L8: Cell Membranes & Membrane Transport Flashcards
What barriers do biological membranes have?
Selective permeable
What do the selective permeable biological membranes block?
Passage of almost all water soluble molecules
What molecules can freely move through the bilayer?
Small, uncharged or hydrophobic molecules by simple diffusion down concentration gradients
What do charged polar molecules require to move across the membrane?
Specialist proteins (pumps, transporters etc.)
What molecules can permeate across the lipid bilayer?
Hydrophobic molecules, small uncharged polar molecules
Is the concentration of Na+ ions higher on the outside or inside of cells?
Outside
Is the concentration of K+ ions higher on the inside or outside of the cell?
Inside
Is the concentration of Cl- higher on the inside or outside of cells?
Outside
Define Simple/Passive diffusion
A molecule dissolves in the phospholipid bilayer, diffuses across and moves along the concentration gradient
What does the rate of diffusion depend on?
Octonal/water PARTITION COEFFICIENT (Kow) of the solute
What is Kow?
Equilibrium constant for partitioning of a molecule between oil (octanol) and water
If the value of Kow is higher what does it mean in terms of lipid?
More lipid soluble it is
What are transmembrane movement of ions & hydrophilic molecules mediated by?
Proteins
2 ways solutes can cross biomembranes
1) Passive diffusion
2) Active transport
Why are ion channels gated?
Enables the generation of action potential
Why do facilitated diffusion involve a conformational change in selective carrier protein?
Allow molecule to pass through the membrane & be released on the other side
Define uniport transport
When a particular type of molecule moves across a membrane, through carrier protein independently
Define symport transport
2 kinds of molecules move in the same direction while diffusing through carrier proteins
Define antiport transport
Mechanism for the couple transportation of 2 different molecules/ions passing through a membrane in opposite directions
What is a coupled transport?
Transport system where 1 molecule/ion moves down an electrochemical gradient linked to another molecule in the same/opposite direction
Which 2 transports are part of coupled transport?
Symport & antiport
What is the transporter affinity for substrate given by?
Km
What does primary active transport use?
ATP
What does secondary active transport use?
An electrochemical gradient
Define active transport
Movement of molecules against the concentration gradient, requiring energy
Where does Na+/K+ ATPase function in?
Plasma membrane
Where does H+ - ATPase function in?
Lysosomal membrane
Where does Ca2+ - ATPase function in?
Plasma membrane/ ER/SR
STEP 1 of functioning of Na+/K+ ATPase
1) Na+ binds to intracellular site
2) This triggers an AUTOPHOSPHORYLATION of the pump
What does phosphorylation cause?
A conformational change to release Na+ to the outside & exposes a K+ binding site
What does binding of K+ trigger?
A dephosphorylation of the pump
What happens after the K+ binding site is exposed?
Pump returns to original conformation & K+ is discharged into the interior of the cell
Role of Oubain
Inhibits the Na+/K+ ATPase by preventing K+ from binding
Why is SGLUT 1 important?
Intestinal epithelial cells for absorption of dietary glucose
Why is SGLUT 2 important?
Epithelial cells in proximal tubules of kidney for reabsorption of glucose from primary urine
