Chapter 3 Part 2: Cells: Eukaryotic Cell Structure

"Eu-" = true, "karyote" = nut ⇒ “true nucleus”
- Presence of a membrane-bound nucleus is the diagnostic trait.
- Rare exception: mature mammalian red blood cells (RBCs) lose their nuclei but are still part of a eukaryotic organism → biological “pass.”
Increased complexity relative to prokaryotes
- More internal membranes → more membrane-bound organelles.
- Compartmentalization: creation of specific micro-environments ("little pockets") that specialize in distinct tasks.
- Primary purpose of nucleus: protect DNA.
Cellular organization
- May be unicellular (e.g., many Protista; yeast in Kingdom Fungi) or multicellular (plants, animals, most fungi, etc.)
- Domain system:
- Domain Bacteria → prokaryotes
- Domain Archaea → prokaryotes
- Domain Eukarya → ALL eukaryotic organisms (no overlap, no middle ground).

Fungal and protistan cells resemble animal or plant archetypes, but lecture focuses on the two most familiar:
- Animal cells
- Plant cells

Nucleus (envelope, pores, nucleolus, chromatin)
Endoplasmic reticulum (ER)
- Rough ER (ribosomes attached)
- Smooth ER (no ribosomes)
Ribosomes (attached & free-floating)
Golgi apparatus / Golgi vesicles
Mitochondria (≈ size of bacteria)
Lysosomes (animal-specific)
Peroxisomes (mentioned but not detailed)
Vacuoles (small & variable in animals; single large “central vacuole” in plants)
Cytoplasm (cytosol + organelles)
Centrosome / Centrioles (animal-specific; division)
Cytoskeleton (microfilaments, intermediate filaments, microtubules)

Instructor’s humor: outline looks like a mouse being filleted (eye + limbs).
Mislabeling issue: many generic diagrams add a flagellum
- Reality: almost all animal cells lack flagella; sperm are the lone exception.
Recommended resources: downloadable Canvas diagram superior to textbook’s small image; ~3,000 alternatives online.

Cell wall (outside the plasma membrane)
Chloroplasts (photosynthesis)
Large central vacuole (water & solute storage, turgor pressure)
Otherwise shares most organelles with animal cells (nucleus, ER, Golgi, mitochondria, ribosomes, cytoskeleton, etc.)

Shared
- Nucleus
- Mitochondria
- Ribosomes (same type as prokaryotes; underscores universal necessity of protein synthesis)
- Endoplasmic reticulum (rough & smooth)
- Golgi apparatus
- Cytoskeleton
Animal-specific
- Lysosomes (digest old cellular parts, not lunch)
- Centrioles (within centrosome; spindle formation in mitosis/meiosis)
Plant-specific
- Cell wall (rigid support)
- Large central vacuole
- Chloroplasts (photosynthesis)
- Alternative mechanism for chromosome movement → no centrioles

Useful metric conversions
- $1\,\mu m = 10^{-6}\,\text{m}$
- $1\,nm = 10^{-9}\,\text{m}$
Macro- to micro-examples (selected from instructor’s chart)
- Ostrich egg → largest single cell known
- Chicken egg > Frog egg (≈10× human egg) > Human egg ≈ Pollen grain (pine pollen coats cars yellow)
- Typical plant/animal cell: $10\,\mu m\,–\,100\,\mu m$
- Red blood cell < typical animal cell (and, hilariously, diagram still showed a flagellum—ignore)
- Mitochondrion ≈ size of average bacterium (important evolutionary clue, to be discussed later)
- Viruses (smallpox, influenza, polio) ≈ $20\,–\,300\,nm$
- Proteins ≈ $10\,nm$ ; DNA double helix diameter ≈ $2\,nm$
- Water molecule ≈ $0.28\,nm$
Microscopy limits (visualized on chart)
- Light microscope: can resolve down to large viruses (~flu size)
- Electron microscope: proteins, lipids; still cannot resolve atoms
- X-ray crystallography & related: atomic-level detail

Terminology
- Cytosol = liquid component
- Organelles = membrane-bound or structural bodies suspended
- Cytoplasm = cytosol + organelles (everything internal to plasma membrane except the nucleus contents if one is distinguishing nucleoplasm)
Roles
- Site of numerous enzymatic reactions (metabolic pathways in “open solution”)
- Temporary storage: enzymes, nucleotides, ions, etc. (“push it off to the side” mentality)

Centrosome in non-dividing cell = pair of barrel-shaped centrioles at one location.
At onset of mitosis/meiosis
- Centrosome duplicates
- Centrioles migrate to opposite poles
- Microtubule-based spindle fibers assemble → attach to chromosomes → orchestrate segregation.
Plant cells: accomplish chromosome movement without centrioles; mechanism covered in later lectures.

Active recall: draw a blank cell on paper, label everything you can from memory, then cross-check against the official list/diagram.
Focus on "big picture" connections: which organelles share membranes, how size relates to function, etc.

Hummingbird outside during recording—biology humor on “audience diversity.”
Yeast as the beloved unicellular fungus (exception to general “fungi = multicellular” guideline).
Recurrent misuse of the term “flagellum” in stock animal-cell images; only sperm cells qualify in the animal kingdom.
Instructor’s childhood car (blue) turned yellow by pine pollen → real-world example of pollen grain size.

Importance of size scales in medical pathology (virus vs. bacterium diagnostics; microscopy choice).
Cell-type differences guide treatments: plant cell wall = target of antibiotics/antifungals; animal cell lysosomes = role in neurodegenerative disease research, etc.

Part 3 of lecture will continue organelle discussions (expect deeper dives into nucleus function, ER roles, Golgi trafficking, mitochondria/chloroplast endosymbiosis, etc.).