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Chapter 5 Notes: Eukaryotic Cells and Related Organisms

Endosymbiotic Theory

  • Explains how organelles evolved; organelles like mitochondria and chloroplasts were once independent prokaryotes.
  • Chloroplasts originated from photosynthetic bacteria; mitochondria from heterotrophic bacteria.
  • Evidence for endosymbiosis includes:
    • Organelles have their own DNA and hence unique proteins, separate from the nuclear genome.
    • Size and structure of mitochondria and chloroplasts resemble bacteria.
    • Symbiotic organisms exist today, supporting the plausibility of endosymbiotic relationships in the past.
  • Figure reference: Fig. 10.2 (illustrative support).

The Eukaryotic Cell: Overview and Key Components

  • The eukaryotic cell combines features of plants and animals in a single framework; organelles are compartmentalized for specialization.
  • Plant cell vs. animal cell (highly schematic composite):
    • Plant cell components:
    • Cell wall, central vacuole, plastids (chloroplasts) for photosynthesis and storage, peroxisomes, mitochondrion, Golgi, ER (RER and SER), cytoplasm, ribosomes, plasma membrane, microfilaments, microtubules.
    • Nucleolus and nucleus present.
    • Animal cell components:
    • Flagellum (in some cells), nucleus with nucleolus, Golgi, cytoplasm, basal body, microfilaments, lysosome, centrosome with centriole and pericentriolar material, ribosomes, microtubules, peroxisome, rough and smooth ER, mitochondrion, plasma membrane.
  • Shared organelles and roles:
    • Nucleus with nucleolus (ribosome assembly) and chromatin (DNA + protein).
    • Nuclear envelope (double membrane) with pores for molecular traffic.
    • Endoplasmic reticulum (ER) with cisterns: rough ER studded with ribosomes for protein synthesis; smooth ER for lipid and carbohydrate metabolism; vesicles bud off to Golgi.
    • Golgi complex functions: docks, sorts, tags, and packages proteins and lipids; secretory vesicles and vesicles from rough ER transit through Golgi.
    • Lysosomes (digestive system): hydrolytic enzymes at low pH; Tay-Sachs disease arises from missing enzyme.
    • Vacuoles: storage of water, food, salts, pigments, and wastes; central vacuole particularly large in plants.
    • Peroxisomes: detox centers breaking down harmful small organic molecules (e.g., ethanol, hydrogen peroxide); contain crystalline cores (e.g., urate oxidase).
    • Mitochondria: powerhouse producing ATP; double membrane with cristae, matrix, and intermembrane space.
    • Chloroplasts (plants only): plastids for photosynthesis; pigments to make glucose; triple membrane arrangement with grana (thylakoid stacks), stroma, and thylakoid lumen.
    • Cytoskeleton: microfilaments and microtubules providing structure and transport.

Flagella and Cilia

  • Structure: Flagellum and cilia are composed of microtubules arranged in a 9+2 pattern.
  • Mechanism: Dynein motor proteins use ATP to slide microtubules against each other; sliding is converted into the bending motion that produces whip-like movement of the cell.
  • Key point: This 9+2 arrangement enables coordinated motility in many eukaryotic cells.

Nucleus and Nuclear Organization

  • Nucleus acts as the control center; houses genetic material organized as chromatin.
  • Nucleolus: ribosome assembly site.
  • Nuclear envelope: a double membrane with nuclear pores that regulate traffic of molecules between nucleus and cytoplasm.

Endoplasmic Reticulum (ER)

  • ER as manufacturing center; consists of cisterns (flattened tubes).
  • Rough ER: ribosome-studded; synthesizes proteins destined for secretion or membranes.
  • Smooth ER: lacks ribosomes; involved in lipid and carbohydrate metabolism; detoxification processes.
  • Vesicles bud from ER and traffic to the Golgi.

Golgi Complex

  • “Post Office” of the cell: docks, sorts, tags, and packages proteins and lipids for delivery.
  • Involves secretory vesicles and transfer vesicles from the rough ER.

Vacuoles

  • Storage and recycling center for water, food, salts, pigments, and wastes.
  • Very large in plant cells (central vacuole).

Lysosomes

  • Contain hydrolytic enzymes optimized for low pH; digest macromolecules.
  • Tay-Sachs disease example: missing enzyme leads to accumulation of undigested substrates.

Mitochondrion: Powerhouse

  • ATP production site.
  • Structure: double membrane forming cristae; matrix; inner membrane space; intermembrane space.
  • Diagram features: matrix; cristae; inner vs outer membranes.

Chloroplast: Solar Power Plant

  • Found in plants; plastid; conducts photosynthesis to produce glucose.
  • Structure: triple membrane arrangement yields grana (thylakoid stacks) and stroma; thylakoid lumen.
  • Pigments drive light capture for carbohydrate synthesis.

Peroxisome: Detox Center

  • Breaks down harmful small organic molecules (e.g., ethanol, hydrogen peroxide).
  • Anatomy: lipid bilayer; urate oxidase; crystalline core.

Fungi: Basic Biology and Classification

  • Nutrition: aerobic chemoheterotrophs that absorb nutrients from the environment.
  • Pathogenic potential: many cause opportunistic infections.
  • Life forms: yeasts are unicellular; molds are multicellular.
  • Reproduction: both asexual and sexual modes exist.

Fungal Cell and Mycelial Organization

  • Body plan: body is a mycelium composed of tubular filaments called hyphae.
  • Hyphae cell walls contain chitin.
  • Septate vs. coenocytic hyphae:
    • Septate: incomplete cross walls.
    • Coenocytic: hyphae without septa.

Mold Anatomy and Reproduction

  • Reproductive body of molds: fruiting body.
  • Spores produced for dissemination.
  • Spores can be dispersed long distances; puffballs disperse trillions of spores in bursts.
  • Spore travel distance example: some 99% of spores fall within 100 meters (approx. 328 feet) of the parent puffball.

Fungal Reproduction Types

  • Asexual reproduction: haploid spores produced in sporangia or at hyphae tips (conidia); fission or budding by unicellular fungi; breakage of mycelium.
  • Sexual reproduction: many mating types; cytoplasmic and nuclear fusion (plasmogamy and karyogamy); diploid stages arise; spores produced after meiosis.

Zygomycetes (Bread Molds): Rhizopus

  • Reproduction:
    • Asexual: haploid hyphae produce sporangia that release haploid spores.
    • Sexual: haploids of opposite mating types fuse to form a zygospore (diploid); zygospore undergoes meiosis to produce sexual spores.
  • Life cycle illustration includes stages: aerial hypha, sporangium, sporangiospores, plasmogamy, zygospore, karyogamy, meiosis, spore release, germination.
  • Key terms: sporangium, sporangiophore, sporangiospores, zygospore, zygosporangium.
  • Scale example in figure: sporagiophore/sporangium size around 25 μm (Rhizopus stolonifer).

Ascomycetes (Sac Fungi)

  • Example: Candida (causes yeast infections).
  • Reproduction:
    • Asexual: haploid hyphae produce conidia that release haploid spores.
    • Sexual: mating produces an ascus that releases sexual ascospores.
  • Structures: conidiophore, conidia; ascus and ascospores.

Basidiomycetes (Club Fungi)

  • Example: Agaricus (button mushroom).
  • Reproduction:
    • Asexual: generally no spores produced; mainly vegetative growth.
    • Sexual: mating produces a fruiting body (mushroom) containing basidiospores.
  • Structures: basidium, basidiospores; fruiting body (mushroom).

Life Cycles in Fungi: Summary of Sexual vs Asexual Cycles

  • Asexual reproduction: mycelium generates spores by mitosis; spores disperse and germinate into new hyphae.
  • Sexual reproduction: two haploid hyphae fuse cytoplasm (plasmogamy) forming a dikaryotic mycelium; later karyogamy occurs to form a diploid nucleus; meiosis yields haploid spores.

Parasites and Eukaryotic Parasitology

  • Types of hosts:
    • Intermediate host: harbors the asexual (juvenile) stage.
    • Definitive host: harbors the sexual (adult) stage.
  • Immune evasion strategies used by parasites:
    • Encystment: formation of a resistant outer shell to survive harsh environments.
    • High mutation rate of surface antigens to escape immune detection.
    • Antigen decoys: molecules released to elicit inappropriate immune responses.
    • Hiding inside host cells to avoid immune surveillance.
  • Context: Eukaryotic parasitology involves studying such host–parasite interactions and strategies.

Protists: A Broad Overview

  • Protists are a diverse collection of mostly unicellular organisms that can live in colonies.
  • Subgroups:
    • Algae: plant-like, photosynthetic; pigments determine types (red, brown, green).
    • Protozoans: animal-like, chemoheterotrophs; some are free-living.
    • Slime molds: fungal-like in lifestyle.
  • Key points: protists can reproduce sexually or asexually; many require aquatic environments.

Algae: Photosynthetic Protists

  • Characteristics:
    • Photosynthetic; pigment-based classification (e.g., red, brown, green algae).
    • Reproduce both sexually and asexually.
    • Require water for growth and dispersal.
  • Ecological role: primary producers in many ecosystems.

Dinoflagellates: Red Tide and Toxins

  • Flagellated protists with very tough cell walls; produce potent toxins that can accumulate in fish and shellfish.
  • Red tide: seasonal algal blooms caused by some dinoflagellates.
  • Alexandrium as a notable genus responsible for red tides.
  • Global concerns: red tides have been increasing due to global warming and over-fertilization.

Protozoa: Free-Living Chemoheterotrophs

  • Notable examples (likely from visual references): Paramecium, Euglena, Amoeba, Giardia, Trypanosoma, Plasmodium, Stentor, Toxoplasma.
  • General traits: chemoheterotrophs; reproduce asexually, some sexually; many are free-living.

Trypanosomes and Giardia

  • Trypanosomes: flagellated protozoa; many lack mitochondria in some life stages; often symbionts in digestive tracts of animals.
  • Giardia: a protozoan parasite causing traveler's diarrhea (often cited as an example of human disease from protists).

Amoebas

  • Morphology: amorphic, irregular shapes; move by pseudopods.
  • Example: Entamoeba, which can cause amoebic dysentery.

Animals: Worms and Arthropods

  • Major groups discussed:
    • Worms: flatworms (Platyhelminthes) including flukes (trematodes) and tapeworms (cestodes); roundworms (nematodes).
    • Arthropods: includes insects, arachnids, crustaceans.

Ascaris: Large Intestinal Roundworm

  • Habitat and transmission: Infects humans via ingestion of eggs from soil or contaminated food.
  • Notable facts: adult worms reside in the small intestine; female worms can produce up to 2\times 10^5 eggs per day.

Flukes (Trematodes) and Clonorchis sinensis

  • Anatomy: oral sucker is used for attachment.
  • Common genera: Clonorchis sinensis (asian liver fluke) as a representative.
  • Life stages: intestine, metacercaria (encysted form) in intermediate hosts.

Metacercaria and Lung Fluke Life Cycle

  • Lung fluke life cycle overview:
    • Cercariae leave snail and encyst as metacercaria in crayfish (intermediate host).
    • Infected crayfish are eaten by humans; metacercaria develop into adult flukes in the lungs.
    • Hermaphroditic adult fluke releases eggs into human lung.
  • Key steps and sizes:
    • Cercaria stage size around 0.5 mm.
    • Metacercaria forms in crayfish; human infection occurs through ingestion.
  • Lifecycle progression (condensed): snail (intermediate host) → cercaria → metacercaria in crayfish → human ingestion → adult fluke in lung → eggs excreted.

Tapeworms (Cestodes): Scolex and Proglottids

  • Anatomy: Scolex (head) for attachment; proglottids are the rest of the segments containing eggs.
  • Size example: scolex length around 1 mm; juvenile/hydatid cyst stages can occur in intermediate hosts.
  • Life cycle flow: adult tapeworm releases eggs into host; eggs ingested by intermediate host; larvae form cysts; definitive host ingests intermediate host and acquires adult tapeworm.
  • Notable mechanism: hydatid cysts as a hydatid cyst (brood capsule) in intermediate hosts; scolex can detach and form new tapeworms in the definitive host.
  • Visual cues from figures include hydatid cysts and scolex attachment.

Tapeworm Life Cycle ( summarized )

  • Stepwise flow (typical depiction):
    • 1 Adult tapeworm in definitive host releases eggs.
    • 2 Eggs excreted and ingested by intermediate host.
    • 3 Eggs hatch and larvae migrate to liver/lungs or other tissues.
    • 4 Larvae form hydatid cysts in intermediate host tissues.
    • 5 Definitive host ingests intermediate host containing cysts.
    • 6 Scolex attaches to intestinal wall of definitive host.
    • 7 Eggs/segments are released, starting cycle anew.
  • Typical sizes from figures: hydatid cysts and scolex structures are shown with scale indicators (e.g., around 1 cm scale; scolex near 1 mm in some images).

Arthropods as Vectors

  • Arthropod body plans:
    • Insects: three body regions (head, thorax, abdomen) and six legs.
    • Arachnids: two body regions (cephalothorax and abdomen) and eight legs.
    • Crustaceans: mainly aquatic with protective shells.
  • Role as disease vectors:
    • Vectors transmit parasites by transmitting eggs, larvae, or pathogens during blood meals or contact.
  • Example vectors pictured: Tick (arthropod with exoskeleton), Mosquito (insect), Lobster (crustacean) shown as part of vector imagery.
  • Exoskeleton is a defining feature enabling protection and motility in arthropods.

Health, Ecology, and Practical Relevance

  • Endosymbiosis provides a unifying framework for understanding organelle origin and the evolution of complex cells.
  • Fungal biology underpins both ecological roles (decomposers) and human health (pathogens, opportunistic infections).
  • Protists include major pathogens (e.g., Giardia, Plasmodium) and key ecological players (photosynthetic algae).
  • Parasitology highlights complex host–parasite interactions, life cycles with intermediate and definitive hosts, and immune evasion strategies.
  • Understanding life cycles (e.g., Ascaris, flukes, cestodes) informs public health strategies for prevention, diagnosis, and treatment.

Connections to Foundational Principles

  • Cell theory: eukaryotic cells are organized with membrane-bound organelles performing specialized functions.
  • Evolutionary biology: endosymbiotic theory explains the origin of mitochondria and chloroplasts.
  • Genetics and heredity: organelle DNA supports the concept of separate genetic systems within cells.
  • Ecology and disease: protists and helminths link cellular biology to ecosystem dynamics and human health.

Key Terms and Concepts to Remember

  • Endosymbiosis, mitochondrion, chloroplast, plastid, cristae, stroma, grana, thylakoid, central vacuole, cell wall, chitin, septate, coenocytic, mycelium, hyphae, sporangium, sporangiospores, conidia, plasmogamy, karyogamy, dikaryotic, zygospore, ascus, ascospores, conidiophore, basidiospores, basidium, sporangiophore, sporangiophore, hydatid cyst, scolex, proglottids, metacercaria, cercaria, miracidium, dauers, vectors, encystment, antigenic variation, antigen decoys.

Numerical and Size References (LaTeX)

  • Puffball spore dispersal range: ext{distance} o 2 ext{ meters}.
  • Spore dispersal statistic: 99 ext{\%} ext{ fall within } 100 ext{ meters} ext{ (or } 328 ext{ ft)}.
  • Ascaris fecundity: up to 2\times 10^5 \text{eggs per day}.
  • Sporangium size (Rhizopus stolonifer): 25\ \,\mu\text{m}.
  • Asexual/survival measurements: occasionally indicated scales around 0.8\text{ mm} for miracidium; 0.25\text{--}0.5\text{ mm} for metacercaria.
  • Ascus size (Ascomycetes): 40\ \mu\text{m}.
  • Basidium/basidiospores size in Basidiomycetes: 50\ \mu\text{m} (example measurement from figures).
  • Tapeworm length examples: 7.5\text{--}12\ \text{mm} for some adult segments.
  • Clonorchis and other fluke stages: cercaria size around 0.5\ \text{mm}; metacercaria size varies around similar scales.

Note for Study and Exam Prep

  • Focus on the hierarchical organization: organelles within eukaryotic cells, their specific roles, and how they integrate to support cellular function.
  • Understand the life cycles of major fungi groups and parasitic Helminths (Ascomycetes, Basidiomycetes, Zygomycetes) including the key structures involved in each cycle.
  • Be able to explain endosymbiotic theory and cite evidence (DNA, size/structure, existence of modern symbionts).
  • Recognize the ecological and medical relevance of protists and helminths, including transmission routes and host requirements.
  • Memorize organism examples and their key features (Candida, Rhizopus, Rhizopus zygospore cycle, Giardia, Trypanosoma, Plasmodium, Ascaris, Clonorchis, Diphyllobothrium if mentioned, Arthropod vectors).