Microbiology Exam 1 Study Guide: Cell Structure, Microbial Diversity, and Viruses

Introduction to Microbiology

Definition, Scope, and Importance

Microbiology is the study of microscopic organisms, including bacteria, archaea, fungi, protozoa, algae, and viruses. It is a foundational science that impacts medicine, ecology, industry, and biotechnology.

• Microorganisms are essential for nutrient cycling, decomposition, and maintaining ecological balance.

• They play critical roles in human health, both as pathogens and as beneficial members of the normal microbiota.

• Applications include food production, pharmaceuticals, and environmental remediation.

• Example: Lactobacillus species are used in yogurt production.

Major Groups of Microorganisms

Bacteria, Archaea, Fungi, Protozoa, Algae, and Viruses

• Bacteria: Prokaryotic, diverse shapes, found in many environments.

• Archaea: Prokaryotic, often extremophiles, distinct from bacteria in cell wall composition.

• Fungi: Eukaryotic, includes yeasts and molds, decomposers.

• Protozoa: Eukaryotic, motile, often aquatic, some are pathogens.

• Algae: Eukaryotic, photosynthetic, important in aquatic ecosystems.

• Viruses: Acellular, require host cells for replication.

• Example: Escherichia coli (bacteria), Aspergillus (fungi), Plasmodium (protozoa).

Prokaryotic vs. Eukaryotic Cells

Structural and Functional Differences

• Prokaryotic cells: Lack a nucleus and membrane-bound organelles; DNA is in a nucleoid region.

• Eukaryotic cells: Have a nucleus and organelles such as mitochondria, ER, Golgi complex.

• Prokaryotes include bacteria and archaea; eukaryotes include fungi, protozoa, algae, and helminths.

• Example: Bacterial cell vs. human cell.

Historical Development of Microbiology

Key Scientists and Discoveries

• Robert Hooke: First described cells (1665).

• Antonie van Leeuwenhoek: Observed "animalcules" (microbes) with a simple microscope.

• Louis Pasteur: Disproved spontaneous generation, developed pasteurization.

• Robert Koch: Developed Koch's postulates, linking microbes to disease.

• Example: Pasteur's swan-neck flask experiment.

Disproving Spontaneous Generation

Pasteur's Experiments and Biogenesis

• Pasteur showed that life does not arise spontaneously; microbes come from other microbes.

• His experiments used swan-neck flasks to prevent contamination.

• Biogenesis: The principle that living things arise from other living things.

• Example: No microbial growth in sterile broth unless exposed to air.

Koch's Postulates

Linking Microbes to Disease

• Koch's postulates are criteria to establish a causal relationship between a microbe and a disease:

  1. The microorganism must be found in all cases of the disease.

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

  3. The cultured microbe must cause disease when introduced into a healthy host.

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

• Example: Bacillus anthracis and anthrax.

Microorganisms in Ecological Balance

Nutrient Cycling, Photosynthesis, and Decomposition

• Microbes recycle nutrients (carbon, nitrogen, sulfur).

• Photosynthetic microbes (algae, cyanobacteria) produce oxygen.

• Decomposers break down organic matter.

• Example: Nitrogen-fixing bacteria in soil.

Normal Microbiota

Importance in Human Health

• Normal microbiota are the microbes that inhabit the human body without causing disease.

• They protect against pathogens, aid digestion, and stimulate the immune system.

• Example: Gut microbiota such as Bacteroides.

Prokaryotic Cell Structures & Functions

Shapes, Arrangements, and Key Structures

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

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

• Cell wall: Provides shape and protection; composed of peptidoglycan in bacteria.

• Plasma membrane: Controls transport; composed of phospholipid bilayer.

• Ribosomes: Site of protein synthesis; 70S in prokaryotes.

• Flagella: Motility; rotates like a propeller.

• Fimbriae and pili: Attachment and conjugation.

• Example: Escherichia coli with flagella.

Gram-Positive vs. Gram-Negative Bacterial Cell Walls

Structure, Staining, and Antibiotic Implications

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

• Gram-negative: Thin peptidoglycan, outer membrane with lipopolysaccharide, stains pink.

• Gram-negative bacteria are generally more resistant to antibiotics due to the outer membrane.

• Example: Staphylococcus aureus (Gram-positive), Escherichia coli (Gram-negative).

Plasma Membrane & Transport

Structure and Transport Mechanisms

• Structure: Phospholipid bilayer with embedded proteins.

• Passive transport: Diffusion, facilitated diffusion, osmosis.

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

• Example: Glucose transport via facilitated diffusion.

• Formula: Osmosis rate can be described by $J = -D \frac{dC}{dx}$

Bacterial Motility and Chemotaxis

Flagella and Axial Filaments

• Flagella: Long, whip-like structures for movement.

• Axial filaments: Found in spirochetes, allow corkscrew motion.

• Chemotaxis: Movement toward or away from chemical stimuli.

• Example: Treponema pallidum (spirochete with axial filaments).

Endospores

Formation, Function, and Significance

• Endospores: Highly resistant, dormant structures formed by some bacteria (e.g., Bacillus, Clostridium).

• Sporulation: Formation of endospores under stress.

• Germination: Return to vegetative state when conditions improve.

• Example: Bacillus anthracis spores.

Prokaryotic vs. Eukaryotic Ribosomes

Structure and Function

• Prokaryotic ribosomes: 70S (30S + 50S subunits).

• Eukaryotic ribosomes: 80S (40S + 60S subunits).

• Both synthesize proteins, but differ in size and sensitivity to antibiotics.

• Example: Antibiotics like tetracycline target 70S ribosomes.

Eukaryotic Cell Organelles

Structure and Function

• Nucleus: Contains DNA, site of transcription.

• Endoplasmic reticulum (ER): Protein and lipid synthesis.

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

• Mitochondria: ATP production via cellular respiration.

• Chloroplasts: Photosynthesis in plants and algae.

• Lysosomes: Digestive enzymes for breakdown of macromolecules.

• Example: Mitochondria in animal cells, chloroplasts in algae.

Major Groups of Eukaryotic Microorganisms

Fungi, Algae, Protozoa, and Helminths

• Fungi: Yeasts (unicellular), molds (multicellular), reproduce sexually/asexually.

• Algae: Photosynthetic, aquatic, unicellular or multicellular.

• Protozoa: Motile, heterotrophic, complex life cycles.

• Helminths: Parasitic worms; flatworms (Platyhelminthes) and roundworms (Nematoda).

• Example: Candida albicans (fungus), Plasmodium (protozoan), Ascaris (helminth).

Fungi

Characteristics, Cell Walls, and Reproduction

• Yeasts: Unicellular, reproduce by budding.

• Molds: Multicellular, filamentous hyphae.

• Cell wall: Composed of chitin, not peptidoglycan.

• Asexual spores: Conidia, sporangiospores.

• Sexual spores: Zygospores, ascospores, basidiospores.

• Example: Aspergillus (mold), Candida albicans (yeast).

Medically Important Fungi

Diseases and Pathogens

• Candida albicans: Causes candidiasis.

• Aspergillus: Causes aspergillosis.

• Cryptococcus: Causes cryptococcosis.

• Example: Fungal infections in immunocompromised patients.

Protozoa

Motility, Reproduction, and Life Cycles

• Motility structures: Flagella, cilia, pseudopodia.

• Reproduction: Asexual (binary fission), sexual (conjugation).

• Life cycles: Often involve multiple hosts.

• Example: Plasmodium (malaria), Giardia (giardiasis).

Protozoan Pathogens

Transmission and Disease

• Giardia: Waterborne transmission.

• Plasmodium: Transmitted by mosquitoes.

• Trypanosoma: Transmitted by tsetse flies.

• Example: Malaria caused by Plasmodium.

Helminths

Flatworms vs. Roundworms and Life Cycles

• Flatworms (Platyhelminthes): Includes flukes and tapeworms.

• Roundworms (Nematoda): Includes pinworms, hookworms.

• Life cycles often involve multiple hosts and environmental stages.

• Example: Taenia (tapeworm), Ascaris (roundworm).

Arthropods as Disease Vectors

Importance in Disease Transmission

• Arthropods (e.g., mosquitoes, ticks, fleas) transmit both eukaryotic and prokaryotic pathogens.

• Example: Mosquitoes transmit malaria and dengue.

Eukaryotic Microbes in Ecosystems, Medicine, and Biotechnology

Significance and Applications

• Fungi decompose organic matter and produce antibiotics.

• Algae are primary producers in aquatic ecosystems.

• Protozoa regulate bacterial populations.

• Helminths cause significant human disease.

• Example: Penicillin from Penicillium fungus.

Viruses, Viroids, and Prions

General Properties and Differences from Living Organisms

• Viruses: Acellular, contain nucleic acid (DNA or RNA), protein coat (capsid), sometimes envelope.

• Cannot reproduce independently; require host cells.

• Viroids: Infectious RNA molecules, no protein coat.

• Prions: Infectious proteins, cause neurodegenerative diseases.

• Example: HIV (virus), scrapie (prion).

Virus Structure and Chemical Composition

Nucleic Acids, Capsids, Envelopes, and Spikes

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

• Capsid: Protein shell, composed of capsomeres.

• Envelope: Lipid membrane derived from host cell.

• Spikes: Glycoproteins for attachment to host cells.

• Example: Influenza virus with envelope and spikes.

Virus Classification

Host Range, Morphology, and Nucleic Acid Type

• Viruses are classified by:

  • Host range (bacteria, animals, plants)

  • Morphology (helical, icosahedral, complex)

  • Nucleic acid type (DNA/RNA, single-/double-stranded)

• Example: Bacteriophage (infects bacteria), herpesvirus (infects humans).

Bacteriophage Multiplication Cycles

Lytic and Lysogenic Cycles

• Lytic cycle: Virus replicates and lyses host cell.

• Lysogenic cycle: Viral DNA integrates into host genome (prophage), can later enter lytic cycle.

• Example: Lambda phage in E. coli.

Animal Virus Replication

Comparison with Bacteriophage Replication

• Animal viruses may enter cells by endocytosis or membrane fusion.

• Replication involves uncoating, synthesis, assembly, and release.

• Bacteriophages inject DNA; animal viruses often enter whole.

• Example: Influenza virus enters by membrane fusion.

Virus Cultivation and Identification

Laboratory Methods

• Viruses are grown in cell cultures, embryonated eggs, or laboratory animals.

• Identified by cytopathic effects, serology, PCR.

• Quantified by plaque assays.

• Example: Plaque assay for bacteriophage.

Types of Viral Infections

Acute, Latent, Persistent, and Slow Infections

• Acute: Rapid onset, short duration (e.g., influenza).

• Latent: Virus remains dormant, can reactivate (e.g., herpes).

• Persistent: Long-term, continuous production (e.g., hepatitis B).

• Slow: Gradual progression (e.g., HIV).

• Example: Herpes simplex virus (latent infection).

Viral Latency and Reactivation

Mechanisms and Human Diseases

• Latent viruses integrate into host genome or remain in cells.

• Reactivation triggered by stress, immunosuppression.

• Example: Herpesviruses, HIV.

Oncogenic Viruses

Viruses and Cancer

• Some viruses cause cancer by disrupting cell cycle regulation.

• Examples: Human papillomavirus (HPV), Epstein-Barr virus.

Prions

Structure and Replication

• Prions are misfolded proteins that induce misfolding in normal proteins.

• Cause neurodegenerative diseases (e.g., Creutzfeldt-Jakob disease).

• Do not contain nucleic acids.

• Example: Mad cow disease (bovine spongiform encephalopathy).

Prevention and Control of Viral Infections

Vaccination and Antiviral Drugs

• Vaccines stimulate immunity and prevent infection.

• Antiviral drugs inhibit viral replication.

• Hygiene and public health measures reduce transmission.

• Example: Influenza vaccine, antiretroviral therapy for HIV.

Table: Comparison of Prokaryotic and Eukaryotic Cells

Feature	Prokaryotic Cells	Eukaryotic Cells
Nucleus	No	Yes
Organelles	No	Yes
Ribosome Size	70S	80S
Cell Wall Composition	Peptidoglycan (bacteria)	Chitin (fungi), cellulose (plants), none (animals)
Examples	Bacteria, Archaea	Fungi, Protozoa, Algae, Helminths

Table: Types of Viral Infections

Type	Description	Example
Acute	Rapid onset, short duration	Influenza
Latent	Dormant, can reactivate	Herpes simplex virus
Persistent	Long-term, continuous production	Hepatitis B
Slow	Gradual progression	HIV

Additional info: Academic context and examples were added to expand brief learning outcomes into comprehensive study notes. Tables were inferred and constructed for clarity.