PHGY 209 Transport Mechanism Textbook notes

PHGY 209 Transport Mechanism Textbook notes - PHGY 209...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
PHGY 209 Transport Mechanism Textbook notes September 14. 2008 Diffusion: Movement of molecules from one place to another solely due to random thermal motion. Higher the temperature and lower the molecular mass, faster the movement. Flux is defined as amount of material crossing a surface per unit time. Net flux is defined as the difference between the two fluxes. At equilibrium, net flux = 0. Net flux always go from a region of high concentration to that of low concentration. Net flux concentration temperature molecular mass surface area medium ( faster flux in air than in water due to less collisions) The magnitude of net flux is given by the equation J = net flux P = permeability coefficient (experimentally determined for a particular type of molecule at the particular temperature, it is related to the ease at which a molecule is able to move across the membrane) A = surface area Diffusion rate and distance:
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Collisions prevent molecules from traveling too far. Diffusion time . It would take too long for nutrients from ingestion to diffuse all the way to the cells that need it. Rather, the circulatory system is responsible for rapidly transporting materials via bulk flow. Diffusion instead provides the movement across the short distance between blood and tissue cells. Cells must have a small volume or diffusion will take years to reach to the other side of the cell. Diffusion through membranes: Rate at which a substance diffuse across a membrane is determined by the time it takes for intracellular concentration to reach equilibrium with the extracellular concentration. Membranes act as barriers that considerably slow the diffusion of molecules due to its hydrophobic interior. (A thousand to a million times slower when compared to diffusion across the same thickness of water) Diffusion of ions across membranes: Ions diffusion at a much faster rate than their solubility predicts. Also, different cells have different diffusion rate for ions. (where the diffusion rate for non polar substance is pretty much uniform across all cells). This is due to the existence of integral membrane protein channels. Ion channels have high selectivity for the type of ions that can diffuse through. This selectivity is on channel diameter, polar subunits of the proteins making the pore, and # of water molecules forming the hydration shell around the ion. Ion movement across the channel depends on an electrochemical gradient. This gradient is based on concentration difference and membrane potential. These two factors may work together or with against each other in creating the electrochemical gradient. Ion channels can be opened/closed in a process called channel gating. There are three types of gating: 1) Ligand gating: bind of specific molecules to channel proteins may produce allosteric change. 2)
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 12/25/2008 for the course PHGY PHGY 209 taught by Professor Annwechsler during the Spring '08 term at McGill.

Page1 / 6

PHGY 209 Transport Mechanism Textbook notes - PHGY 209...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online