MDCAT Cell Structure & Function 2026 — Organelles, Membrane, & Cell Cycle

Organelles Quick Reference

• Nucleus — DNA storage, transcription. Has double membrane (nuclear envelope) with pores.
• Mitochondria — ATP via Krebs + ETC. Double membrane, inner highly folded (cristae). Has own DNA.
• Chloroplast — Photosynthesis (in plants). Double membrane + thylakoids inside.
• Rough ER — protein synthesis (ribosomes attached).
• Smooth ER — lipid synthesis, detoxification, Ca²⁺ storage. NO ribosomes.
• Golgi apparatus — modifies, packages, ships proteins from ER. Cis face receives, trans face dispatches.
• Ribosome — protein synthesis. 80S in eukaryotes (60S + 40S); 70S in prokaryotes.
• Lysosome — hydrolytic enzymes for intracellular digestion. Acidic interior (pH ~5).
• Peroxisome — oxidation reactions; breaks down fatty acids, H₂O₂.
• Cytoskeleton — microtubules + intermediate filaments + microfilaments (actin).

Membrane Structure (Fluid Mosaic)

• Phospholipid bilayer with hydrophilic heads outside, hydrophobic tails inside.
• Cholesterol embedded for fluidity regulation.
• Integral (transmembrane) and peripheral proteins.
• Selectively permeable; transport via diffusion, facilitated diffusion, active transport, endocytosis/exocytosis.

Prokaryote vs Eukaryote

FAQ

Q: Mitochondria DNA — tested?

Yes, ~1 MCQ per paper. Mitochondria have their own circular DNA (endosymbiotic theory).

Q: Cell cycle phases?

G₁ → S (DNA synthesis) → G₂ → M (mitosis: prophase, metaphase, anaphase, telophase). G₀ = resting.

Q: Centrioles in plant cells?

Absent in higher plants. Common trap MCQ.

Drill our Cell Structure chapter page, then practice past-paper MCQs from our Biology archive.