Microbiology Study Guide: Chapters 1, 3, 4, and 6

Chapter 1: Introduction to Microbiology

Definition and Importance of Microbiology

• Microbiology is the study of organisms too small to be seen without magnification (the unaided eye).

• Microorganisms play essential roles in human health, agriculture, food production, biotechnology, and environmental recycling.

Types of Microorganisms

• Bacteria and Archaea: Prokaryotic, unicellular, lack a nucleus. Bacterial cell walls contain peptidoglycan; archaeal cell walls contain pseudopeptidoglycan. Reproduce by binary fission. Examples: Escherichia coli, Staphylococcus aureus.

• Viruses: Acellular, contain DNA or RNA (never both), obligate intracellular parasites, replicate only inside host cells. Examples: Influenza virus, HIV, Coronavirus.

• Fungi: Eukaryotic, cell walls contain chitin, absorb nutrients, reproduce via sexual and asexual spores, decomposers, not photosynthetic. Examples: Candida albicans, Aspergillus.

• Protozoa: Unicellular eukaryotes, no cell wall, often motile (flagella, cilia, pseudopodia), live in aqueous environments. Examples: Giardia, Plasmodium.

• Algae: Photosynthetic eukaryotes, produce oxygen, cell walls often contain cellulose.

• Helminths: Parasitic worms, multicellular eukaryotes, microscopic eggs and larvae. Examples: Tapeworms, Roundworms.

• Prions: Infectious proteins, no DNA or RNA, cause fatal neurodegenerative diseases. Examples: Mad Cow Disease, Creutzfeldt-Jakob Disease.

Historical Contributors to Microbiology

Scientist	Contribution
Antonie van Leeuwenhoek	First observed microorganisms
Francesco Redi	Challenged spontaneous generation
John Needham	Supported spontaneous generation
Lazzaro Spallanzani	Improved experimental controls
Louis Pasteur	Swan-neck flask experiment; disproved spontaneous generation
Robert Koch	Koch's Postulates
Joseph Lister	Antiseptic surgery
Ignaz Semmelweis	Handwashing
Florence Nightingale	Sanitation and nursing
Edward Jenner	Smallpox vaccine
John Snow	Epidemiology
Hans Christian Gram	Gram stain
Carolus Linnaeus	Taxonomy

Pasteur's Swan-Neck Flask Experiment

• Hypothesis: Microorganisms arise from existing microorganisms (biogenesis).

• Results: Broth remained sterile when dust could not enter; growth occurred when flask neck was broken.

• Conclusion: Spontaneous generation is false.

• Significance: Established the principle of biogenesis.

Koch's Postulates

1. Microorganism must be present in all diseased individuals.

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

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

4. Same organism must be recovered from newly infected host.

Three Domains of Life

Domain	Cell Type
Bacteria	Prokaryotic
Archaea	Prokaryotic
Eukarya	Eukaryotic

Taxonomic Hierarchy

• Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species

• Mnemonic: Dear King Philip Came Over For Good Soup

Binomial Nomenclature Rules

• Genus capitalized, species lowercase

• Italicized when typed (Escherichia coli), underlined when handwritten

Prokaryotic vs. Eukaryotic Cells

Feature	Prokaryotic	Eukaryotic
Nucleus	No	Yes
Organelles	No	Yes
DNA	Circular	Linear
Ribosomes	70S	80S
Size	Smaller	Larger

Chapter 3: Prokaryotic Cell Structure and Function

General Characteristics

• Prokaryotic cells lack a nucleus and membrane-bound organelles.

• Contain circular DNA and divide by binary fission.

• Examples: Bacteria and Archaea.

Cell Envelope

• Consists of glycocalyx (if present), cell wall, and plasma membrane.

• Functions: Protection, shape, regulation of transport.

Gram-Positive vs. Gram-Negative Bacteria

Feature	Gram-Positive	Gram-Negative
Peptidoglycan Layer	Thick	Thin
Teichoic Acids	Present	Absent
Outer Membrane	Absent	Present
LPS	Absent	Present
Stain	Purple	Pink
Examples	Staphylococcus, Streptococcus	E. coli, Salmonella

Lipopolysaccharide (LPS)

• Components: Lipid A (endotoxin, toxic), core polysaccharide, O antigen.

• Effects: Fever, inflammation, septic shock.

Acid-Fast Bacteria

• High mycolic acid content, waxy cell wall, difficult to stain.

• Example: Mycobacterium tuberculosis.

Prokaryotic Cell Morphologies and Arrangements

• Shapes: Cocci, Bacilli, Coccobacilli, Vibrios, Spirilla, Spirochetes, Pleomorphic.

• Arrangements: Diplococci, Streptococci, Staphylococci, Tetrads, Sarcinae.

Flagellar Arrangements

Arrangement	Description
Monotrichous	One flagellum
Lophotrichous	Tuft at one pole
Amphitrichous	One or more at both poles
Peritrichous	Flagella all over cell

Motility Structures

• Flagella: Motility

• Axial filaments (endoflagella): Found in spirochetes

• Cilia: Rare in prokaryotes, common in eukaryotes

• Pseudopodia: Used by some eukaryotic cells

Plasma Membrane Functions

• Selective permeability

• Energy production

• Transport

• Cell wall synthesis

Transport Mechanisms

• Passive Transport (No ATP):

  • Simple Diffusion: High → Low concentration, no proteins (e.g., O2 entry)

  • Facilitated Diffusion: High → Low, requires channel/carrier proteins (e.g., glucose transport)

  • Osmosis: Diffusion of water, moves from hypotonic to hypertonic solution

• Active Transport (ATP Required):

  • Active Transport: Low → High concentration, uses ATP

  • Group Translocation: Unique to prokaryotes, substance chemically altered during transport (e.g., glucose phosphorylation)

  • Endocytosis (eukaryotes only): Phagocytosis, pinocytosis, receptor-mediated endocytosis

  • Exocytosis: Vesicles fuse with membrane, contents released outside cell

Internal Structures

• Nucleoid: Contains bacterial chromosome; no membrane.

• Plasmid: Small, circular, extrachromosomal DNA; often carries antibiotic resistance genes.

• Ribosomes: 70S, site of protein synthesis.

• Inclusion Bodies: Nutrient storage.

• Endospores: Survival structures (e.g., Bacillus, Clostridium).

External Structures

• Glycocalyx: Capsule (organized, virulence factor) or slime layer (loose, associated with biofilms).

• Fimbriae: Adhesion to surfaces and biofilm formation.

• Pili: Attachment, conjugation (DNA transfer), and movement.

• Flagella: Motility.

Chapter 4: Eukaryotic Cell Structure and Function

General Characteristics

• Eukaryotic cells have a true nucleus, membrane-bound organelles, linear chromosomes, and 80S ribosomes.

• Divide by mitosis and meiosis.

Major Groups of Eukaryotic Microbes

• Fungi: Chitin cell walls, includes yeasts and molds.

• Protozoa: Unicellular, motile.

• Algae: Photosynthetic.

• Helminths: Parasitic worms.

Major Organelles and Functions

Organelle	Function
Nucleus	DNA storage
Ribosomes	Protein synthesis
Rough ER	Protein production
Smooth ER	Lipid synthesis
Golgi Apparatus	Packaging and secretion
Mitochondria	ATP production
Lysosomes	Digestion
Cytoskeleton	Shape and movement

Cell Cycle Overview

• Interphase: G1 (growth), S (DNA replication), G2 (preparation for division)

Cell Division

• Mitosis: Produces 2 identical diploid cells for growth, repair, and asexual reproduction.

• Meiosis: Produces 4 genetically unique haploid cells for sexual reproduction and genetic diversity.

Mitosis Stages

• Prophase: Chromosomes condense, spindle forms

• Metaphase: Chromosomes align at center

• Anaphase: Sister chromatids separate

• Telophase: Nuclear envelopes reform

• Cytokinesis: Cell splits

Meiosis Unique Features

• Synapsis: Homologous chromosomes pair

• Crossing Over: Exchange of genetic material

• Independent Assortment: Random chromosome alignment

Chapter 6: Viruses, Viroids, and Prions

Viruses: Structure and Classification

• Viruses are infectious, acellular agents containing DNA or RNA (never both).

• Nonliving: Cannot reproduce or carry out metabolism independently.

• Compared to cells: Lack cellular structure, metabolism, and independent replication.

• Viral Structures: Capsid (protein coat), envelope (lipid membrane in some viruses), spikes (attachment proteins).

• Virion: Complete infectious viral particle.

• Nucleocapsid: Capsid plus nucleic acid.

• Genome Types: DNA or RNA; single- or double-stranded.

• Classification: By shape, genome type, envelope presence, and replication cycle.

• Retroviruses: RNA viruses with reverse transcriptase (e.g., HIV).

Viroids

• Small, circular RNA molecules with no protein coat.

• Infect plants, causing diseases that affect growth and crop yield.

• Simpler than viruses; lack capsid and envelope.

Prions

• Infectious misfolded proteins; lack DNA or RNA.

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

• Induce misfolding of normal proteins.

Viral Replication Cycles

Bacteriophage Replication

• Lytic Cycle: Attachment → Penetration → Biosynthesis → Assembly → Release (lysis). Host cell dies; rapid viral replication.

• Lysogenic Cycle: Viral DNA integrates into host genome (prophage); no immediate host cell death; can switch to lytic cycle later.

• Benefits of Lysogeny: Long-term survival, genome replication with host, avoids immune detection.

Animal Virus Replication vs. Bacteriophage Replication

Feature	Bacteriophages	Animal Viruses
Host	Bacteria	Eukaryotic cells
Entry	Inject nucleic acid	Endocytosis, direct penetration, or membrane fusion
Uncoating	Not required	Capsid must be uncoated
Release	Cell lysis	Budding (enveloped) or lysis (naked)

Proto-Oncogenes vs. Oncogenes

• Proto-oncogenes: Normal genes regulating cell growth, division, and survival.

• Oncogenes: Mutated or overexpressed proto-oncogenes causing uncontrolled cell division (cancer).

• Mutations: Point mutations, gene amplification, chromosomal translocations.

Feature	Proto-Oncogene	Oncogene
Status	Normal	Mutated/overexpressed
Function	Regulates normal growth	Drives uncontrolled growth
Role in Cancer	No	Yes
Mutation Effect	None	Gain of function

Neoplasms: Benign vs. Malignant

• Neoplasm: Abnormal mass of tissue from uncontrolled cell division.

• Benign: Slow growth, well-defined borders, no invasion/metastasis, cells resemble normal tissue.

• Malignant: Rapid growth, poorly defined borders, invades/metastasizes, abnormal cells, cancerous.

Feature	Benign	Malignant
Growth Rate	Slow	Rapid
Cell Appearance	Normal	Abnormal
Invasion	No	Yes
Metastasis	No	Yes
Cancerous	No	Yes

Viral Shapes

• Helical: e.g., Tobacco mosaic virus

• Polyhedral (Icosahedral): e.g., Adenovirus

• Enveloped: e.g., Influenza virus, HIV

• Complex: e.g., Bacteriophages

Lytic vs. Lysogenic Cycles

Step	Lytic Cycle	Lysogenic Cycle
1	Attachment	Attachment
2	Penetration	Penetration
3	Biosynthesis	Integration into host DNA
4	Assembly	Host cell reproduces
5	Release (lysis)	Induction → enters lytic cycle
Outcome	Host cell dies, rapid replication	Host survives initially, viral DNA replicated with host

Key Terms

Term	Definition
Virulent Phage	Uses lytic cycle
Temperate Phage	Uses lysogenic cycle
Prophage	Viral DNA integrated into bacterial chromosome
Provirus	Viral DNA integrated into animal chromosome
Lysogenic Conversion	Host gains new traits from prophage

Important Viral Families and Clinical Viruses

Orthomyxoviridae (Influenza Viruses)

• Enveloped, helical capsid, single-stranded RNA (-), segmented genome, replicates partly in nucleus.

• Diseases: Seasonal influenza, pandemics.

• Surface glycoproteins: Hemagglutinin (HA) for attachment, Neuraminidase (NA) for viral release.

Type	Infects	Significance
Influenza A	Humans and animals	Pandemics
Influenza B	Humans only	Seasonal epidemics
Influenza C	Humans	Mild disease
Influenza D	Cattle	Not a major human pathogen

Antigenic Drift vs. Antigenic Shift

Feature	Drift	Shift
Change	Minor	Major
Cause	Point mutation	Reassortment
Speed	Gradual	Sudden
Influenza A	Yes	Yes
Influenza B	Yes	No
Pandemic Potential	Low	High

Retroviridae (HIV)

• Enveloped, single-stranded RNA (+), diploid genome, reverse transcriptase.

• Unique enzymes: Reverse transcriptase (RNA → DNA), integrase, protease.

• Targets CD4+ T cells, macrophages, dendritic cells.

• Uses CD4 receptor and CCR5/CXCR4 co-receptors.

• Progression: HIV infection → CD4 destruction → Immunodeficiency → AIDS.

Herpesviridae

• Enveloped, double-stranded DNA, icosahedral capsid, establish latent infections.

• Major viruses: HSV-1 (oral herpes), HSV-2 (genital herpes), VZV (chickenpox, shingles), EBV (mononucleosis), CMV (congenital infections), HHV-6 (roseola), HHV-8 (Kaposi sarcoma).

• Latency: Virus remains dormant and may reactivate (e.g., HSV in sensory ganglia).

Papillomaviridae (HPV)

• Non-enveloped, double-stranded DNA, icosahedral capsid.

• Low-risk types (HPV 6, 11): Genital warts.

• High-risk types (HPV 16, 18): Cervical, anal, oropharyngeal cancer.

Cancer-Causing Viruses

Virus	Cancer Association
HPV 16/18	Cervical cancer
EBV	Burkitt lymphoma
HBV	Liver cancer
HCV	Liver cancer
HHV-8	Kaposi sarcoma

Key Exam Tips

• Proto-oncogene → oncogene = uncontrolled growth

• Malignant neoplasm = cancer

• Benign ≠ harmless, but malignant = dangerous

Additional info: For diagrams (e.g., cell morphologies, viral replication cycles), refer to textbook figures for visual reinforcement. For fill-in-the-blank and structure identification, focus on recognizing key features described above.