🧫 BIOL-7002 – Week 2: A Tour of the Cell Review

Microscopy Basics 🔬

• Magnification → makes objects look bigger.

• Resolution → clarity; the ability to distinguish 2 points as separate.

• Contrast → difference in light/dark to see details.
  Key idea: High magnification without resolution = blurry.
  Analogy: Zooming in on a low-quality pic doesn’t make it clearer.

Types of Microscopy

• Light microscopy (LM): Uses visible light, up to ~1000× magnification. Can see live cells.

• Electron microscopy (EM): Uses electrons, higher resolution.

  • SEM (scanning EM): 3D surface images.

  • TEM (transmission EM): Internal cell structures.
    Analogy: LM = Snapchat selfie cam, EM = professional DSLR camera.

Cell Fractionation (Centrifugation)

• Technique to break cells apart & separate organelles by size/density.

• Steps:

  • Homogenization → break cells.

  • Spin at different speeds (differential centrifugation).

  • Larger/heavier organelles pellet first, lighter ones later.

• Pellet = solid stuff at bottom (organelles).

• Supernatant = liquid above.
  Analogy: Like shaking trail mix and the big nuts fall to the bottom first.

Cell Size & Surface Area 📏

• Most cells: 1–100 μm.

• Surface area:volume ratio (S/V): Higher ratio = better exchange with environment.

• Small cells are more efficient for nutrient/waste exchange.
  Analogy: A skinny fry cooks faster than a baked potato because of surface area.

Prokaryotic vs Eukaryotic Cells

• Prokaryotes: No nucleus, DNA in nucleoid, smaller, simpler (ex: bacteria).

• Eukaryotes: DNA in nucleus, membrane-bound organelles, larger, more complex.

Plant vs Animal Cells 🌱🦊

• Plant cells: Cell wall, chloroplasts, central vacuole, plasmodesmata.

• Animal cells: Lysosomes, centrosomes, flagella (rare in plants).

Plasma Membrane

• Made of phospholipid bilayer + proteins + carbs.

• Hydrophilic heads face out; hydrophobic tails face in.
  Analogy: Like a water balloon with proteins floating inside the “skin.”

The Nucleus 🧬

• Surrounded by nuclear envelope (double membrane).

• Nuclear pores regulate entry/exit of molecules.

• Nuclear lamina: Protein network that maintains shape.

• Nucleolus: Makes ribosomal RNA (rRNA) + ribosome subunits

Ribosomes

• Free ribosomes: Float in cytosol → make proteins for use inside cell.

• Bound ribosomes: Attached to ER → make proteins for secretion/membranes.
  Analogy: Free = cooking for yourself; Bound = cooking for delivery.

Endoplasmic Reticulum (ER)

• Rough ER (RER): Ribosomes attached; makes proteins for secretion.

• Smooth ER (SER): No ribosomes; makes lipids, detox, stores Ca²⁺.

• Continuous with nuclear envelope.

Golgi Apparatus 📦

• Stack of flattened sacs (cisternae).

• Cis face: Receiving side.

• Trans face: Shipping side.

• Modifies, sorts, ships proteins/lipids.
  Analogy: Amazon warehouse — packages come in, get labeled, and sent out.

Lysosomes 🗑

• Membrane sacs with digestive enzymes.

• Functions:

  • Phagocytosis: Digest food.

  • Autophagy: Recycle damaged organelles.
    Analogy: Lysosome = recycling/trash center of the cell.

Vacuoles

• Central vacuole (plants): Stores water, ions, toxins, pigments. Maintains turgor pressure.

• Food vacuoles: Temporary storage for digestion.

Mitochondria 🔋

• Double membrane; inner folds = cristae (increase surface area).

• Matrix: contains enzymes, DNA, ribosomes.

• Site of cellular respiration (makes ATP).

• Evidence for endosymbiosis: has DNA + ribosomes.

Peroxisomes

• Single membrane.

• Break down fatty acids, detoxify harmful compounds.

• Produce hydrogen peroxide (H₂O₂), then break it into water.

Cytoskeleton 🕸

• Network of fibers for support, movement, organization.

• Microtubules (25 nm): Tubulin. Shape, cell division, motor protein “tracks” (kinesin/dynein).

• Microfilaments (7 nm): Actin. Muscle contraction, cell motility.

• Intermediate filaments (8–12 nm): Keratin. Anchor organelles, maintain shape.
  Analogy:

• Microtubules = highways.

• Microfilaments = zip lines.

• Intermediate filaments = scaffolding.

Cell Junctions

• Plasmodesmata (plants): Channels for cell-cell communication.

• Tight junctions (animals): Seal between cells.

• Desmosomes: Anchor cells together.

• Gap junctions: Communication channels between animal cells.