JC

Easy Notes – Chapter 3: Cells (with Pictures)

Basics

  • Cell = basic unit of structure & function.
  • Measured in micrometers.
  • Differentiation = cells become specialized.
  • Shape & size relate to function.
  • 3 main parts: Nucleus (control center, DNA), Cytoplasm (organelles in cytosol), Cell membrane (protects, controls entry/exit, signal transduction).

Cell Membrane

  • Made of phospholipid bilayer: Hydrophilic heads outside, Hydrophobic tails inside.
  • Selectively permeable (only certain substances cross).
  • Cholesterol: stabilizes.
  • Proteins: pores, channels, receptors, enzymes, cell ID.
  • Carbs: cell recognition ('self markers').
  • CAMs (cell adhesion molecules): guide cell movement.

Cytoplasm & Organelles

  • Ribosomes: make proteins.
  • Endoplasmic Reticulum (ER): Rough ER = proteins (ribosomes), Smooth ER = lipids.
  • Golgi Apparatus: packages & delivers proteins.
  • Mitochondria: powerhouse, makes ATP.
  • Lysosomes: digest waste ('garbage disposals').
  • Peroxisomes: break down lipids, alcohol, toxins.
  • Cytoskeleton: microfilaments, microtubules → shape & movement.
  • Centrosome/Centrioles: spindle fibers for cell division.
  • Cilia: short, many → move mucus/egg.
  • Flagella: long, one → sperm tail.
  • Nucleus: chromatin (DNA), nucleolus (makes ribosomes).

Transport Across Membrane

  • Passive (no energy/ATP): Diffusion (high→low), Osmosis (water to higher solute), Facilitated diffusion (channels/carriers), Filtration (pressure).
  • Active (requires ATP): Active transport (low→high), Endocytosis (phago=solid, pino=liquid, receptor-mediated=specific), Exocytosis (out of cell), Transcytosis (in→out).

Cell Cycle

  • Interphase: growth & DNA replication.
  • Mitosis: division of nucleus.
    • Prophase: chromosomes appear, nucleus breaks down.
    • Metaphase: chromosomes line up in middle.
    • Anaphase: chromosomes pulled apart.
    • Telophase: nucleus reforms, chromosomes uncoil.
  • Cytokinesis: cytoplasm splits, 2 identical daughter cells.

Cell Division Control

  • Controlled by proteins, hormones, growth factors.
  • Telomeres = 'mitotic clock' → shorten with each division. (represented as ext{telomere length} o ext{shortens with cell cycling})
  • Contact inhibition: cells stop dividing when crowded.
  • Cancer = loss of control → tumor formation.

Practical and conceptual connections

  • The process of diffusion, osmosis, and facilitated diffusion underpins how substances move across membranes without energy.
  • Active transport and endocytosis/exocytosis enable uptake of nutrients and removal of wastes that cannot cross membranes passively.
  • The cell cycle ensures growth, genome integrity, and division; failures lead to cancer or developmental issues.
  • Telomere shortening provides a molecular basis for cellular aging and limits on cellular proliferation; cancer cells often bypass this limit.
  • The organization of organelles reflects division of labor essential for metabolism, growth, and reproduction.

Key terms recap

  • Differentiation, selective permeability, CAMs, cytoskeleton, spindle fibers, chromatin, nucleolus, ATP, lysosome, peroxisome, mitochondrion, ribosome.
  • Endocytosis subtypes: phagocytosis (solid), pinocytosis (liquid), receptor-mediated endocytosis (specific ligands).
  • Cytokinesis as part of cell division yielding two identical daughter cells.
  • Interphase vs mitotic stages (Prophase, Metaphase, Anaphase, Telophase).
  • Telomeres as a cellular clock mechanism.