Microbiology Exam 1 Study Guide: Foundations, Cell Structure, and Genetics

Chapter 1: Introduction to Microbiology

Definition and Types of Microorganisms

Microorganisms are microscopic organisms, often too small to be seen with the naked eye. They include both living and non-living entities.

• Types of Microbes:

  • Living: Bacteria, Archaea, Fungi, Protozoa, Algae, Helminths (parasitic worms)

  • Non-living: Viruses, Prions (infectious proteins)

• Pathogen: A microorganism that causes disease.

• Opportunistic Pathogen: Normally harmless but can cause disease in a compromised host.

Biogenesis vs. Spontaneous Generation

These are two historical theories about the origin of life.

• Biogenesis: Life arises from pre-existing life.

• Spontaneous Generation: Life can arise from non-living matter.

• Louis Pasteur: Disproved spontaneous generation with his swan-neck flask experiment, supporting biogenesis.

Germ Theory and Koch's Postulates

• Germ Theory of Disease: Proposed by Robert Koch, states that specific microbes cause specific diseases.

• Koch's Postulates: Criteria to establish a causative relationship between a microbe and a disease:

  1. The microorganism must be found in all organisms suffering from the disease, but not in healthy organisms.

  2. The microorganism must be isolated and grown in pure culture.

  3. The cultured microorganism should cause disease when introduced into a healthy organism.

  4. The microorganism must be re-isolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.

Aseptic Technique

• Aseptic Technique: Procedures to prevent contamination by unwanted microorganisms, crucial in healthcare and laboratory settings.

Scientific Method

• Steps: Observation, Question, Hypothesis, Experiment, Data Collection, Conclusion, Theory/Law.

• Observation: Gathering information using senses or instruments.

• Hypothesis: Testable explanation for an observation.

• Theory: Well-substantiated explanation based on evidence.

• Law: Statement describing consistent natural phenomena.

Taxonomy and Classification

• Taxonomic Hierarchy: Domain > Kingdom > Phylum > Class > Order > Family > Genus > Species

• Three Domains: Bacteria, Archaea, Eukarya

• Six Kingdoms: Bacteria, Archaea, Protista, Fungi, Plantae, Animalia

• Binomial Nomenclature: Two-part scientific naming system (Genus species), e.g., Escherichia coli

• Strain: Genetic variant or subtype of a microorganism.

Microbial Interactions and Microbiota

• Parasitism: One organism benefits, the other is harmed.

• Mutualism: Both organisms benefit.

• Commensalism: One benefits, the other is unaffected.

• Normal Microbiota: Microbes that normally inhabit the human body without causing disease.

• Biofilms: Communities of microbes attached to surfaces, encased in a protective matrix.

Microbes in Industry and Environment

• Examples: Fermentation (food production), bioremediation (pollutant breakdown), antibiotic production.

Laboratory Techniques

• Streak Plate Technique: Method to isolate pure colonies of bacteria on agar plates.

• Colony: Visible mass of microbial cells derived from a single cell.

Staining and Microscopy

• Simple Stain: Uses one dye to highlight cells.

• Structural Stain: Highlights specific cell structures (e.g., endospores, capsules).

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

• Acid-Fast Stain: Identifies acid-fast bacteria (e.g., Mycobacterium species).

• Microscope Types: Light microscope, electron microscope, fluorescence microscope.

Chapter 2 (Section 2.4): Biochemistry Basics

Biomolecules and Their Building Blocks

• Carbohydrates: Monosaccharides (simple sugars); provide energy and structural support in microbes.

• Lipids: Fatty acids and glycerol; form membranes and store energy.

• Proteins: Amino acids; serve as enzymes, structural components, and signaling molecules.

• Nucleic Acids: Nucleotides; store and transmit genetic information (DNA, RNA).

Carbohydrates in Microbes

• Serve as energy sources and structural components (e.g., peptidoglycan in bacterial cell walls).

Lipids in Microbes

• Form cell membranes (phospholipids), energy storage (triglycerides), and signaling molecules.

Protein Functions

• Enzymes, transport, structural support, movement, defense, regulation.

Amino Acids

• Building blocks of proteins; 20 standard amino acids.

Nucleic Acids

• DNA and RNA; composed of nucleotides (sugar, phosphate, nitrogenous base).

DNA vs. RNA

• DNA: Double-stranded, deoxyribose sugar, bases A-T, G-C.

• RNA: Single-stranded, ribose sugar, bases A-U, G-C.

Chemical Bonds in Biomolecules

• Glycosidic Bond: Joins monosaccharides in carbohydrates.

• Peptide Bond: Joins amino acids in proteins.

• Phosphodiester Bond: Joins nucleotides in nucleic acids.

Chapter 3: Introduction to Prokaryotic Cells

Prokaryotic Domains and Cell Structure

• Domains: Bacteria and Archaea.

• Prokaryotic Cell Structure: Lack membrane-bound organelles; have cell membrane, cell wall, cytoplasm, ribosomes, nucleoid.

• Small Size: Increases surface area-to-volume ratio, aiding nutrient uptake and waste removal.

Shapes and Arrangements

• Shapes: Cocci (spherical), Bacilli (rod-shaped), Spirilla (spiral).

• Arrangements: Chains (strepto-), clusters (staphylo-), pairs (diplo-).

Binary Fission

• Method of asexual reproduction in prokaryotes; cell divides into two identical daughter cells.

Cell Membrane and Cell Wall

• Cell Membrane: Phospholipid bilayer with proteins; controls entry/exit of substances.

• Cell Wall: Provides shape and protection; composition varies (peptidoglycan in bacteria).

Membrane Fluidity and Mosaic Structure

• Fluid Mosaic Model: Membrane is flexible, with proteins embedded in a phospholipid bilayer.

• Temperature Effects: High temperatures increase fluidity; low temperatures decrease it.

• Saturation: Unsaturated fatty acids increase fluidity; saturated decrease it.

Gram-Positive vs. Gram-Negative Cell Walls

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

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

Acid-Fast Positive Cells

• Resistant to certain drugs due to waxy cell wall (mycolic acid); important in clinical diagnosis (e.g., Mycobacterium tuberculosis).

Transport Mechanisms

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

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

• Diffusion: Movement from high to low concentration; simple (direct) or facilitated (via proteins).

• Osmosis: Diffusion of water across a semipermeable membrane.

• Osmotic Environments:

  • Hypertonic: Water leaves cell; cell shrinks.

  • Hypotonic: Water enters cell; cell may burst.

  • Isotonic: No net water movement.

External Structures of Prokaryotic Cells

• Flagella: Tail-like structures for movement.

• Fimbriae: Short, hair-like structures for attachment.

• Pili: Longer, involved in attachment and DNA transfer (conjugation).

• Glycocalyx: Capsule or slime layer; protects against desiccation and immune response.

Internal Structures

• Nucleoid: Region containing the bacterial chromosome (DNA).

• Ribosomes: Sites of protein synthesis.

• Cytoskeleton: Protein filaments for shape and support.

• Inclusion Bodies: Storage sites for nutrients and other substances.

Endospores

• Dormant, tough structures formed by some bacteria (e.g., Bacillus, Clostridium); highly resistant to heat, chemicals, and desiccation.

• Pose challenges in healthcare due to resistance to sterilization.

Chapter 5: Genetics

Genome Organization

• Genome: Complete set of genetic material in an organism.

• Gene: Segment of DNA coding for a functional product.

• Genotype: Genetic makeup of an organism.

• Phenotype: Observable traits resulting from genotype.

• Genome Organization:

  • Viruses: DNA or RNA, single or double-stranded.

  • Prokaryotes: Single circular chromosome, plasmids.

  • Eukaryotes: Multiple linear chromosomes in nucleus.

• Plasmid: Small, circular DNA molecule in prokaryotes; often carries antibiotic resistance genes.

DNA Structure and Replication

• Nitrogen Bases in DNA: Adenine (A), Thymine (T), Guanine (G), Cytosine (C); A pairs with T, G with C.

• DNA Composition: Double helix of nucleotides; sugar-phosphate backbone, bases inside.

• Central Dogma: Information flows from DNA → RNA → Protein.

• DNA Replication: Semiconservative process; each new DNA has one old and one new strand.

• Enzymes in Replication:

  • Helicase: Unwinds DNA.

  • DNA Polymerase: Synthesizes new DNA strand.

  • Primase: Synthesizes RNA primer.

  • Ligase: Joins DNA fragments.

• Leading Strand: Synthesized continuously.

• Lagging Strand: Synthesized in Okazaki fragments.

• Prokaryotic vs. Eukaryotic Replication: Prokaryotes have one origin of replication; eukaryotes have multiple.

Gene Expression

• Two Main Processes: Transcription (DNA to RNA), Translation (RNA to protein).

• Transcription: Synthesis of RNA from DNA template.

• Reverse Transcription: Synthesis of DNA from RNA (e.g., retroviruses).

• Genetic Code: Triplet codons specify amino acids; universal and redundant.

• Three RNA Types: mRNA (messenger), tRNA (transfer), rRNA (ribosomal).

• Translation: Ribosomes synthesize proteins using mRNA template.

• Post-Translational Modifications: Chemical changes to proteins after synthesis (e.g., phosphorylation).

• Constitutive Genes: Always expressed.

• Facultative Genes: Expressed as needed.

Mutations

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

• Insertion/Deletion: Addition or loss of bases; may cause frameshift mutations, altering protein sequence.

• Spontaneous Mutations: Occur naturally during DNA replication.

• Induced Mutations: Caused by mutagens (chemicals, radiation).

• Classes of Mutagens: Chemical (e.g., base analogs), physical (e.g., UV light), biological (e.g., transposons).

Gene Transfer in Prokaryotes

• Vertical Gene Transfer: Parent to offspring.

• Horizontal Gene Transfer: Between organisms, not by descent.

• Conjugation: Direct transfer of DNA via pilus; steps include donor cell attachment, pilus formation, DNA transfer.

• Transformation: Uptake of free DNA from environment.

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

Gene Transfer Method	Mechanism	Key Features
Conjugation	Direct cell-to-cell contact via pilus	Plasmid transfer, requires donor and recipient
Transformation	Uptake of naked DNA from environment	Competent cells required
Transduction	DNA transfer by bacteriophage	Generalized or specialized

Example: Antibiotic resistance genes can spread rapidly among bacteria via horizontal gene transfer.

Additional info: For equations such as the central dogma, use: $DNA \rightarrow RNA \rightarrow Protein$