Lecture 15 - Membrane Transport Flashcards
True or False:
Simple diffusion utilizles proteins
False
diffusion doesn’t utilize proteins in any way
What are the two main things to remember about diffusion?
1) requires a concentration gradient - solute going from a high concentration, down its concentration gradient, to a low concentration
2) the rate of dissolving (disolution) of the solute, affects its solubility –> the more readily it dissolves –> the more soluble it is –> faster it diffuses
Do hydrophobic or hydrophilic solutes more readily diffuse across membrane?
hydrophobic, water doesn’t
*solute dissolves in lipid bilayer to cross
What type of transport is this?
diffusion
What is mediated (facilitated) transport?
How does this affect the rate of movement across membrane?
On the diagram, why does the mediated transport line plateau?
On the diagram, what does it suggest about diffusion?
where a protein is facilitating movement of solute across the membrane (channel)
It increases the rate of movement
because there are only so many proteins that can help, eventually when all proteins are in use, can’t go any faster, rate can’t increase anymore.
there is a linear relationship btw concentration of the solute and rate of movement across the membrane
What do both mediated transport and diffusion have in common?
they require a concentration gradient
What are aquaporins?
How many different family members within the family of aquaporins?
channels with six alpha helical transmembrane domains that allow water and some solutes to traverse the plasma membrane
10 - with tissue specific expression patterns
How does water get through water channel of aquaporin subunit?
What allows pores to be restrictive?
What do they ensure?
give an example
it has pores where water molecules can travel through to get to other side
Several AA residues with side chains extending off alpha helix backbone –> pores have certain size and charge selectivity
only water can get through the pores
Arg = + side chain, repels other + mols
1) What are the three main subunits of the voltage-gated Na+ channel?
2) How many alpha helices are there within the middle subunit?
3) True or False: The alpha helices traverse the membrane
4) Where do Na+ ions pass through?
5) What’s the structure of the channel?
6) True or False: Na+ ions are going against their concentration gradient.
1) alpha, beta 1 and beta 2 subunits
2) the alpha subunit contains 24 alpha helices
3) True
4) through a pore formed by the transmembrane domains
5) 4 groups cluster together to form 1 single pore in the center
6) False - Na+ ions are going down their concentration gradient
1) What is the primary cause of cystic Fibrosis?
2) How is the Cl- transport channel originally set up?
3) What does this mutation result in?
1) a mutation in a Cl- transporter know as CFTR (cystic fibrosis transport regulator)
2) Transports Cl- along as well as water to set up concentration gradient (for Cl-)
3) causes various downstream alterations in fluid movement across the plasma membrane
- without water to accompany it, mucous gets plugged up which impedes cell fn
What is HYPP?
What is it caused by?
What is the result of this defect?
Hyperkalenic periodic paralysis
mutation in skeletal muscle Na+ channel
disturbs channel gating and proper closure
1) What are the two types of membrane transporters?
2) What characteristics do they both share?
3) What are the main differences?
1) Passive transport and active transport
2) saturation kinetics, solute specificity, inhibitable, enzymatic properties (are NOT pores or channels)
3) Passive transport - solutes move DOWN concentration gradient and they DON”T require direct energy expenditure
Active transport - solutes move AGAINST concentration gradient and they REQUIRE energy expenditure
1) What are the 4 main steps of membrane transport?
1) Recognitino - structure of solute and binding site “recognize” each other
2) Transport - protein alters configuration (conformational change)
3) Release - solute is released on opposite side of membrane
4) Recovery - recovers and becomes available to original side (reverts back to original structure)
What are the three types of membrane transporters?
1) Uniport - one solute being transported through membrane
2) Symport - 2 solutes bind at protein and are transported in the SAME direction though membrane
3) Antiport - 2 solutes bind at protein on opposite sides of memrane and are transported in the OPPOSITE direction through membrane
What do symporters and antiporters require to work?
only work if have both solutes binding
Discuss process of Na+/K+ pump
1) ATP is bound to transporter
2) 3 Na+ ions bind to binding site of transporter
3) ATP is hydrolyzed, P gp binds to protein side chain
4) protein changes conformation
5) Na+ ions diffuse out on other side
6) 2 K+ ions bind on other side in binding site
7) P gp comes off
8) protein changes conformation
9) K+ ions leave on opp side
10) ATP binds to transporter
11) protein changes conformation back to original site and is ready for Na+ ions to bind
Describe the process of coupled active transporters
1) Na+ ions are pumped against concentration gradient (using ATP) through active transporter across membrane
2) establishes Na+ gradient of that side
3) Na+ ions travel back through neighboring transporter and the potential E of going down its concentration gradient allows it to bring another solute with it (symporter) - this symporter is a Na+ driven transport\
***1 transporter creates a [] gradient used by a neighboring transporter
