Cell Biology for the MCAT

Cell Structure

• Nucleus: Contains DNA, site of transcription
• Mitochondria: ATP via oxidative phosphorylation
• Rough ER: Ribosome-studded, protein synthesis
• Smooth ER: Lipid synthesis, detoxification
• Golgi: Modifies, sorts, packages proteins

Membrane Transport

• Passive: Diffusion, osmosis, facilitated — no energy, down gradient
• Active: Na⁺/K⁺ ATPase (3 Na⁺ out, 2 K⁺ in per ATP)
• Endocytosis: Phagocytosis, pinocytosis, receptor-mediated
• Exocytosis: Vesicle fusion with membrane

Cell Signaling

• GPCRs: G-protein coupled receptors → second messengers (cAMP, IP3, Ca²⁺)
• RTKs: Receptor tyrosine kinases — dimerize and autophosphorylate

Cell Cycle

G1 → S (DNA synthesis) → G2 → M (mitosis) Checkpoints at G1/S, G2/M, and metaphase