Subcellular Organelles – Quick Recall

Genetic Control of the Cell

  • Nucleus
    • Central, double-membrane “command center” containing DNA (chromatin → chromosomes).
    • Parts:
    • Nucleoplasm – semifluid matrix suspending genetic material.
    • Nuclear envelope – double membrane separating nucleus from cytoplasm.
    • Nuclear pores – regulate RNA/solute traffic.
    • Nucleolus – assembles ribosomal subunits.
  • Ribosomes – sites of protein synthesis from mRNA instructions.
    • Free (in cytosol) → proteins for cytoplasmic use.
    • Bound (attached to rough ER / nuclear envelope) → proteins for membranes, export, or organelles.

Endomembrane System

  • Endoplasmic Reticulum (ER)
    • Rough ER – studded with ribosomes; synthesizes/initially modifies proteins.
    • Smooth ER – no ribosomes; synthesizes lipids, detoxifies, stores Ca$^{2+}$.
  • Golgi Bodies – stack of membranous sacs; receive ER products, finish, sort, and package them into vesicles.
  • Lysosomes – enzyme-filled vesicles for intracellular digestion.
    • Phagocytosis – digest food in vacuoles.
    • Autophagy – recycle worn organelles.
  • Vacuoles – large vesicles for storage & transport.
    • Central vacuole in plants: turgor pressure & bulk storage (water, ions, organic compounds).

Energy Houses

  • Mitochondria – "powerhouse"; site of cellular respiration producing most cellular ATPATP.
    • Present in animal, plant & algal cells; quantity correlates with energy demand.
  • Chloroplasts – photosynthetic organelles of plants/algae; convert solar to chemical energy.
    • Contain chlorophyll; have a three-membrane system (outer, inner, thylakoid).

Other Key Structures

  • Plasma (Cell) Membrane – selective phospholipid bilayer barrier.
  • Cytoplasm – cytosol plus organelles.
  • Cytoskeleton – protein fiber network; structural support, motility, organelle anchoring.
  • Cell Wall – rigid layer (plants, fungi, bacteria); protection, shape, prevents lysis.
  • Centrosome – non-membranous MTOC (microtubule-organizing center).

Membrane-Bound vs. Non-Membrane-Bound

  • Membrane-bound: nucleus, ER, Golgi, lysosome, vacuole, mitochondrion, chloroplast.
  • Non-membrane-bound: ribosome, cytoskeleton, cell wall, centrosome.

Quick Grouping Summary

  • Genetic control: nucleus, ribosomes.
  • Endomembrane: ER (smooth/rough), Golgi bodies, lysosomes, vacuoles (+ peroxisomes).
  • Energy houses: mitochondria, chloroplasts.