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Understanding Cell Membrane Structure and Function

Apr 30, 2025

Lecture Notes: The Cell Membrane and Its Components

Fluid Mosaic Model

  • Describes the cell membrane.
  • Membrane is fluid:
    • Phospholipids and proteins can move freely.
  • Mosaic: Composed of various parts such as:
    • Phospholipids
    • Proteins
    • Glycoproteins
    • Glycolipids
    • Cholesterol

Phospholipids

  • Major component of the cell membrane.
  • Structure:
    • Polar hydrophilic head (loves water).
    • Two nonpolar hydrophobic tails (repel water).
    • Composed of:
      • Phosphate group
      • Two fatty acid chains
      • Glycerol molecule
  • Amphipathic: Molecule with both hydrophilic and hydrophobic parts.

Proteins in the Cell Membrane

  • Peripheral Proteins:
    • Located on exterior or interior surface of the membrane.
    • Can be anchored to cytoskeleton.
    • Function as enzymes or for cell interactions.
  • Integral Proteins:
    • Embedded within the membrane.
    • Transmembrane Proteins: Span across the membrane, are a type of integral protein.
    • Globular Proteins: Spherical proteins, often peripheral.
  • Carrier Proteins: Transport larger molecules like glucose across the membrane.
  • Channel Proteins:
    • Allow ions to pass through (e.g., ion channels for sodium and potassium).
    • Aquaporins: Facilitate water transport.

Glycoproteins & Glycolipids

  • Glycoproteins:
    • Protein attached to a carbohydrate.
    • Involved in immune system functions.
  • Glycolipids:
    • Lipid attached to a carbohydrate.
    • Play roles in cell signaling and interactions.

Cell Membrane Permeability

  • Semi-permeable: Selective about what enters/exits.
  • Small nonpolar molecules (O2, CO2) diffuse easily.
  • Water, though polar, can diffuse slowly.
  • Larger and polar molecules (glucose, ions) require transport proteins.

Cholesterol

  • Maintains membrane fluidity.
  • Structure: Polar (hydroxyl group) and nonpolar regions (fused rings).
  • Acts as a buffer:
    • Decreases fluidity at high temperatures by preventing phospholipids from moving apart.
    • Increases fluidity at low temperatures by preventing phospholipids from packing closely.

Review Questions

  1. Phospholipids:
    • Amphipathic, major components, contain polar heads.
    • False statement: Phospholipids do not contain three fatty acid tails.
  2. Transport Proteins Requirement:
    • Ions (e.g., potassium) and large molecules (e.g., glucose) cannot pass without assistance.
  3. Proteins Spanning Membrane:
    • Transmembrane proteins span the membrane completely.
  4. Fluidity Buffer:
    • Cholesterol maintains membrane fluidity by acting as a buffer.
  5. Increasing Fluidity:
    • Increase in temperature and unsaturated phospholipids increase fluidity.

Matching Practice

  • Semi-permeable: Allows selective passage.
  • Aquaporin: Facilitates water passage.
  • Fluid Mosaic Model: Describes membrane dynamics.
  • Ion Channels: Facilitate ion passage.
  • Cholesterol: Fluidity buffer.
  • Glycoproteins: Cell communication and recognition.
  • Phospholipids: Amphipathic, form bilayer.
  • Glycolipids: Cell signaling.
  • Integral Proteins: Embedded within bilayer.
  • Transmembrane Proteins: Span entire membrane.
  • Carrier Proteins: Transport molecules across.
  • Peripheral Proteins: Lie on the exterior.

This concludes the lecture on the cell membrane. Remember to review these notes to understand the detailed workings of cell membranes and their components.

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