Eukaryotic Cells
High-Yield Summary
- Eukaryotic cells have a membrane-bound nucleus and membrane-bound organelles; prokaryotes have neither.
- Mitochondria produce ATP, carry their own circular DNA/ribosomes, and are semi-autonomous — key evidence for the endosymbiotic theory.
- Rough ER makes/folds proteins for secretion or membranes; smooth ER makes lipids, detoxifies, and stores Ca²⁺.
- Golgi apparatus modifies (glycosylation, phosphorylation, sulfation) and ships proteins/lipids: enters at the cis face, exits at the trans face.
- Lysosomes digest waste with hydrolytic enzymes; peroxisomes break down fatty acids and use catalase to neutralize H₂O₂.
- Cytoskeleton: microfilaments (actin, cytokinesis), microtubules (tubulin, spindle/cilia/flagella), intermediate filaments (mechanical strength).
- Cells organize into tissue: epithelial covers/lines; connective supports and structures.
Key Terms
- Nuclear envelope
- Double membrane around the nucleus; nuclear pores regulate two-way traffic.
- Chromatin
- DNA + histones; euchromatin (loose, active) vs. heterochromatin (dense, inactive).
- Nucleolus
- Assembles ribosome subunits from rRNA; does not store DNA.
- Cristae
- Inner mitochondrial membrane folds that increase surface area for the electron transport chain.
- Endosymbiotic theory
- Mitochondria descended from an engulfed aerobic prokaryote.
- Cisternae
- The stacked membrane sacs making up the Golgi apparatus.
- 9+2 arrangement
- Microtubule pattern in cilia/flagella (9 pairs surrounding 2 central).
Rough ER vs. Smooth ER
| Rough ER | Smooth ER |
|---|---|
| Ribosome-studded | No ribosomes |
| Protein synthesis/folding for secretion, membranes, organelles | Lipid synthesis, detoxification, Ca²⁺ storage |
Lysosomes vs. Peroxisomes
| Lysosomes | Peroxisomes |
|---|---|
| Hydrolytic enzymes | Oxidative enzymes |
| Digest waste, damaged organelles, macromolecules; autolysis in programmed cell death | Break down fatty acids; catalase neutralizes H₂O₂ byproduct |
Golgi Protein Trafficking
- 1Vesicles from the smooth ER fuse at the cis face.
- 2Proteins/lipids are modified (glycosylation, phosphorylation, sulfation).
- 3Modified products are repackaged into vesicles budding from the trans face.
- 4Vesicles travel to the lysosome, the plasma membrane, or are released via exocytosis.
Common MCAT Trap
- Mitochondrial apoptosis (cytochrome c release → caspase cascade) is a distinct pathway from lysosomal autolysis — don't conflate the two.
- Rough ER vs. smooth ER, and lysosomes vs. peroxisomes, are classic "sounds similar, tested differently" pairs.
Quick Recall
What structurally distinguishes eukaryotic from prokaryotic cells?
Why are mitochondria called "semi-autonomous"?
Which organelle uses catalase to neutralize H₂O₂?