Untitled Quiz

Cell Membrane Structure

• Composed primarily of lipids and proteins.
• The lipid component includes phospholipids, cholesterol, and glycolipids.

Protein Functions

• Essential for various cellular activities including:
  • Transport across the membrane
  • Structural support
  • Communication with other cells
  • Enzymatic activity

Passive Transport

• Movement of substances across the membrane without energy expenditure.
• Includes:
  • Simple diffusion
  • Facilitated diffusion
  • Osmosis

Simple Diffusion

• Kinetic movement of molecules or ions through the lipid bilayer membrane.
• Occurs through intermolecular spaces or membrane openings.
• Rate of diffusion depends on:
  • Concentration gradient
  • Velocity of kinetic motion of molecules
  • Number and sizes of openings in the cell membrane.

Simple Diffusion Through Protein Channels

• Occurs through integral cell membrane proteins, often open pathways.
• Pores provide selective permeability based on size and electrical charge.
• Channels are highly selective for ions.
• Channels have gates, regulated by electrical signals (voltage-gated channels) or chemical binding (ligand-gated channels).

Facilitated Diffusion

• Movement of substances with the aid of a specific carrier protein.
• Used for relatively large organic molecules like glucose and amino acids.

Osmosis

• Net diffusion of water across a membrane due to a water concentration difference.
• Water moves from a region of high water concentration to a region of low water concentration.
• The concentration of water is inversely related to the number of solute particles, regardless of particle size.

Osmotic Pressure

• The pressure required to prevent osmosis.
• Related to the number of particles in solution, not their mass.
• Higher solute concentration = Higher osmotic pressure.

Osmolarity and Osmolality

• Osmolarity: Number of osmoles per liter of solution.
• Osmolality: Number of osmoles per kg of solution.
• Normal osmolarity of body fluids: 290 mosm/L

Isotonic, Hypertonic, and Hypotonic Solutions

• Isotonic solution: Same solute concentration as extracellular fluid.
• Hypertonic solution: Higher solute concentration than extracellular fluid.
• Hypotonic solution: Lower solute concentration than extracellular fluid.

Active transport

• Movement of substances against their concentration gradient, requiring energy.
• Utilizes specific carrier proteins.

Types of Active Transport

• Primary active transport
• Secondary active transport
  • Co-transport (symport)
  • Counter-transport (antiport)

Primary Active Transport

• Sodium-Potassium Pump (Na+/K+ ATPase):
  • Pumps 3 Na+ ions out of the cell and 2 K+ ions into the cell against their concentration gradients.
  • Requires ATP for energy.
  • Maintains the concentration gradient of Na+ and K+, crucial for nerve cell functions and other excitable cells.

Secondary Active Transport

• Uses the energy stored in the concentration gradients created by primary active transport to move other molecules or solutes.
• Two solutes bind to the same transporter protein.
• One solute moves along its concentration gradient, providing energy for the other solute to move against its gradient.

Co-transport (Symport)

• Two solutes move in the same direction.
• Examples: Na+/glucose co-transport, Na+/amino acids co-transport.

Counter-transport (Antiport)

• Two solutes move in opposite directions.
• Examples: Na+/Ca+ counter-transport, Na+/H+ counter-transport.

Endocytosis and Exocytosis

• Mechanisms for transporting large molecules, particles, or fluid droplets across the cell membrane.

Endocytosis

• Bringing substances into the cell.
• Types:
  • Phagocytosis (cell eating): Engulfing large particles like bacteria, damaged cells, tissue debris.
  • Pinocytosis (cell drinking): Transporting proteins, fats, and extracellular fluid.

Exocytosis

• Releasing substances from the cell.
• Membrane-bound vesicles in the cytoplasm fuse with the plasma membrane and release their contents to the extracellular fluid.