Eukaryotes, Fungi, and Algae Lecture Notes

Eukaryotic Cells and Fungi

Key Terms in Eukaryotic Cells

  • Nucleolus: A dense region within the nucleus where ribosomal RNA is synthesized.

  • Nucleus: The membrane-bound organelle that contains genetic material.

  • Plasma Membrane: The lipid bilayer that surrounds the cell, controlling the movement of substances in and out.

  • Cytoplasm: The gel-like substance within the cell membrane, excluding the nucleus, that contains organelles.

  • Nuclear Envelope: The double membrane structure that encloses the nucleus.

  • Nuclear Pore: Openings in the nuclear envelope that allow transport between the nucleus and cytoplasm.

  • Flagellum: A long, whiplike structure that aids in cell movement.

  • Centrosome: An organelle that serves as the main microtubule organizing center.

  • Microfilament: A component of the cytoskeleton, providing structural support to cells.

  • Ribosome: A cellular structure responsible for protein synthesis.

  • Mitochondrion: The powerhouse of the cell, generating ATP through cellular respiration.

  • Microtubule: A component of the cytoskeleton involved in various cellular functions, including shape and transport.

  • Rough Endoplasmic Reticulum (RER): An organelle involved in protein synthesis and processing, studded with ribosomes.

  • Smooth Endoplasmic Reticulum (SER): An organelle involved in lipid synthesis and detoxification processes.

  • Golgi Apparatus: An organelle that modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.

  • Peroxisome: An organelle that contains enzymes for detoxifying harmful substances.

  • Cilia: Short hair-like structures that help in cell movement and the movement of materials across the cell surface.

  • Lysosome: An organelle that contains enzymes for digestion of cellular waste.

Overview of Fungi

  • Mycology: The study of fungi.

  • Fungi Characteristics:

    • Chemoheterotrophs: They decompose organic matter to obtain nutrients.

    • Can be aerobic (requiring oxygen) or facultatively anaerobic (can survive with or without oxygen).

Comparison of Fungi and Bacteria (Table 12.1)

  • Cell Type:

    • Fungi: Eukaryotic

    • Bacteria: Prokaryotic

  • Cell Membrane:

    • Fungi: Sterols present

    • Bacteria: Sterols absent, except in Mycoplasma

  • Cell Wall:

    • Fungi: Composed of glucans, mannans, and chitin (without peptidoglycan)

    • Bacteria: Composed of peptidoglycan

  • Spores:

    • Fungi: Both sexual and asexual reproductive spores

    • Bacteria: Endospores (not for reproduction); some asexual reproductive spores

  • Metabolism:

    • Fungi: Limited to heterotrophic; aerobic, facultatively anaerobic

    • Bacteria: Heterotrophic, autotrophic; aerobic, facultatively anaerobic, anaerobic.

Vegetative Structures of Fungi

Molds and Fleshy Fungi

  • Fungal Thallus: The body of fungi, composed of hyphae.

    • Hyphae: Filamentous structures.

    • Mycelium: A mass of hyphae.

    • Septate Hyphae: Contains cross-walls (septa).

    • Coenocytic Hyphae: Lacks septa, forming a continuous structure.

Yeasts

  • Non-filamentous and Unicellular.

    • Budding Yeasts: Divide unevenly.

    • Fission Yeasts: Divide evenly.

  • Dimorphic Fungi: Exhibit both yeast-like growth at 37°C and mold-like growth at 25°C.

Fungal Life Cycle

Asexual Spores

  • Produced via mitosis and cell division from hyphae of one organism:

    • Conidiospore: Not enclosed in a sac.

    • Arthroconidia: Fragmentation of septate hyphae.

    • Blastoconidia: Buds of the parent cell.

    • Chlamydoconidium: Spore within a hyphal segment.

    • Sporangiospore: Enclosed in a sac.

Sexual Spores

  • Result from the fusion of nuclei from two opposite mating strains:

    1. Plasmogamy: The haploid donor cell nucleus penetrates the cytoplasm of the recipient cell.

    2. Karyogamy: The (+) and (−) nuclei fuse to form a diploid zygote.

    3. Meiosis: The diploid nucleus produces haploid nuclei (sexual spores).

Nutritional Adaptations of Fungi

  • Fungi thrive at a pH of 5.

  • Adapted to high sugar and salt concentrations; resistant to osmotic pressure.

  • Capable of growth in low moisture content.

  • Can metabolize complex carbohydrates.

Medically Important Fungi

  • Zygomycota: Conjugation fungi with coenocytic hyphae and asexual reproduction via sporangiospore; sexual reproduction via zygospore.

  • Microsporidia: Obligate intracellular parasites; no observed sexual reproduction.

  • Ascomycota: Sac fungi with septate hyphae; produces conidiospore asexually and ascospores sexually.

  • Basidiomycota: Club fungi with septate hyphae; produces basidiospores sexually.

Fungal Diseases

  • Mycosis: A fungal infection affecting various body systems:

    • Systemic Mycoses: Deep within the body.

    • Subcutaneous Mycoses: Beneath the skin.

    • Cutaneous Mycoses: Affecting hair, skin, and nails.

    • Superficial Mycoses: Localized infections.

    • Opportunistic Mycoses: Generally harmless but pathogenic in immunocompromised hosts.

Economic Importance of Fungi

  • Utilization of Saccharomyces cerevisiae in bread making, winemaking, and vaccine development.

  • Production of Trichoderma cellulase for the degradation of cellulose.

  • Source of Taxomyces, which produces taxol, a chemotherapy drug.

  • Use of Entomophaga and Coniothyrium minitans in pest control.

Lichens

  • Mutualistic relationship between a green alga (or cyanobacterium) and sac fungi.

    • Thallus Components:

    • Medulla: Hyphae grown around algal cells.

    • Rhizines (holdfasts): Hyphae projections below the body.

    • Cortex: A protective coating over the algal layer.

    • Types of lichens:

    • Crustose: Encrusted.

    • Foliose: Leaf-like.

    • Fruticose: Finger-like structures.

    • Economic Importance: Dyes, antimicrobial properties (Usnea), litmus, and food for herbivores.

Algae

  • Unicellular or filamentous photoautotrophs lacking true roots, stems, or leaves. Aquatic organisms, requiring water for growth and reproduction.

  • Characteristics of Selected Algae (Table 12.3):

    • Brown Algae (Phaeophyta): Cell walls composed of cellulose and alginic acid; multicellular, producing algin used as a food thickener.

    • Red Algae (Rhodophyta): Multicellular with branched thalli; harvested for agar and carrageenan.

    • Green Algae (Chlorophyta): Gave rise to terrestrial plants.

    • Diatoms: Silica cell walls that store oil and produce neurotoxin domoic acid, leading to neurological diseases.

    • Dinoflagellates: Produce toxins leading to paralytic shellfish poisoning.

    • Oomycota (Water molds): Chemoheterotrophic decomposers associated with various plant diseases.

Protozoa

  • Unicellular eukaryotes inhabiting water and soil with complex life cycles.

  • Trophozoite: Feeding and growing stage.

  • Asexual reproduction by fission, budding, or schizogony; sexual reproduction via conjugation.

  • Cysts: Protective structures enabling survival during adverse conditions.

Medically Important Protozoa

  • Classifications include Excavata (Diplomonads, Parabasalids, Euglenozoa), Amebae, Apicomplexa, and Ciliates, each with specific characteristics and diseases.

Helminths (Parasitic Worms)

  • Two phyla: Platyhelminthes (flatworms) and Nematoda (roundworms).

  • Helminths often have specialized adaptations for living in hosts, including reduced digestive systems, complex reproductive systems, and various life cycles involving intermediate and definitive hosts.

Vectors and Disease Transmission

  • Arthropods: Segmented animals with hard exoskeletons acting as vectors for microorganisms.

  • Transmission Mechanisms:

    • Mechanical Transmission: Direct transfer without multiplication.

    • Biological Transmission: Pathogen multiplies within the vector.

Conclusion

  • Understanding the structure and function of eukaryotic cells, fungi, algae, protozoa, and helminths is crucial in microbiology, especially in medical and environmental contexts.