Cellulose (plants, algae), chitin (fungi), absent in animals and protozoa.

• Membranes: Both have phospholipid bilayers; eukaryotes may have sterols (cholesterol).

Eukaryotic Organelles

• Nucleus: Contains DNA.

• Mitochondria: ATP production.

• Endoplasmic Reticulum: Protein and lipid synthesis.

• Golgi Apparatus: Protein modification and sorting.

• Lysosomes: Digestion of cellular waste.

Comparison of the Three Domains of Life

• Bacteria: Prokaryotic, peptidoglycan cell walls, diverse metabolism.

• Archaea: Prokaryotic, unique cell wall chemistry, extremophiles.

• Eukarya: Eukaryotic, membrane-bound organelles, includes plants, animals, fungi, and protists.

Prokaryotes: Diversity and Reproduction

Types of Symbiosis

• Mutualism: Both organisms benefit.

• Commensalism: One benefits, other unaffected.

• Amensalism: One harmed, other unaffected.

• Parasitism: One benefits, other harmed.

Prokaryotic Reproduction

• Binary Fission: Most common, cell divides into two.

• Snapping Division: Variation of binary fission.

• Spore Formation: Some bacteria and fungi form spores for reproduction.

• Budding: New organism grows from parent.

Survey of Archaea and Bacteria

• Archaea: Includes extremophiles (halophiles: salt-loving, thermophiles: heat-loving), methanogens (produce methane).

• Bacteria: Four main groupings:

  • Deeply Branching Bacteria

  • Gram-positive Bacteria

  • Gram-negative Bacteria

  • Phototrophic Bacteria

• Autotrophic: Organisms that produce their own food from inorganic sources.

Eukaryotes: Diversity and Reproduction

General Characteristics

• Membrane-bound organelles, nucleus, complex structure.

Key Terms and Processes

• Haploid: One set of chromosomes.

• Diploid: Two sets of chromosomes.

• Coenocytes: Multinucleate cells.

• Schizogony: Asexual reproduction by multiple fission.

• Mitosis vs. Meiosis: Mitosis produces identical cells; meiosis produces gametes with half the chromosome number.

Survey of Eukaryotic Microorganisms

• Protozoa: Unicellular, lack cell walls, mostly chemoheterotrophs.

• Fungi: Chemoheterotrophs, cell walls of chitin, reproduce sexually or asexually.

• Algae: Photoautotrophs, unicellular or multicellular, reproduce by alternation of generations.

• Helminths: Parasitic worms, important in disease.

• Vectors: Organisms (arachnids, insects) that transmit pathogens.

Viruses, Viroids, and Prions: Acellular Microbes

Characteristics and Structure of Viruses

• Acellular, composed of nucleic acid (DNA or RNA) and protein coat (capsid); some have lipid envelope.

• Obligate intracellular parasites; require host cell for replication.

Stages of Viral Replication

• Attachment: Virus binds to host cell.

• Penetration: Entry of viral genome.

• Synthesis: Host machinery produces viral components.

• Assembly: New virions are assembled.

• Release: Virions exit host cell.

Lysogeny, Latency, and Lytic Cycle

• Lytic Cycle: Virus replicates and destroys host cell.

• Lysogeny: Viral genome integrates into host DNA, remains dormant.

• Latency: Virus remains inactive within host cell.

Bacterial vs. Animal Viruses

• Bacteriophage: Infect bacteria; often undergo lytic or lysogenic cycles.

• Enveloped Viruses: Infect animals; envelope derived from host membrane.

Viroids and Prions

• Viroids: Small, circular RNA molecules; infect plants.

• Prions: Infectious proteins; cause neurodegenerative diseases (e.g., mad cow disease).

• Comparison: Prions lack nucleic acids; viruses contain nucleic acids and protein coat.

Microbe Type	Structure	Living/Non-living	Example
Bacteria	Prokaryotic cell, peptidoglycan wall	Living	Escherichia coli
Archaea	Prokaryotic cell, unique wall	Living	Halobacterium
Fungi	Eukaryotic cell, chitin wall	Living	Aspergillus
Protozoa	Eukaryotic, no cell wall	Living	Plasmodium
Algae	Eukaryotic, cellulose wall	Living	Chlamydomonas
Helminths	Multicellular eukaryotes	Living	Schistosoma
Viruses	Acellular, nucleic acid + protein coat	Non-living	Influenza virus
Viroids	RNA only	Non-living	Potato spindle tuber viroid
Prions	Protein only	Non-living	Creutzfeldt-Jakob disease agent

Example: The lytic cycle of bacteriophage T4 involves attachment to E. coli, injection of DNA, synthesis of viral components, assembly, and release by cell lysis.

Additional info: Academic context was added to expand brief points into full explanations, and to clarify terms and processes for exam preparation.