Cell Biology

🏥 Cell Biology

Part 1 of 7 — Cell Structure & Organelles

Eukaryotic cells have membrane-bound organelles; prokaryotic cells do not.

Nucleus: contains DNA; Mitochondria: ATP via oxidative phosphorylation; ER: protein/lipid synthesis.

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Key Insight: Rough ER: ribosome-studded, protein synthesis; Smooth ER: lipid synthesis, detoxification.

MCAT Tip: Golgi apparatus: modifies, sorts, and packages proteins for secretion or intracellular use.

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Membrane Transport

Part 2 of 7 — Membrane Transport

Passive transport: diffusion, osmosis, facilitated diffusion — no energy required, down concentration gradient.

Active transport: Na+/K+ ATPase (3 Na+ out, 2 K+ in per ATP), against gradient.

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Key Insight: Endocytosis: phagocytosis (solids), pinocytosis (fluids), receptor-mediated (specific molecules).

MCAT Tip: Exocytosis: vesicles fuse with membrane to release contents (neurotransmitters, hormones).

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Cell Signaling

Part 3 of 7 — Cell Signaling

Signal transduction: ligand binds receptor, activates intracellular cascade, produces cellular response.

G-protein coupled receptors (GPCRs): activate G proteins which activate effector enzymes.

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Key Insight: Receptor tyrosine kinases (RTKs): dimerize and autophosphorylate upon ligand binding.

MCAT Tip: Second messengers: cAMP, IP3, DAG, Ca2+ — amplify the signal inside the cell.

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Cell Cycle & Division

Part 4 of 7 — Cell Cycle & Division

Cell cycle: G1 (growth), S (DNA synthesis), G2 (prep for division), M (mitosis).

Mitosis: prophase, metaphase, anaphase, telophase — produces 2 identical diploid cells.

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Key Insight: Meiosis: two divisions producing 4 haploid gametes; crossing over creates genetic diversity.

MCAT Tip: Checkpoints: G1/S (DNA damage?), G2/M (replication complete?), metaphase (all chromosomes attached?).

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Apoptosis & Regulation

Part 5 of 7 — Apoptosis & Regulation

Apoptosis: programmed cell death — caspase cascade leads to orderly cell dismantling.

Intrinsic pathway: mitochondrial stress releases cytochrome c, activating caspase-9.

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Key Insight: Extrinsic pathway: death ligands (FasL, TNF) bind death receptors, activating caspase-8.

MCAT Tip: Cancer: loss of apoptosis regulation + gain of proliferation signals = uncontrolled growth.

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Stem Cells & Differentiation

Part 6 of 7 — Stem Cells & Differentiation

Stem cells: self-renewing, can differentiate into specialized cell types.

Totipotent: can become any cell (zygote); Pluripotent: any cell except placenta (embryonic stem cells).

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Key Insight: Multipotent: limited range (hematopoietic stem cells make blood cells).

MCAT Tip: Differentiation is controlled by gene expression — same DNA, different genes active.

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Review & MCAT Practice

Part 7 of 7 — Review & MCAT Practice

Stem cells: self-renewing, can differentiate into specialized cell types.

Totipotent: can become any cell (zygote); Pluripotent: any cell except placenta (embryonic stem cells).

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Key Insight: Multipotent: limited range (hematopoietic stem cells make blood cells).

MCAT Tip: Differentiation is controlled by gene expression — same DNA, different genes active.

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