Eukaryotic Cells, Fungal Biology & Related Vocabulary

Evolutionary Timeline & Common Ancestry

• Earliest prokaryotic ("karyotic" in lecture) cells appeared ≈ (4\,\text{BYA}).

  • Separate lineages of \text{Archaea} and \text{Bacteria} already possessed independent circular DNA.

• First definite eukaryotic cells arise ≈ 2\text{ BYA} after prokaryotes (≈ 2\text{ BYA} overall age ≈ 4.3\text{ BYA} from today).

• Progression: single-celled → colonial aggregates → true multicellular organisms with tissues & organs.

  • Multicellularity enabled specialization (muscles, stomach, liver, kidneys, …)

Endosymbiotic Theory & Organelles

• Endosymbiosis = formerly independent cells joined "inside" one another → permanent, mutually beneficial partnership.

  • Explains why mitochondria & chloroplasts contain their own circular DNA and 70\,\text{S} ribosomes.

  • Mnemonic from lecture: “If Archaea and Bacteria had a baby → Eukarya.”

• Key organelles derived from this process:

  • Mitochondrion: ATP production via aerobic respiration.

  • Chloroplast (photosynthetic eukaryotes): light-driven ATP + organic carbon synthesis; releases O_2.

Structural Components of a General Eukaryotic Cell

• Membrane-bound nucleus (houses chromosomal DNA).
• Cytoplasmic (plasma) membrane.
• Mitochondria.
• Endoplasmic reticulum (rough & smooth).
• Golgi apparatus.
• Free & bound ribosomes.
• Cytoskeleton (actin filaments, microtubules).
• Glycocalyx (extracellular matrix).
Optional / organism-specific:
• Cell wall (fungi, algae).
• Locomotor appendages (flagella, cilia).
• Chloroplasts (photosynthetic lines).

Locomotor Appendages

• Flagella

  • Larger & more complex than bacterial flagella.

  • Consist of 9!+!2 microtubule arrangement; whip-like motion.

• Cilia

  • Shorter, numerous; locomotion or sweeping functions.

  • Found on certain protozoa (e.g.
    Giardia) & on human epithelial cells (e.g.
    respiratory tract).

Surface Structures: Glycocalyx & Cell Walls

• Glycocalyx (extracellular matrix)

  • Direct environmental contact; roles in adhesion, protection, inter-cell communication & spacing.

  • Network of polysaccharides; appears as capsules, slime layers, or fibrous matrices.

• Cell Walls (in fungi & algae)

  • Rigid support for harsh habitats (UV, salinity, desiccation).

  • Composition: chitin or cellulose.
    • Cellulose also found in plants; indigestible to humans.
    • Chitin forms insect exoskeletons & some candy coatings (fun anecdote from class).

Nuclear Organization & Chromosomes

• Nucleus = cellular “control center.”

• Nucleolus: site of ribosomal RNA (rRNA) synthesis.

• Chromatin vs Chromosomes

  • Chromatin = diffuse DNA-protein material; condenses into chromosomes during division.

• Human karyotype: 46 chromosomes = 23 pairs.

  • Trisomy examples:
    • \text{Trisomy 21} → Down syndrome.
    • \text{Trisomy 13} → Patau syndrome (rocker-bottom feet, severe developmental delay).

• Histones: DNA-wrapping proteins; translocations involving histones can trigger leukemias.

• Cell division

  • Mitosis: somatic cell duplication.

  • Meiosis: gamete (sperm/egg) formation.

Endomembrane System

• Rough ER (RER)

  • Studded with ribosomes → protein synthesis for secretion or membrane insertion.

• Smooth ER (SER)

  • Lipid synthesis & detoxification (briefly implied).

• Golgi Apparatus

  • Flattened cisternae; receives "transitional vesicles" from ER.

  • Modifies, sorts, packages proteins/lipids.

  • Products exit by:
    • Exocytosis (secretory vesicles).
    • Retention for intracellular use (lysosomes, enzymes, hormones).

• Lysosomes: acidic vesicles for digestion of toxins, microbes, cellular debris (“cleanup crew”).

• Vacuoles: storage of fluid or solids awaiting digestion, excretion, or reserve.

Protein Synthesis & Ribosomes

• Eukaryotic ribosome = 80\,\text{S} (60\,\text{S} + 40\,\text{S} subunits).

• Bacterial ribosome = 70\,\text{S} — critical drug-target difference.

• mRNA carries coding info; tRNA delivers amino acids; ribosome catalyzes peptide bond formation.

Cytoskeleton

• Network of actin filaments & microtubules.

  • Anchors organelles, guides vesicle traffic, confers flexibility / motility.

  • Enables cell shape changes & adaptation to environment.

Diversity of Eukaryotic Life-Forms

• Protozoa (unicellular parasites) — e.g.
Giardia.
• Helminths (multicellular parasites) — e.g.
tapeworms; termed “helminths” when multicellular.
• Fungi & Algae — may be uni- or multicellular depending on species & strain.

Fungal Biology

Macroscopic vs Microscopic

• Macroscopic: mushrooms, puffballs, bracket fungi.

• Microscopic: molds & yeasts.

Yeast Characteristics

• Unicellular; reproduce asexually by budding → "mini-me" daughter cell.

• Produce pseudohyphae when buds remain attached.

Mold Morphology

• Hypha (pl. hyphae): long thread-like filament; fungal analogue of "branch."

• Mycelium: intertwined mass of hyphae forming body/colony.

• Septa: cross-walls dividing hyphae into segments.

• Dimorphic fungi: switch between yeast-like & mold-like forms depending on environment (temp, nutrients).

Nutrition Modes

• Heterotrophic: broad substrate utilization.

• Saprobe (saprotroph): consumes dead organic matter (plant/animal) — vital decomposers; “don’t panic, it’s organic.”

• Parasite: lives on/in living host; derives nutrients without benefit to host.

Reproduction & Spores

• Simple outward hyphal growth.

• Fragmentation: hypha breaks into pieces → new colonies.

• Sporangiospore production (sporangium atop sporangiophore) — e.g.
  bread mold.

• Spores = reproductive units for dispersal & germination.

Medical & Environmental Relevance

• Example infections:

  • Tinea pedis (athlete’s foot) \Rightarrow hyphal invasion of skin.

  • Bread mold spores: ingestion typically harmless; inhalation may cause respiratory disease, esp. in allergies or immunodeficiency.

• Routes of infection

  1. Community-acquired (soil, water, dust storms).

  2. Nosocomial (hospital-acquired).

  3. Opportunistic in immunocompromised (transplants, cancer therapies).

• Clinical consequences: allergies, mycotoxicosis (neurological effects), systemic mycoses.

Beneficial Applications

• Decomposition & nutrient cycling.

• Antibiotics (e.g.
  penicillin).

• Fermentation: alcohol, bread leavening.

• Food flavoring, vitamin production.

Ethical / Practical Implications

• Understanding endosymbiosis clarifies evolutionary relatedness & guides drug targeting (e.g.
  mitochondrial toxicity, ribosome differences).

• Immunosuppressive therapies demand fungal surveillance.

• Industrial use of fungi raises GMO & allergen-exposure considerations.

Quick Reference Equations & Numbers

• Appearance of prokaryotes: \approx4\,\text{BYA}.
• Emergence of eukaryotes: \approx2\,\text{BYA} after prokaryotes → \approx2\,\text{BYA} present.
• Human chromosomes: 46 = 23 \times 2.
• Ribosomal sizes: 80\,\text{S} = 60\,\text{S}+40\,\text{S} (eukaryote), 70\,\text{S} (bacterium, mitochondrion, chloroplast).