Cell Structure and Function

Cell Theory

  • All new cells come from the division of preexisting cells.
  • Cells are the smallest unit that perform all vital and physiological functions.

Cell Formation

  • Sperm and ovum unite, then cells multiply and divide to form different types of tissue.
    • Epithelial tissue
    • Connective tissue
    • Muscle tissue
    • Neurological tissue

Extracellular vs. Intracellular Fluid

  • Extracellular Fluid: Fluid outside the cell.
    • Analogy: Stepping outside your house into a thick fluid.
  • Intracellular Fluid: Fluid inside the cell.

Plasma Membrane

  • Separates the inside of the cell from the outside.
  • Disrupting the membrane destroys the cell.
  • Experiment: Attempts to manipulate genetics without viruses by using a magnetic field to pull the cell membrane apart and insert a fine needle.
    • Goal: To extract and implant DNA without disturbing the cell membrane, but currently unsuccessful.

Cytoplasm and Cytosol

  • Cytoplasm: The rich, thick, goopy material inside the cell, mostly made of water.
  • Cytosol: The actual goopy, watery material within the cytoplasm.

Organelles

  • Membranous Organelles: Enclosed in a membrane.
    • Mitochondria
    • Nucleus
    • Endoplasmic Reticulum
    • Golgi Apparatus
    • Lysosomes
    • Peroxisomes
  • Non-Membranous Organelles: Not encased in a fatty acid membrane.
    • Cytoskeleton
    • Microvilli
    • Centrioles
    • Cilia
    • Flagella (only in sperm cells in humans)
    • Ribosomes

Plasma Membrane Details

  • Double phospholipid layer.
  • May have microvilli or cilia on the surface, depending on the cell's location.
    • Cilia in respiratory system: Move debris out of airways, pushing it to the back of the throat to be swallowed.
      • Stomach acid dissolves the debris for the immune system.

Organelles Overview

  • Nucleus: Contains DNA.
  • Golgi Apparatus.
  • Lysosomes and Peroxisomes: Aid in the immune system.
  • Mitochondria: ATP (usable energy) factory.
  • Rough Endoplasmic Reticulum: Has ribosomes attached, giving it a rough appearance.

Cell as a City Analogy

  • Factories: Where things are made, packaged, and shipped.
  • Nuclear Power Plant: ATP factory (mitochondria).

Lipids in Plasma Membrane

  • Phospholipids:
    • Fatty acid tails (hydrophobic).
      • Unsaturated fatty acid: Bent tail.
      • Saturated fatty acid: Straight tail.
    • Phosphate heads (hydrophilic).
  • Double Layer:
    • Heads interact with water inside and outside the cell.
    • Tails face each other, avoiding water.

Cholesterol

  • Stabilizes the cell membrane by packing everything more tightly.
  • Body makes 85-90% of cholesterol; the rest comes from diet.
  • Vegan sources: Coconut oil.
  • Stiffens the membrane, which should be in a semi-fluid state for optimal health.

Fluid Mosaic Model

  • Cell membrane is fluid-like, not completely fluid or solid.
  • Too many saturated fats can make the membrane too hard.

Proteins in Plasma Membrane

  • Protein Channels: Openings allowing substances to move in and out of the cell.
  • Receptors: Allow cells to respond to hormones.
    • Hormones bind to receptors, triggering a signal inside the cell.
  • Peripheral Proteins: Easily removable, may include receptors.

Sugars in Plasma Membrane

  • Glucose chains (polysaccharides) attached to cell membrane
  • Glycoproteins: Proteins with polysaccharides attached.
  • Glycolipids: Lipids attached to sugars.
  • Recognition Molecules: Glycoproteins and sugars that identify cells.
    • Unique to each individual, preventing the immune system from attacking the body's own cells.

Autoimmune Diseases

  • Immune system attacks the body's own cells (e.g., rheumatoid arthritis, lupus).
  • The immune system fails to recognize glycoproteins on cells.
  • Treatment: Medications to suppress the immune system, which can weaken the body's ability to fight infections.

Proteoglycans, Glycoproteins, and Glycolipids

  • Proteoglycans: Carbohydrates with proteins attached.
  • Glycoproteins: Sugar proteins (protein with carbohydrates attached).
  • Glycolipids: Sugar and carbohydrates mixed with lipids.
  • Functions:
    • Cell recognition
    • Binding to extracellular structures
    • Lubrication of cell surfaces

Plasma Membrane Functions

  • Physical isolation.
  • Regulation of exchange with the external environment.
  • Structural support.