Microbiology Exam 2 Study Guide: Chapters 7–13

Chapter 7: Microbial Genetics and DNA Structure

Structure and Function of DNA

DNA (deoxyribonucleic acid) is the hereditary material in all living organisms. It encodes genetic information and directs cellular activities.

• Five Nitrogenous Bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G), and Uracil (U) (Uracil is found in RNA).

• Base Pairing: DNA bases pair via hydrogen bonds: A with T, and C with G. This is called complementary base pairing.

• Bonding: Bases bond to each other across the two DNA strands, forming the double helix structure.

Plasmids: Structure and Function

Plasmids are small, circular, double-stranded DNA molecules found in bacteria and some eukaryotes. They replicate independently of chromosomal DNA.

• Function: Plasmids often carry genes for antibiotic resistance, virulence factors, or metabolic pathways.

Eukaryotic vs. Prokaryotic Chromosomes

Chromosomes are structures that organize and store genetic material.

• Eukaryotic Chromosomes: Linear, multiple chromosomes located in the nucleus.

• Prokaryotic Chromosomes: Typically a single, circular chromosome located in the nucleoid region.

DNA Replication

DNA replication is the process by which a cell duplicates its DNA before cell division.

• Origin of Replication: The site where DNA replication begins.

• Enzymes: DNA polymerase, helicase, primase, ligase.

• Leading vs. Lagging Strand: The leading strand is synthesized continuously, while the lagging strand is synthesized in fragments (Okazaki fragments).

Genotype vs. Phenotype

The genotype is the genetic makeup of an organism, while the phenotype is the observable traits.

• Central Dogma of Genetics: DNA → RNA → Protein

Mutations

Mutations are changes in the DNA sequence. They can be spontaneous or induced by mutagens (e.g., UV light).

• Types: Point mutations, insertions, deletions.

• Effects: Can lead to changes in protein function or regulation.

Horizontal Gene Transfer

• Transformation: Uptake of naked DNA from the environment.

• Transduction: Transfer of DNA via bacteriophages.

• Conjugation: Direct transfer of DNA between bacteria via a pilus.

Chapter 9: Microbial Control and Disinfection

Sterilization, Disinfection, and Antisepsis

These are methods to control microbial growth and prevent infection.

• Sterilization: Complete destruction of all microorganisms, including spores.

• Disinfection: Elimination of most pathogenic microorganisms (not spores) on inanimate objects.

• Antisepsis: Reduction of microbial load on living tissue.

Degerming, Sanitization, Pasteurization

• Degerming: Removal of microbes from a limited area (e.g., skin before injection).

• Sanitization: Lowering microbial counts to safe public health levels.

• Pasteurization: Heat treatment to kill pathogens and reduce spoilage organisms.

Microbial Death Rate

The rate at which microbes are killed by antimicrobial agents.

• Factors: Number of microbes, environment, time of exposure, microbial characteristics.

Physical and Chemical Methods of Microbial Control

• Physical Methods: Heat, filtration, radiation.

• Chemical Methods: Disinfectants, antiseptics, antibiotics.

Antimicrobial Chemicals: Major Types and Methods of Action

• Methods of Action: Disruption of cell membranes, denaturation of proteins, inhibition of metabolic pathways.

• Limitation: Many disinfectants are less effective against spores and some viruses.

Microbial Resistance

• Most Resistant: Prions, bacterial endospores.

• Least Resistant: Enveloped viruses, most Gram-positive bacteria.

Microbe Type	Resistance Level
Prions	Most resistant
Bacterial Endospores	Very resistant
Mycobacteria	Resistant
Enveloped Viruses	Least resistant

Chapter 10: Antimicrobial Drugs

Antimicrobial Drug Mechanisms

Antimicrobial drugs target specific structures or functions in microbes.

• Mechanisms: Inhibition of cell wall synthesis, protein synthesis, nucleic acid synthesis, metabolic pathways, and disruption of cell membranes.

• Examples: Penicillins (cell wall), tetracyclines (protein synthesis).

Broad-Spectrum vs. Narrow-Spectrum Drugs

• Broad-Spectrum: Effective against a wide range of microbes; higher risk of resistance and side effects.

• Narrow-Spectrum: Target specific microbes; lower risk of resistance.

Kirby-Bauer Test, Etest, MIC, MBC

• Kirby-Bauer Test: Disk diffusion method to assess antibiotic effectiveness.

• Etest: Determines minimum inhibitory concentration (MIC).

• MIC: Lowest concentration of drug that inhibits growth.

• MBC: Lowest concentration that kills the microbe.

Antimicrobial Resistance

• Causes: Overuse/misuse of antibiotics, genetic mutations, horizontal gene transfer.

• Plasmids: Can carry resistance genes.

• Cross-Resistance: Resistance to multiple drugs due to shared mechanisms.

• Synergism: Combined effect of drugs is greater than individual effects.

Chapter 11: Microbial Diversity and Ecology

Prokaryotic Cell Morphology and Arrangement

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

• Arrangements: Chains, clusters, pairs.

Bacterial Endospores

• Function: Survival under harsh conditions.

Archaea and Extremophiles

• Archaea: Domain of prokaryotes distinct from bacteria; often extremophiles.

• Types: Halophiles (salt-loving), thermophiles (heat-loving).

Phylum Characteristics

• Bacillota, Actinomycetota, Pseudomonadota, Chlamydiota, Spirochaetota, Bacteroidota: Each phylum has unique features and environmental roles.

Chapter 12: Eukaryotic Microbes and Reproduction

Eukaryotic Reproduction

• Mitosis: Cell division resulting in two identical daughter cells.

• Meiosis: Cell division producing gametes with half the chromosome number.

• Chromosomes: Structures containing DNA; eukaryotes have multiple, linear chromosomes.

• Centromeres and Spindle Fibers: Involved in chromosome movement during cell division.

• Haploid vs. Diploid: Haploid cells have one set of chromosomes; diploid cells have two sets.

Fungi

• Characteristics: Eukaryotic, cell walls of chitin, heterotrophic.

• Distinguishing Features: Hyphae, spores, unique reproductive cycles.

• Dimorphism: Ability to exist in both yeast and mold forms.

• Beneficial Uses: Antibiotic production, food fermentation.

Protozoa and Helminths

• Protozoa: Unicellular, motile, diverse life cycles.

• Helminths: Parasitic worms; multicellular.

Vector-Borne Diseases

• Vectors: Organisms (e.g., fleas, ticks, mosquitoes) that transmit pathogens.

• Emerging Diseases: New cases in previously unaffected areas due to environmental changes.

Chapter 13: Viruses and Prions

Virus Structure and Function

• Definition: Viruses are acellular infectious agents composed of genetic material (DNA or RNA) surrounded by a protein coat (capsid).

• Envelope: Some viruses have a lipid envelope derived from host membranes.

• Bacteriophage: Viruses that infect bacteria.

Host Specificity

• Specificity: Viruses attach to specific host cell receptors.

Viral Replication Cycles

• Lytic Cycle: Virus replicates and lyses host cell.

• Lysogenic Cycle: Viral genome integrates into host DNA and replicates with it.

• Attachment, Entry, Uncoating: Steps in viral infection.

Baltimore Classification

• Seven Classes: Based on type of nucleic acid and replication strategy.

Prions

• Definition: Infectious proteins causing neurodegenerative diseases.

• Diseases: Creutzfeldt-Jakob disease, mad cow disease.

Additional info: These notes expand on the study guide points with academic context, definitions, and examples for clarity and completeness.