BackBIO-55 Exam 2 Study Guide: Eukaryotes, Fungi, Protists, Helminths, Viruses, Microbial Genetics, and Bacterial Growth
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Eukaryotic Cells: Origins, Structure, and Function
Origins and Organization of Eukaryotic Cells
Eukaryotic cells are complex cells with membrane-bound organelles, believed to have evolved through two main processes: endosymbiosis and membrane infolding. Their internal organization supports specialized functions and compartmentalization.
Endosymbiosis Theory: One cell engulfs another, which survives inside and forms a permanent, heritable symbiotic relationship. This explains the origin of mitochondria, chloroplasts, cilia, flagella, and centrioles.
Membrane Infolding: The cell's own membrane folds inward, creating internal compartments such as the endoplasmic reticulum (ER), lysosomes, nucleus, and Golgi apparatus.
Cell Organization: Eukaryotic cells have three main areas: external structures, the cell boundary, and the internal cytoplasm containing organelles.
External Structures & Locomotion
Flagella: Used for locomotion; thicker than prokaryotic flagella, covered by the cell membrane, and composed of microtubules in a "9+2" arrangement. Movement is whip-like or lashing. Example: Trichomonas vaginalis.
Cilia: Shorter, more numerous than flagella; used for movement, feeding, and filtering. Found in certain protozoa and animal cells.
Glycocalyx: Outermost boundary made of polysaccharides; functions in adherence, protection, and signal reception.
The Cell Boundary
Structure | Presence/Absence | Composition | Key Function |
|---|---|---|---|
Cell Wall | Present in fungi (thick, rigid) and most algae; absent in protozoa, few algae, and all animal cells | Fungi: chitin/cellulose; Algae: cellulose, pectin, mannans, silicon dioxide, calcium carbonate | Provides rigid support and shape |
Cell/Cytoplasmic Membrane | Present in all eukaryotes | Phospholipid bilayer with embedded proteins and sterols (e.g., ergosterol in fungi) | Selectively permeable barrier for transport, adhesion, secretion, and signal transduction |
Internal Organelles and the Endomembrane System
Nucleus: Double-membraned organelle with pores; contains chromosomes (DNA + histones) and nucleolus (site of rRNA synthesis and ribosome assembly).
Endomembrane System: Includes nuclear envelope, ER, and Golgi apparatus.
Rough ER (RER): Studded with ribosomes; synthesizes proteins for secretion.
Smooth ER (SER): Lacks ribosomes; synthesizes and stores lipids, processes nutrients.
Golgi Apparatus: Stack of cisternae; modifies, stores, and packages proteins/lipids from ER.
Ribosomes: Sites of protein synthesis; larger than prokaryotic ribosomes; found free or attached to RER.
Vesicles:
Lysosomes: Contain digestive enzymes; involved in intracellular digestion and defense.
Vacuoles: Membrane-bound sacs for storage, digestion, or excretion.
Energy-Converting Organelles and Cytoskeleton
Mitochondria: Site of ATP production via aerobic respiration; inner membrane forms cristae; contains its own DNA and ribosomes (evidence for endosymbiosis); divides independently.
Chloroplasts: Site of photosynthesis in algae and plants; inner membrane forms thylakoids (stacked into grana).
Cytoskeleton: Network of microfilaments and microtubules; provides structure, anchors organelles, and enables movement.
The Kingdom Fungi
General Characteristics and Forms
Cell Structure: Cell wall made of chitin; membrane contains ergosterol.
Growth Forms:
Yeast: Unicellular, round/oval, reproduce by budding; chains of buds form pseudohyphae.
Molds (Filamentous Fungi): Multicellular, composed of hyphae (threadlike cells); a mass of hyphae is a mycelium.
Dimorphic Fungi: Can exist as yeast or mold depending on environment; pathogenic fungi are often yeast in tissues.
Hyphae Types: Septate (with cross-walls) or non-septate (continuous); vegetative (nutrient absorption) or reproductive (spore production).
Reproduction and Classification
Asexual Reproduction: By fragmentation or spores (mitosis).
Sporangiospores: Formed inside a sac (sporangium).
Conidia: Free spores, not enclosed.
Sexual Reproduction: Fusion of different hyphae strains; basis for classification.
Phylum | Sexual Spore Type | Example |
|---|---|---|
Zygomycota | Zygospores | Bread mold |
Ascomycota (Sac Fungi) | Ascospores (in ascus) | Yeasts, truffles, morels |
Basidiomycota (Club Fungi) | Basidiospores (on basidium) | Mushrooms, toadstools |
Imperfect Fungi (Deuteromycetes) | N/A (only asexual observed) | N/A |
Fungal Impacts and Infections (Mycoses)
Adverse Impacts: Mycoses (infections), allergies, toxin production (e.g., aflatoxin), crop/food destruction.
Beneficial Impacts: Decomposers, antibiotic sources, production of alcohol, acids, and food.
Mycoses Categories:
Superficial/Cutaneous: Affect skin, hair, nails; e.g., athlete's foot (tinea pedis), yeast infections (Candida albicans).
Systemic: Deep infections, often inhaled as spores; e.g., histoplasmosis (Histoplasma capsulatum), coccidioidomycosis (Coccidioides immitis).
Fungal Intoxications: Disease from mycotoxins, not infection; e.g., ergot poisoning (Claviceps purpurea), aflatoxin (Aspergillus flavus), ethanol (Saccharomyces cerevisiae).
The Protists
General Characteristics
Algae: Photosynthetic eukaryotes with chlorophyll a; unicellular or colonial; base of aquatic food webs; some (dinoflagellates) cause red tides and release toxins.
Protozoa: Unicellular, heterotrophic eukaryotes; lack tissues; feed by engulfing food; mostly free-living in moist environments.
Protozoan Structure: No cell wall; cytoplasm divided into ectoplasm (outer, for movement/feeding/protection) and endoplasm (inner, contains nucleus, mitochondria, vacuoles).
Protozoan Life Cycle and Classification
Stage | Description | Function in Disease |
|---|---|---|
Trophozoite | Motile, feeding stage; requires food and moisture | Active, damaging form in host |
Cyst | Dormant, protective stage; forms in harsh conditions | Resistant to heat, drying, chemicals; aids transmission |
Transmission: Cyst-formers (e.g., Entamoeba histolytica, Giardia lamblia) spread via contaminated food/water; non-cyst-formers (e.g., Trichomonas vaginalis) require direct contact.
Group | Motility | Pathogen Examples |
|---|---|---|
Mastigophora (Flagellates) | Flagella (or flagella + amoeboid) | Giardia lamblia, Trichomonas vaginalis, Trypanosoma brucei, T. cruzi |
Sarcodina (Amoebas) | Pseudopods | Entamoeba histolytica |
Ciliophora (Ciliates) | Cilia | Balantidium |
Apicomplexa (Sporozoa) | Non-motile (mostly) | Plasmodium, Toxoplasma gondii, Cryptosporidium |
The Parasitic Helminths
General Features and Classification
Definition: Multicellular animals (tapeworms, flukes, roundworms) with organs for reproduction, digestion, movement; often have hooks/suckers for attachment.
Group | Key Characteristics | Subgroups/Examples |
|---|---|---|
Flatworms (Platyhelminthes) | Flat body, simple nervous system, mostly hermaphroditic, absorb nutrients directly | Cestodes (tapeworms): Taenia saginata; Trematodes (flukes): Schistosoma |
Roundworms (Nematodes) | Round body, complete digestive tract, protective cuticle, sexes separate | Ascaris lumbricoides, Enterobius vermicularis, Necator americanus |
Life Cycle: Egg, larva, adult stages; definitive host (adult matures, sexual reproduction), intermediate host (larval development); infection via contaminated food/water/soil or skin penetration.
Viruses
General Properties and Structure
Definition: Obligate intracellular parasites; infect all life forms; not cellular; ultramicroscopic (20–450 nm).
Genome: DNA or RNA (never both).
Structure: Covering (capsid, sometimes envelope) and core (nucleic acid, sometimes enzymes).
Capsid: Protein shell made of capsomers.
Nucleocapsid: Capsid + nucleic acid.
Envelope: Lipid covering (mainly in animal viruses), acquired from host; spikes for attachment.
Genome Types: +ssRNA (ready for translation), -ssRNA (must be converted), dsDNA, etc.
Pre-formed Enzymes: Polymerases, replicases, reverse transcriptase (e.g., HIV).
Capsid Types: Helical (cylindrical), icosahedral (20-sided), complex (e.g., poxviruses, bacteriophages).
Viral Classification and Multiplication
Baltimore Classification: Seven classes based on nucleic acid type, strandedness, and replication method.
ICTV Taxonomy: Family names end in -viridae; genus names end in -virus.
Animal Virus Multiplication (Six Phases):
Adsorption: Virus binds to specific host receptors (spikes or capsid); tropism = tissue specificity.
Penetration: Entry by fusion (enveloped) or endocytosis (engulfed in vesicle).
Uncoating: Release of viral genome from capsid.
Synthesis: Viral components produced (DNA viruses in nucleus, RNA viruses in cytoplasm).
Assembly: New virions constructed; capsid forms first.
Release: Budding/exocytosis (enveloped, gradual), or cell lysis (nonenveloped, sudden).
Viral Damage and Bacteriophages
Cytopathic Effects (CPE): Microscopic changes in host cells (e.g., syncytium formation).
Persistence: Chronic latent infections (e.g., herpes); oncoviruses cause cancer (e.g., papillomavirus, Epstein-Barr virus).
Bacteriophages: Infect bacteria; lytic cycle (host lysis), lysogeny (prophage integrates into host genome, can cause lysogenic conversion).
Nonviral Infectious Agents: Prions (misfolded proteins, cause TSEs), viroids (RNA, plant pathogens), satellite viruses (require helper virus).
Microbial Genetics
Fundamentals of Genetics and DNA Structure
Genetics: Study of heredity, gene transmission, expression, and variation.
Genome: Total genetic material (DNA) in a cell.
Gene: Sequence of nucleotides coding for a product.
Genotype: All genes present; Phenotype: Observable traits from gene expression.
Genome Location: Bacteria: single circular chromosome; Eukaryotes: multiple linear chromosomes; Viruses: DNA or RNA, few genes.
DNA Structure: Nucleotide = deoxyribose sugar + phosphate + nitrogenous base (A, T, G, C); antiparallel double helix; A-T (2 H-bonds), G-C (3 H-bonds).
DNA Replication
Semiconservative: Each new DNA has one old and one new strand.
Direction: New strand synthesized 5' to 3'.
Leading strand: Continuous synthesis.
Lagging strand: Discontinuous, forms Okazaki fragments.
Enzyme | Function |
|---|---|
Helicase | Unwinds and unzips DNA at origin |
Primase | Synthesizes RNA primer |
DNA Polymerase III | Adds bases (5'→3'), proofreads |
DNA Polymerase I | Removes primers, fills gaps, repairs |
Ligase | Joins DNA fragments |
Gyrase | Supercoils DNA |
Gene Expression: The Central Dogma
Transcription (DNA \to RNA): RNA polymerase binds promoter, synthesizes RNA using DNA template; base pairing: G-C, A-U (U replaces T in RNA).
Eukaryotic mRNA Processing: Splicing (removal of introns), capping, poly-A tail; not in prokaryotes.
RNA Type | Function | Message in Codons? |
|---|---|---|
mRNA | Conveys DNA code to ribosomes | Yes |
tRNA | Brings amino acids, has anticodon | No |
rRNA | Structural/catalytic part of ribosome | No |
Translation (RNA \to Protein): Ribosomes read mRNA codons (3 bases = 1 amino acid); start codon: AUG (methionine); stop codons: UAA, UGA, UAG; peptide bonds formed; elongation via tRNA entry and translocation.
Gene Regulation (Operons) and Mutation
Operons: Coordinated gene regulation in prokaryotes.
Inducible (catabolic): Normally OFF, turned ON by substrate (e.g., lactose operon).
Repressible (anabolic): Normally ON, turned OFF by product (e.g., arginine operon).
Mutations: Change in genotype/phenotype; spontaneous (random errors) or induced (mutagens).
Type | Description | Consequence |
|---|---|---|
Missense | Single amino acid change | Alters protein (e.g., sickle-cell anemia) |
Nonsense | Codon becomes STOP | Premature translation termination |
Frameshift | Insertion/deletion shifts reading frame | Changes entire amino acid sequence |
Genetic Recombination (Horizontal Gene Transfer)
Conjugation: Direct transfer via pilus; plasmid or chromosomal DNA.
Transformation: Uptake of free DNA from environment.
Transduction: Bacteriophage transfers DNA; generalized (random) or specialized (specific genes).
Bacterial Growth & Reproduction
Binary Fission and Exponential Growth
Binary Fission: Asexual reproduction; one cell divides into two identical daughter cells.
Replication & enlargement
Chromosome separation & septum formation
Septum completion
Cell separation
Exponential Growth: Population doubles each generation under ideal conditions (e.g., E. coli divides every 20 min).
Mathematical Representation:
Final number of cells ():
= initial number of cells; = number of generations
Growth Curves: Arithmetic scale: J-shaped; logarithmic scale: straight line (slope = generation time).
Additional info: This guide covers key concepts in eukaryotic cell structure, fungi, protists, helminths, viruses, microbial genetics, and bacterial growth, providing definitions, examples, and tables for comparison and classification. Equations are provided in LaTeX format for clarity.
