Chapter 3 vesicular transport (extra notes)

Carrier Molecules: Proteins that transport cholesterol in the bloodstream.
LDL Molecules: Composed of a monolayer of phospholipids with lipid-soluble contents, allowing for interaction with cholesterol.
Relevance: Understanding these transport mechanisms is crucial for grasping cell membrane functions discussed in class.

Definition: The plasma membrane serves as a barrier separating the interstitial fluid (outside) and cytosol (inside) of the cell.
Composition Variation:
- Similar solute concentrations but different solute types inside and outside of the cell.
- Importance of selective permeability to maintain intracellular conditions.

Example of Electrolytes: Comparison of sodium and potassium levels in interstitial fluid and cytosol.
Gas Concentration: Higher amounts inside the cell compared to the interstitial fluid, emphasizing selective transport across the membrane.
Transmembrane Assistance: Polar molecules (like sodium) require assistance to cross the plasma membrane.

Definition of Tonicity: The relative concentration of solutes in solutions, impacting cell volume and integrity:
- Isotonic: Equal solute concentrations inside and outside; water movement is balanced, maintaining cell volume.
- Hypotonic: Lower solute concentration outside; water enters the cell, potentially causing it to swell or burst.
- Hypertonic: Higher solute concentration outside; water exits the cell, leading to cell shrinkage.

Principle of Osmosis: Water moves from areas of low solute concentration to areas of high solute concentration.
Restoration of Homeostasis: Cells employ mechanisms to stabilize solute concentrations after being placed in varying tonicities.

Passive Transport: Involves the movement of substances (e.g., diffusion, osmosis) without energy.
Active Transport: Requires energy (usually in the form of ATP) to move substances against their concentration gradient.
- Primary Active Transport: Direct use of energy to transport ions (e.g., sodium-potassium pump).
- Secondary Active Transport: Utilizes the ion gradients established by primary active transport for the movement of other substances (like glucose).

Function: Uses ATP to move sodium out and potassium into the cell, crucial for maintaining resting membrane potential.
Mechanism:
- Phosphate group addition (phosphorylation) alters pump shape, driving ions against their gradients.
- Removal of phosphate (dephosphorylation) facilitates potassium entry after initial sodium export.

Characteristics: Defined by the charge difference across the plasma membrane; typically negative inside compared to outside.
Factors Influencing Potential: Differences in ion concentrations, especially sodium and potassium across the membrane cause this electrical state.

Sodium Gradient: Sodium moving back into the cell from a high concentration area can drive the transport of other molecules (like glucose) against their gradients.
Coupled Transport:
- Symport: Both substances move in the same direction.
- Antiport: Substances move in opposite directions, using sodium's energy to facilitate transport.

Endocytosis: The process of bringing materials into the cell through membrane encasement.
- Phagocytosis: Engulfing large particles by cells (e.g., macrophages).
- Receptor-Mediated Endocytosis: Specific uptake of molecules like viruses using receptor proteins.
Exocytosis: Process of expelling materials from the cell, often involving neurotransmitters utilizing vesicle fusion with the plasma membrane.
- V and T snares: Proteins crucial for vesicle fusion during exocytosis.

Transport Types:
- Passive Transport: No energy; simple diffusion & osmosis.
- Active Transport: Requires energy to move against concentration gradients (primary and secondary).
- Vesicular Transport: Bulk movement via endocytosis and exocytosis.
Importance of Homeostasis: All transport mechanisms play a key role in maintaining cellular environment and function.