Transport of Solutes and Water Across Membrane

Based on TBW, what percentage is ICF and ECF? What solutes is the ECF and ICF high in? What are the different type of ECF?

ICF = 66%; ECF = 33%; ECF is high in Na+ and Cl- ( mnemonic= outside is SALTY).

Different types: transvascular (blood, plasma), Interstitial fluid, transcellular (CSF, stomach fluid)

What are the components of the Plasma membrane and its function

fatty acids, choleterol, proteins, carbohydrtates.

Function: Structure, keep stuff from ECF and ICF out of each other, regulation of exchange between environment and comunication

What are the three type of proteins found in/near plasma membrane and what are some of their functions

integral, lipid bound, peripheral

Functions: enzymes, cellular identity, adhesion, attach to cytoskeleton, transport, receptors

What are the four type of membrane channels

pores, channels, carriers, pumps

What is the formula for Fick’s law? What does it describe? Which type of molecules obey this law?

F = P x A x [concentration gradient]; It basically describes the flux of solutes and its direction. non-electrolytes obey this rule

Describe what determines flux for electrolytes

electrochemical gradient

Describe the properties of pores. Give an example. What type of diffusion is this?

always open, some selectivity. Aquaporin

Describe the properties of gated channels. What are some examples of stimuli that triggers the activation/deactivation of these channels

basically pores but needs something to open and/or close it.

Stimuli: ligand binding, teamperature, mechanical, electrical, etc.

Describe the mechanism of carrier protein. What type of diffusion is this? What determines directionality. Relative speed? Give an example.

Carrier proteins are only open to one side at a time. When something binds to it, the gate closes, then a conformational change occur, then the gate opens to the other side.

This is considered passive facilitated diffusion.

Directionality is determined by the gradients.

It is slower than pores/ gated channels.

Example: Glut1,2,3,4

Why do carriers experience the effect of saturation and not pore/gated channels? Draw out the graph of [] of substance vs diffusion rate for ion channels and facilitated diffusion (carrier)

Carriers can only take something one at a time while pores/gated channels can have many many substances in it at one time. Thus, we can imagine the pores/channels as having infinite capability to transport while carriers are extremely limited. Thus, as we increase solute concentration, the number of carriers mediated transport will reach a max. velocity but for pores/channels, the rate of diffusion will continuously increase

Thus: the graph will look like a straight line for pores/channels but carriers will reach an asymptote (their max velocity limited by the # of carriers)

how does insulin affect glut 4 transporters

if high glucose, insulin will facilitate vesicular translocation of glut 4 towards the surface

What is active transportation? What are some examples primary Active Transportation?

the use of ATP to transport

Examples: Na/K+ Pump, H,K - ATPase pump, Ca-ATPase

Describe the Na+ K+ pump

pumps 3 Na+ out and 2 K+ in in exchange for a hydrolysis of one ATP. This is a very important pump for creating membrane potential.

What is the function of Ca pumps? Where do hydrogen ion pumps exist?

the ca pumps is use to maintain the chemical gradient of Ca2+ between ICF and ECF or even between intracellular compartments.

Hydrogen pumps exist in the gastric glands of stomach and the late distal tube and cortical collecting ducts of kidneys

What is secondary active transport? Which ion is usually used as energy? What are the two types of pumps that uses this

the use of the electrochemical gradient to provide energy for transportation. Usually, Na goes down its gradient while allowing another molecule to go against theirs.

Two types: cotransport (symport) [both go same direction]

counter transport (antiport) [they go opposite direction to one another)

Give an example of Na+ Coupled secondary active cotransport. Where is it used?

SGLT 1 and 2 (sodium-coupled glucose uptake). It is used for cotransport of glucose in kidney and across the intestinal epithelium.

What are two ways in which membrane transport could be regulated

by conformational changes of the transport proteins or through transcription to change the # of these proteins

What two things are vesicular transport essential for? which type of molecules is it usually not the primary route for?

macromolecules an receptor-mediated processes. Usually not the route for small solutes

What is the difference between paracellular and transcellular routes? Give examples on how each can occur.

paracellular: between cells; By osmotic and hyrostatic forces; can be selective

Transcellular: something as simple as aquaporin or by coupling of exchangers