Cue Column | Notes Column

Cell Theory | Schleiden & Schwann (1838–39): all organisms made of cells; cell = basic unit. Virchow added "Omnis cellula e cellula" (every cell from pre-existing cell).

Prokaryote Basics | No membrane-bound nucleus. Nucleoid region: naked circular DNA. Cell wall: peptidoglycan (murein). Ribosomes: 70S (50S + 30S). Mesosomes: plasma membrane infoldings — assist respiration + division. Plasmids: extrachromosomal circular DNA (antibiotic resistance). Flagella: flagellin protein. Division: binary fission. Size: 1–10 µm.

Eukaryote Basics | True nucleus (double-membraned nuclear envelope + nuclear pores). Chromatin → chromosomes during division. Nucleolus: rRNA synthesis. Cytoplasm: 80S ribosomes (60S + 40S). Size: 10–100 µm.

Endomembrane System | Functional unit: ER → Golgi → Lysosomes → Vacuoles. Rough ER: protein synthesis (ribosomes attached). Smooth ER: lipid synthesis + detox. Golgi: cis face (receives from ER) → trans face (releases vesicles). Lysosomes: hydrolytic enzymes, intracellular digestion. Mnemonic: "Every Girl Loves Vacations."

Semi-Autonomous Organelles | Mitochondria + Chloroplasts: own circular DNA + 70S ribosomes + binary fission. Evidence for endosymbiotic origin. Not part of endomembrane system.

Mitochondria | Double membrane. Inner membrane → cristae (increase SA for oxidative phosphorylation). Matrix: Krebs cycle, circular DNA, 70S ribosomes.

Chloroplast | Double membrane. Thylakoids → grana (light reactions). Stroma $\frac{dark reactions}{Calvin cycle}$, circular DNA, 70S ribosomes.

Plasma Membrane | Fluid Mosaic Model (Singer & Nicolson, 1972). Phospholipid bilayer + integral (transmembrane) + peripheral proteins + cholesterol (animals) + glycoproteins.

Plant Cell Extras | Cell wall (cellulose). Middle lamella (calcium pectate). Large central vacuole (tonoplast). Plastids (chloro-/chromo-/leuco-). Plasmodesmata. NO centrioles (mostly). Cytokinesis: cell plate (centrifugal).

Animal Cell Extras | Centrioles (9-triplet microtubule cylinders → spindle). Lysosomes. Cholesterol in membrane. Cleavage furrow (centripetal). NO plastids, NO large vacuole, NO cell wall.

Cytoskeleton | Microtubules (tubulin) + Microfilaments (actin) + Intermediate filaments. Cilia/flagella: 9+2 tubulin arrangement, dynein motor.

Key Comparisons | Prokaryote flagella: flagellin. Eukaryote flagella: tubulin + 9+2. Prokaryote ribosome: 70S. Eukaryote cytoplasm ribosome: 80S. Mitochondria/chloroplast ribosome: 70S (prokaryotic type).

Cell Structure Diagram

Source: Wikimedia Commons — Animal Cell ultrastructure showing nucleus, ER, Golgi, mitochondria, and other organelles.

Summary

Cells divide into prokaryotic (no nucleus, 70S ribosomes) and eukaryotic (true nucleus, 80S cytoplasmic ribosomes). Eukaryotes have an endomembrane system (ER → Golgi → Lysosomes) and semi-autonomous organelles (mitochondria, chloroplasts). Plasma membrane follows Fluid Mosaic Model (Singer & Nicolson, 1972). Plant cells have cell walls, plastids, vacuoles; animal cells have centrioles and lysosomes.