Chapter 17: Viruses

Viral Structure

Viruses are infectious agents composed of genetic material encased in a protein shell. Their structure is highly variable and adapted to their host.

• Capsid: Protein shell made of subunits called capsomeres. Capsid symmetry varies (e.g., icosahedral, helical).

• Viral Envelope: Some viruses possess a lipid envelope derived from the host cell membrane.

• Nucleic Acid: Can be DNA or RNA, single or double stranded.

• Host Range: Viruses typically infect a narrow range of hosts. For example, humans cannot contract tobacco mosaic virus, but some animal viruses (e.g., bird, swine, bat flu) can jump species.

• Obligate Intracellular Parasites: Viruses lack metabolic enzymes and must infect host cells to reproduce.

• Cell Entry Mechanisms: Viruses use specialized proteins (e.g., coronavirus spike protein) to enter host cells.

Examples: Adenovirus, tobacco mosaic virus, coronavirus, influenza virus, bacteriophage T4.

Lytic and Lysogenic Cycles (Bacteriophages)

Bacteriophages (viruses that infect bacteria) can reproduce via two main cycles:

• Lytic Cycle: Results in destruction of the host cell. Can be caused by virulent or temperate phages.

• Lysogenic Cycle: Temperate phages integrate their DNA into the host genome as a prophage. The virus can remain latent and later switch to the lytic cycle under stress.

Examples of Viral Diseases

• HIV: Causes AIDS.

• Measles virus: Causes measles.

• Influenza virus: Causes flu.

Retroviruses

Retroviruses, such as HIV, use reverse transcriptase to copy their RNA genome into DNA, which integrates into the host genome as a provirus and can remain latent.

Evolution of Viruses

• Viruses may have evolved from fragments of prokaryotic or eukaryotic genomes.

• They could be remnants of DNA or RNA that assembled into infectious agents.

Emerging Viruses

• Examples: H5N1 (avian flu), 1918 "Spanish flu", Ebola, SARS (origin of COVID-19).

Virions, Viroids, and Prions

• Virion: Complete viral particle.

• Viroids: Infectious RNA strands affecting plants; lack structural proteins.

• Prions: Misfolded proteins causing slow, hard-to-destroy brain diseases (e.g., Mad cow disease, Kuru).

Chapter 24: Bacteria and Archaea

Unique Characteristics of Bacteria

• No Membranous Nucleus: DNA is located in a nucleoid region.

• Circular DNA: Follows classic base pairing rules.

• No Membrane-Bound Organelles: Ribosomes are present but not membrane-bound.

• Ribosome Differences: Bacterial ribosomes are smaller than eukaryotic ribosomes.

• Endospores: Some bacteria form resistant spores.

• Capsules: Protective layer against harsh conditions.

• Flagella: Used for movement; structurally different from eukaryotic flagella.

History of Microbiology

• van Leeuwenhoek: First observed prokaryotes.

• Louis Pasteur & Robert Koch: Developed methods to isolate disease-causing bacteria.

• Koch's Postulates: Criteria to establish a causative relationship between a microbe and a disease.

Bacteria vs. Archaea

• Separated based on unique biochemistry and evolutionary lineage.

• Some archaeans share genetic similarities with eukaryotes.

Prokaryotic Shapes

• Coccus: Spherical

• Bacillus: Rod-shaped

• Spirillum: Spiral-shaped

Cell Wall Differences and Gram Stain

• Peptidoglycan: Location and structure varies.

• Gram Positive: Thick peptidoglycan layer; stains violet.

• Gram Negative: Thin peptidoglycan layer; stains red.

Genetic Variation and Evolution

• Rapid reproduction and mutation rates.

• Genetic Recombination: Transformation (uptake of DNA), transduction (virus-mediated), conjugation (plasmid transfer).

• Plasmids: Small, circular DNA; can confer antibiotic resistance (e.g., F factor, R plasmids).

Nutrition and Metabolism

• Obligate Aerobes: Require oxygen.

• Obligate Anaerobes: Cannot tolerate oxygen.

• Anaerobic Respiration: Use other electron acceptors.

• Nitrogen Fixation: Conversion of atmospheric N2 to ammonia.

• Metabolic Cooperation: Heterocysts (e.g., Anabaena), biofilms.

Bacterial Lineages

• Proteobacteria: All Gram negative; subdivided into alpha, beta, gamma, delta, epsilon groups.

• Chlamydia: Gram negative; causes blindness and urethritis (Chlamydia trachomatis).

• Spirochetes: Gram negative; includes Treponema pallidum (syphilis), Borrelia burgdorferi (Lyme disease).

• Cyanobacteria: Photosynthetic; solitary or filamentous.

• Gram Positive Bacteria: Includes Clostridium botulinum, Bacillus anthracis, Staphylococcus aureus, Streptococcus pneumoniae.

• Actinomycetes: Important in soils.

Archaea

• Extreme Halophiles: Live in high salt concentrations.

• Extreme Thermophiles: Live in high temperatures.

Chapter 25: Diversification of Eukaryotes

Protists

Protists are a diverse group of eukaryotes, often considered a catch-all category for organisms that are not plants, animals, or fungi.

• Eukaryotic Features: Possess nuclei and organelles.

• Endosymbiotic Hypothesis: Early protists incorporated bacteria as mitochondria and plastids (chloroplasts), leading to serial endosymbiosis.

• Multicellularity: Evolved multiple times (e.g., Chlamydomonas to Volvox, choanoflagellates as animal ancestors).

• Special Characteristics: Single-celled, colonial, or multicellular (e.g., kelps).

• Life Cycles: Most are free-living; some are parasitic. Reproduction can be asexual or sexual.

• Nutrition: Photoautotrophic (phytoplankton), symbiotic (lichens), or heterotrophic.

• Locomotion: Cilia, pseudopodia, flagella (eukaryotic structure).

Major Protist Groups

• Excavata: Includes diplomonads (mitosomes), parabasalids (hydrogenosomes), euglenozoans (kinetoplast).

• Archaeplastida: Red algae, green algae, and plants; red algae have phycoerythrin pigment.

• SAR: Stramenopiles (diatoms, brown algae), alveolates (Plasmodium), rhizarians (amoebas).

• Unikonta: Amoebas, fungi, animals.

Algae Types

• Green Algae (Chlorophyta): Chlamydomonas, Ulva, Volvox; cellulose cell walls, chlorophyll a and b, starch storage.

• Red Algae (Rhodophyta): Used in agar, cosmetics, sushi; red pigments.

• Brown Algae (Phaeophyta): Multicellular seaweed; fucoxanthin pigment, laminarin storage.

• Diatoms: Silica shells; major component of phytoplankton.

Protist Locomotion

• Cilia: Paramecium

• Pseudopodia: Amoeboid movement

• Flagella: Eukaryotic structure

Human Diseases Caused by Protists

• Giardia lamblia: Diarrhea

• Trypanosoma brucei: Sleeping sickness (Tsetse fly)

• Trypanosoma cruzi: Chagas disease (kissing bug)

• Trichomonas vaginalis: STD

• Entamoeba histolytica: Amoebic dysentery

Other Notable Protist Features

• Red Tides: Caused by dinoflagellates; can be toxic and cause bioluminescence.

• Conjugation: Paramecium uses conjugation for genetic exchange.

• Alternation of Generations: Seen in algae; plants also exhibit this life cycle.

• Slime Molds: Plasmodial (multinucleate mass) vs. cellular (individual amoebas aggregate).

Chapter 28: Colonization of Land

Fungi

Fungi are heterotrophic eukaryotes with unique structural and reproductive features.

• Heterotrophy: Cannot photosynthesize; absorb nutrients via external digestion.

• Cell Walls: Composed of chitin, not cellulose.

• Hyphae: Filamentous structures woven into a mycelium.

• Coenocytic vs. Septate: Coenocytic lack septa; septate have cross-walls.

• Specialized Hyphae: Haustoria (parasitic), mycorrhizae (mutualistic with plants).

• Reproduction: Sexual and asexual; plasmogamy (fusion of cytoplasm), karyogamy (fusion of nuclei).

• Microsporidia: Primitive, single-celled fungi.

• Ecological Roles: Decomposers, mutualists, pathogens.

• Edible Fungi: Morels, truffles, mushrooms; yeasts used in fermentation.

Fungal Groups

• Cryptomycetes: Parasites of other fungi.

• Microsporidians: Parasites with harpoon-like spores.

• Chytrids: Attack amphibians.

• Zoopagomycetes: Animal symbionts/parasites.

• Mucuromycetes: Food storage molds.

• Ascomycetes: Sac fungi; produce ascocarps.

• Basidiomycetes: Club fungi; decomposers and mushrooms.

Seedless Plants

Early plants adapted to terrestrial life with new structures and reproductive strategies.

• Alternation of Generations: Diploid sporophyte (2n) produces haploid spores; haploid gametophyte (n) produces gametes.

• Adaptations: Apical meristems, waxy cuticle, lignified cell walls.

• Charophytes: Share traits with land plants.

• Derived Traits: Multicellular embryos, walled spores, gametangia, apical meristems.

• Mosses: Dominant gametophyte form.

• Ferns: Dominant sporophyte form; vascular tissues, flagellated sperm, heart-shaped gametophyte.

• Lycophytes: Microphylls (small leaves).

• Symbiosis: Fungi essential for plant colonization of land.

Seed Plants

• Sporophyte Dominance: Most visible form is diploid.

• Monocots vs. Eudicots: Monocots have one cotyledon; eudicots have two.

• Heterospory: Megaspores (female), microspores (male).

• Seeds and Pollen: Adaptations for terrestrial life; pollen allows fertilization without water.

• Gymnosperms: Naked seeds on cones; no fruits or flowers.

• Conifers: Cone-bearing, needlelike leaves.

• Cycads: Palm-like, large compound leaves.

• Ginkgophytes: Ginkgo biloba; pollution-resistant, male and female trees.

• Gnetophytes: Vessel elements similar to angiosperms.

• Angiosperms: Fruits, flowers, double fertilization.

• Flower Parts: Carpel (female: stigma, style, ovary, ovule), stamen (male: filament, anther).

• Life Cycle: Alternation of generations; double fertilization produces endosperm.

• Complete vs. Incomplete Flowers: Complete have both male and female parts; incomplete have only one.

Comparison Table: Monocots vs. Eudicots

Chapter 28: Vascular Plant Structure and Growth

Plant Organs

• Roots: Absorb water/minerals; types include prop, aerial, storage, pneumatophores, buttress roots.

• Stems: Nodes, internodes, axillary/apical buds; modified stems include rhizomes, bulbs, stolons, tubers.

• Leaves: Monocots (parallel veins), eudicots (branched veins); simple vs. compound; adaptations include storage, tendrils, reproductive leaves, spines.

Plant Tissues

• Dermal: Epidermis, cuticle, periderm.

• Vascular: Xylem (water transport), phloem (sugar transport); stele is the vascular cylinder.

• Ground: Pith (internal), cortex (external).

Differentiated Plant Cells

• Parenchyma: Flexible, primary cell walls; divide and differentiate.

• Collenchyma: Uneven cell wall thickness; alive at maturity.

• Sclerenchyma: Secondary walls with lignin; dead at maturity.

Xylem and Phloem

• Xylem: Water conduction; tracheids (long, thin), vessel elements (tubular); dead at maturity.

• Phloem: Sugar conduction; sieve tube elements (lack organelles), companion cells (support).

Growth and Meristems

• Determinate vs. Indeterminate Growth: Meristems allow continuous growth.

• Primary Growth: Apical meristems (root, shoot).

• Secondary Growth: Lateral meristems; cork cambium produces suberin-rich cork.

• Bark: All tissues outside vascular cambium.

• Apical Dominance: Apical meristem suppresses axillary bud growth.

Leaf Anatomy

• Spongy Mesophyll: Gas exchange.

• Palisade Mesophyll: Photosynthesis.

• Epidermis: Upper and lower layers.

Vascular Tissue Arrangement

• Leaves: Parallel veins (monocots), branched (eudicots).

• Stems: Scattered (monocots), rings (eudicots).

• Roots: Ring in monocots, central "X" in eudicots.

Phase Changes and Organ Identity Genes

• Phase Changes: Morphological transitions in shoot apical meristem activity.

• ABC Hypothesis: Model for flower organ identity.

Chapter 30: Angiosperm Reproduction

Alternation of Generations

• Sporophyte (2n): Produces spores.

• Gametophyte (n): Produces gametes.

• Mosses: Gametophyte dominant.

Flower Structure

• Complete Flowers: Both male and female organs.

• Incomplete Flowers: Only one type of sex organ.

• Whorls: Calyx (sepals), corolla (petals), androecium (stamens), gynoecium (carpels).

Double Fertilization and Endosperm

• Double Fertilization: One sperm fertilizes the egg; another fuses with two nuclei to form triploid endosperm.

• Endosperm: Triploid tissue; provides energy for embryo.

Pollination

• Agents: Wind, insects, water, birds, bats.

Seed Anatomy

• Hypocotyl: Below seed leaf (cotyledon).

• Epicotyl: Above cotyledon.

• Radicle: Embryonic root.

• Coleoptile: Protective sheath in grasses.

Seed Dormancy and Germination

• Vernalization: Cold exposure breaks dormancy.

• Scarification: Physical damage to seed coat (e.g., passage through animal gut).

• Germination: Triggered by water, warmth, longer days.

Fruit Structure and Types

• Exocarp: Outer layer.

• Mesocarp: Fleshy, edible part.

• Endocarp: Inner layer (e.g., almond).

• Types: Simple, aggregate, multiple, accessory fruits.

Seed and Fruit Dispersal

• Wind, animals, water.

Plant Propagation

• Cloning: Cuttings.

• Apomixis: Asexual seed development.

• Grafting: Scion (grafted part) onto stock (rooted plant); layering (root development from bent limb).

Breeding and Genetic Engineering

• Plant breeding and genetic engineering are used to improve crops and reduce world hunger.

Additional info: Academic context and explanations were expanded for clarity and completeness. Table entries and some details were inferred for completeness.