Cell Organelles and Compartmentalization Notes

Organelles and Compartmentalization

Organelles

  • Discrete subunits within cells adapted for specific functions.

  • Examples: Nuclei, vesicles, ribosomes, and plasma membrane.

  • Not organelles: Cell wall, cytoskeleton, and cytoplasm.

  • Progress in science allowed for the study of individual organelles using ultracentrifuges and cell fractionation methods.

Nucleus and Cytoplasm Separation

  • Advantage: Separates gene transcription and translation.

  • Allows post-transcriptional modification of mRNA before ribosomes in eukaryotes.

  • In prokaryotes, mRNA may immediately interact with ribosomes due to lack of separation.

Cytoplasmic Compartmentalization

  • Advantages: Concentrates metabolites and enzymes; separates incompatible biochemical processes.

  • Examples: Lysosomes and phagocytic vacuoles.

Mitochondria

  • Adaptations for ATP Production:

    • Double membrane with small intermembrane space.

    • Large surface area of cristae.

    • Compartmentalization of Krebs cycle enzymes in the matrix.

Chloroplast

  • Adaptations for Photosynthesis:

    • Large surface area of thylakoid membranes with photosystems.

    • Small fluid volumes inside thylakoids.

    • Compartmentalization of Calvin cycle enzymes in the stroma.

Nucleus Double Membrane

  • Functional Benefits:

    • Nuclear pores.

    • Breaks into vesicles during mitosis and meiosis.

Ribosomes

  • Free Ribosomes: Synthesize proteins for retention in the cell (cytoplasm).

  • Rough ER Ribosomes: Synthesize proteins for transport within the cell and secretion.

Golgi Apparatus

  • Roles: Processes and secretes proteins.

Vesicles

  • Role: Transport molecules within the cell and facilitate secretion.

  • Clathrin: Protein involved in vesicle formation.

Advantages of Compartmentalization

  • Concentrates metabolites and enzymes.

  • Separates processes.

Mitochondria Structure

  • Inner membrane: Contains ETC and ATP synthase for oxidative phosphorylation.

  • Intermembrane space: Accumulates protons.

  • Cristae: Increase surface area.

  • Matrix: Enzymes and pH suitable for the Krebs cycle.

  • Outer membrane: Contains transport proteins for shuttling pyruvate into mitochondrion

Chloroplast Structure

  • Stroma: Enzymes and pH suitable for the Calvin cycle.

  • Lamella: Connects and separates thylakoid stacks (grana).

  • Thylakoid: ETC and ATP synthase for photophosphorylation.

  • Granum: Increase surface area with small internal volumes to quickly accumulate ions.