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.

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

• Metabolism: Organisms carry out chemical reactions to obtain and use energy.

• 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 stable internal conditions.

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

Prokaryotic Cell Characteristics

Structure and Function of Prokaryotic Components

Prokaryotic cells, such as bacteria, possess unique structures that contribute to their survival and function.

• Flagella: Motility structures that allow movement.

• Pili and Fimbriae: Surface appendages for attachment and conjugation.

• Periplasmic Flagella (Spirochetes): Internal flagella that enable corkscrew motion.

• Slime Layer: Protective, loosely attached layer aiding in adherence.

• Cell Wall: Provides structural support; composition varies (see Gram staining below).

• Cell Membrane: Regulates transport of substances in and out of the cell.

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

• Endospore: Dormant, resistant structure for survival under harsh conditions.

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

• Plasmid: Small, circular DNA molecules carrying non-essential genes.

• Chromosome: Main DNA molecule containing essential genetic information.

Gram Positive vs. Gram Negative Cell Wall Structure

Comparison of Bacterial Cell Walls

Bacterial cell walls are classified as Gram positive or Gram negative based on their structure and staining properties.

Feature	Gram Positive	Gram Negative
Peptidoglycan	Thick layer	Thin layer
Teichoic Acid	Present	Absent
LPS (Lipopolysaccharide)	Absent	Present (outer membrane)
Endotoxin	Absent	Present (LPS component)
Mycolic Acid	Present in Mycobacterium	Absent

Example: Staphylococcus aureus is Gram positive; Escherichia coli is Gram negative.

Bacterial Cell Shapes and Arrangements

Classification of Bacteria by Morphology

Bacteria are classified by their shapes and arrangements.

• 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

Scientific names use binomial nomenclature: Genus (capitalized) and species (lowercase), both italicized.

• Example: Escherichia coli

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

Key Scientists and Koch’s Postulates

Contributions to Microbiology

• 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.

• Koch’s Postulates: Criteria to establish a causal relationship between a microbe and a disease:

  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.

Characteristics of Organic Molecules

Structure and Function

Organic molecules contain carbon and are essential for life.

• Carbohydrates: Energy source and structural component.

• Lipids: Energy storage, membrane structure.

• Proteins: Enzymes, structural, transport, signaling.

• 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

• Cilia and Flagella: Motility structures.

• Cell Membrane: Selective barrier.

• Cytoplasm: Contains organelles.

• Nucleus: Contains genetic material.

• 80S Ribosomes: Protein synthesis.

• Endoplasmic Reticulum: Protein and lipid synthesis.

• Golgi Apparatus: Modifies and packages proteins.

• Mitochondria: Energy production.

• Chloroplasts: Photosynthesis (in plants and algae).

Eukaryotic Cell Reproduction

Mechanisms of Cell Division

• Mitosis: Produces identical daughter cells.

• Meiosis: Produces gametes with half the chromosome number.

Comparison: Prokaryotic vs. Eukaryotic Cells

Key Differences

Feature	Prokaryotic	Eukaryotic
Nucleus	Absent	Present
Membrane-bound Organelles	Absent	Present
Ribosome Size	70S	80S
Cell Wall	Peptidoglycan	Varies (cellulose, chitin, none)
Reproduction	Binary fission	Mitosis/meiosis

Types of Eukaryotic Microbes

Fungi, Protozoans, and Helminths

• Fungi: Non-photosynthetic, cell wall of chitin; examples: Candida (yeast infections), Aspergillus (lung infections).

• Protozoans: Unicellular, motile; examples: Plasmodium (malaria), Giardia (intestinal infection).

• Helminths: Parasitic worms; examples: Ascaris (roundworm), Schistosoma (blood fluke).

Characteristics of Viruses

Structure and Types

• Capsid: Protein shell.

• Capsomeres: Subunits of capsid.

• Nucleic Acid Core: DNA or RNA.

• Envelope: Lipid membrane (enveloped viruses); absent in non-enveloped viruses.

Types of Genetic Material in Viruses

Classification by Genome

• DNA Viruses: Single or double-stranded DNA.

• RNA Viruses: Single or double-stranded RNA.

Viral Multiplication

General Steps in Viral Replication

• Attachment

• Penetration

• Uncoating

• Synthesis

• Assembly

• Release

Cytopathic Effects, Transformed Cells, and Oncoviruses

Effects of Viral Infection

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

• Transformed Cell: Cell altered to divide uncontrollably (may lead to cancer).

• Oncovirus: Virus that can cause cancer (e.g., HPV).

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., mad cow disease).

• Viroids: Small, circular RNA molecules infecting plants.

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

Classification of Bacteria 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: Tolerate oxygen but do not use it.

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

• Superoxide Dismutase: Converts superoxide radicals to hydrogen peroxide.

• Catalase: Converts hydrogen peroxide to water and oxygen.

• Peroxidase: Converts hydrogen peroxide to water.

Classification of Bacteria by Temperature Requirements

Temperature Preferences

• Psychrophiles: Grow at low temperatures (0–20°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

Examples 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.

Additional info: For each discussion question, provide clear, descriptive answers in your own words, referencing the above content.