Chapter 5 BIO :

1. Proteins, Carbohydrates, Cholesterol, Lipid Bilayer

• Proteins:

  • Integral Proteins: Embedded within the lipid bilayer; act as channels or carriers for substances.

  • Peripheral Proteins: Loosely attached to the surface; involved in signaling or maintaining structure.

• Carbohydrates:

  • Attached to proteins (glycoproteins) or lipids (glycolipids) on the extracellular side.

  • Play a key role in cell-cell recognition, communication, and adhesion.

• Cholesterol:

  • Located between phospholipids in the bilayer.

  • Maintains membrane fluidity by preventing the fatty acid chains from sticking together, especially during temperature changes.

• Lipid Bilayer:

  • Composed of phospholipids with hydrophilic heads (polar) and hydrophobic tails (non-polar).

  • Creates a barrier that separates the internal and external environments of the cell.

2. Define Selectively Permeable

• A selectively permeable membrane allows certain molecules (like water, oxygen, and carbon dioxide) to pass through freely, while restricting larger molecules, ions, or polar substances unless aided by proteins.

3. Fluid Mosaic Model

• Describes the structure of the cell membrane:

  • Fluid: The phospholipids and proteins can move laterally within the layer, giving flexibility.

  • Mosaic: The membrane is a patchwork of different proteins (channels, receptors, enzymes) embedded in or attached to the lipid bilayer.

4. Active Transport vs. Passive Transport

• Active Transport:

  • Moves molecules against their concentration gradient (low to high concentration).

  • Requires energy (ATP).

  • Examples: Sodium-potassium pump, proton pump.

• Passive Transport:

  • Moves molecules down their concentration gradient (high to low concentration).

  • Does not require energy.

  • Examples: Simple diffusion, facilitated diffusion (using channel/carrier proteins), osmosis.

5. What Happens to a Cell in a Hypertonic Solution?

• Hypertonic Solution: The concentration of solutes is higher outside the cell than inside.

  • Water leaves the cell to balance the solute concentration.

  • Animal cells shrink (crenation).

  • Plant cells lose water, and the membrane pulls away from the cell wall (plasmolysis).

6. Define Osmosis vs. Diffusion

• Osmosis:

  • The movement of water across a selectively permeable membrane from an area of lower solute concentration to higher solute concentration.

  • Example: Water moving into a dehydrated cell.

• Diffusion:

  • The movement of molecules (gas, liquid, or solid) from an area of high concentration to low concentration, driven by kinetic energy.

  • Example: Oxygen diffusing into cells and carbon dioxide diffusing out.

7. Endocytosis vs. Exocytosis

• Endocytosis:

  • The process by which cells engulf external substances using vesicles.

  • Types:

    • Phagocytosis: "Cell eating" – large particles like bacteria are engulfed.

    • Pinocytosis: "Cell drinking" – smaller particles or fluids are taken in.

    • Receptor-Mediated Endocytosis: Specific molecules are taken in after binding to cell receptors.

• Exocytosis:

  • The process by which vesicles inside the cell fuse with the cell membrane to release contents outside.

  • Example: The release of neurotransmitters from nerve cells.