Unit 1 Study Guide: Microbiology Fundamentals (Chapters 1, 3, 4, 5, 6)

Characteristics of Life

Defining Features of Living Organisms

Living organisms share several fundamental characteristics that distinguish them from non-living matter. Understanding these features is essential in microbiology.

• Cellular Organization: All living things are composed of cells, which are the basic units of life.

• Metabolism: Organisms carry out chemical reactions to obtain energy and build cellular components.

• Growth and Development: Living things grow and develop according to specific instructions coded in their DNA.

• Reproduction: Organisms reproduce to pass on genetic information to the next generation.

• Response to Stimuli: Living things respond to environmental changes.

• Homeostasis: The ability to maintain a stable internal environment.

• Evolution: Populations of organisms evolve over time through genetic changes.

Prokaryotic Cell Characteristics

Structure and Function of Prokaryotic Components

Prokaryotes, such as bacteria, have unique cellular structures that contribute to their survival and function.

• Flagella: Used for motility; whip-like appendages that propel the cell.

• Pili and Fimbriae: Hair-like structures for attachment and conjugation (transfer of genetic material).

• Periplasmic Flagella (Spirochetes): Internal flagella that allow corkscrew movement.

• Slime Layer: Protective, loosely attached layer outside the cell wall.

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

• Cell Membrane: Controls entry and exit of substances; site of metabolic activities.

• Cytoplasm: Gel-like substance containing enzymes, nutrients, and genetic material.

• Endospore: Highly resistant, dormant structure for survival in harsh conditions.

• 70S Ribosomes: Sites of protein synthesis; smaller than eukaryotic ribosomes.

• Plasmid: Small, circular DNA molecules; carry non-essential genes, often for antibiotic resistance.

• Chromosome: Main DNA molecule; contains essential genetic information.

Gram Positive vs. Gram Negative Cell Wall Structure

Comparison of Bacterial Cell Walls

Bacteria are classified based on their cell wall structure, which affects staining, susceptibility to antibiotics, and pathogenicity.

• Gram Positive: Thick peptidoglycan layer, teichoic acids, no outer membrane.

• Gram Negative: Thin peptidoglycan layer, outer membrane with lipopolysaccharide (LPS), contains endotoxin.

• Mycolic Acid: Found in cell walls of Mycobacterium species; provides resistance to chemicals and dehydration.

Feature	Gram Positive	Gram Negative
Peptidoglycan	Thick	Thin
Teichoic Acid	Present	Absent
Outer Membrane	Absent	Present
LPS (Endotoxin)	Absent	Present
Mycolic Acid	Absent	Present in Mycobacterium

Bacterial Cell Shapes and Arrangements

Classification of Bacterial Morphology

Bacteria are classified by their shapes and arrangements, which aid in identification.

• Bacillus: Rod-shaped

• Coccus: Spherical

• Spirillum: Spiral-shaped, rigid

• Spirochete: Spiral-shaped, flexible

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

Scientific Naming and Taxonomy

Binomial Nomenclature and Classification

Microorganisms are named using a standardized system and classified into hierarchical categories.

• Scientific Name: Genus (capitalized) and species (lowercase), italicized (e.g., Escherichia coli).

• Taxonomy Categories: Kingdom, Phylum, Class, Order, Family, Genus, Species.

Koch’s Postulates and Key Scientists

Foundations of Microbial Pathogenesis

Koch’s postulates are criteria for establishing a causal relationship between a microbe and a disease. Several scientists contributed to microbiology.

• Koch’s Postulates:

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

  2. Microbe must be isolated and grown in pure culture.

  3. Microbe must cause disease when introduced into a healthy host.

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

• van Leeuwenhoek: First to observe microbes with a microscope.

• Lister: Developed antiseptic techniques.

• Pasteur: Disproved spontaneous generation; developed vaccines.

• Semmelweis: Promoted handwashing to prevent disease.

Characteristics of Organic Molecules

Structure and Function in Microbiology

Organic molecules are compounds containing carbon and are essential for life.

• Carbohydrates: Energy source and structural components.

• Lipids: Membrane structure and energy storage.

• Proteins: Enzymes, structural, and regulatory functions.

• Nucleic Acids: Genetic information (DNA, RNA).

Endosymbiotic Theory

Origin of Eukaryotic Organelles

The endosymbiotic theory explains the origin of mitochondria and chloroplasts in eukaryotic cells.

• Evidence:

  • Mitochondria and chloroplasts have their own DNA, similar to prokaryotes.

  • Double membranes suggest engulfment.

  • Ribosomes are 70S, like prokaryotes.

  • Reproduce independently by binary fission.

Eukaryotic Cell Characteristics

Structure and Function of Eukaryotic Components

Eukaryotic cells are more complex than prokaryotes, with specialized organelles.

• Cilia and Flagella: Motility structures; cilia are short and numerous, flagella are long and few.

• Cell Membrane: Phospholipid bilayer; regulates transport.

• Cytoplasm: Contains organelles and cytosol.

• Nucleus: Contains DNA; site of transcription.

• 80S Ribosomes: Larger than prokaryotic ribosomes; site of protein synthesis.

• Endoplasmic Reticulum: Rough ER (protein synthesis), Smooth ER (lipid synthesis).

• Golgi Apparatus: Modifies, sorts, and packages proteins.

• Mitochondria: Site of ATP production.

• Chloroplasts: Site of photosynthesis in plants and algae.

Eukaryotic Cell Reproduction

Mechanisms of Cell Division

Eukaryotic cells reproduce by mitosis (for growth and repair) and meiosis (for sexual reproduction).

• Mitosis: Produces two genetically identical daughter cells.

• Meiosis: Produces four genetically unique gametes.

Comparison: Prokaryotic vs. Eukaryotic Cells

Key Differences

Feature	Prokaryotic	Eukaryotic
Nucleus	Absent	Present
Ribosome Size	70S	80S
Membrane-bound Organelles	Absent	Present
Cell Wall	Peptidoglycan	Cellulose, chitin, or absent
Reproduction	Binary fission	Mitosis/meiosis

Types of Eukaryotic Microbes

Fungi, Protozoans, and Helminths

Eukaryotic microbes include fungi, protozoans, and helminths, each with distinct characteristics and associated diseases.

• Fungi: Non-motile, cell walls of chitin, reproduce by spores. Example: Candida albicans causes candidiasis.

• Protozoans: Motile, no cell wall, complex life cycles. Example: Plasmodium causes malaria.

• Helminths: Multicellular worms, complex life cycles. Example: Ascaris lumbricoides causes ascariasis.

Characteristics of Viruses

Structure and Classification

Viruses are acellular entities that require a host for replication.

• Capsid: Protein shell enclosing genetic material.

• Capsomeres: Subunits of the capsid.

• Nucleic Acid Core: DNA or RNA, single or double-stranded.

• Envelope: Lipid membrane surrounding some viruses; non-enveloped viruses lack this.

Types of Genetic Material in Viruses

Viral Genome Diversity

• DNA Viruses: Can be single or double-stranded.

• RNA Viruses: Can be single or double-stranded; may be positive or negative sense.

Viral Multiplication

General Steps in Viral Replication

• Attachment

• Penetration

• Uncoating

• Replication

• Assembly

• Release

Cytopathic Effects, Transformed Cells, and Oncoviruses

Impact of Viral Infection

• Cytopathic Effects: Structural changes in host cells due to viral infection.

• Transformed Cell: Cell that has undergone changes leading to uncontrolled growth (cancer).

• Oncovirus: Virus capable of causing cancer (e.g., Human papillomavirus).

Bacteriophages and Their Life Cycle

Viruses That Infect Bacteria

• Bacteriophage: Virus that infects bacteria.

• Lytic Cycle: Virus replicates and lyses host cell.

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

Virus Cultivation

Methods for Growing Viruses

• Cell cultures

• Embryonated eggs

• Live animals

Prions, Viroids, and Satellites

Unusual Infectious Agents

• Prions: Infectious proteins causing neurodegenerative diseases (e.g., Creutzfeldt-Jakob disease).

• Viroids: Small, circular RNA molecules infecting plants.

• Satellites: Nucleic acid molecules that require a helper virus for replication.

Bacterial Classification by Oxygen Requirements

Types and Enzymes Involved

• Obligate Aerobes: Require oxygen.

• Obligate Anaerobes: Cannot tolerate oxygen.

• Facultative Anaerobes: Can grow with or without oxygen.

• Microaerophiles: Require low oxygen levels.

• Aerotolerant Anaerobes: Do not use oxygen but tolerate it.

• Enzymes: Superoxide dismutase, catalase, and peroxidase detoxify reactive oxygen species.

Bacterial Classification by Temperature Requirements

Temperature Preferences

• Psychrophiles: Grow at low temperatures (0–15°C).

• Mesophiles: Grow at moderate temperatures (20–45°C).

• Thermophiles: Grow at high temperatures (45–80°C).

• Hyperthermophiles: Grow at very high temperatures (>80°C).

Sample Discussion Questions

Practice for Exam Preparation

• Compare and contrast the gram positive and gram negative cell wall structure.

• What is the endosymbiotic theory and give the evidence for the theory.

• Discuss at least 5 important cellular organelles found in eukaryotes.

• Discuss the life cycle of a bacteriophage.

Example Answer: The gram positive cell wall is characterized by a thick peptidoglycan layer and teichoic acids, while the gram negative cell wall has a thin peptidoglycan layer, an outer membrane containing LPS, and endotoxin. Mycolic acid is present in the cell wall of Mycobacterium species.

Additional info: For exam preparation, practice writing clear, complete answers in your own words, using examples and comparisons where appropriate.