Membrane Permeability/Pumps Flashcards
What is a semi permeable membrane?
A layer through which only allowed substances can pass
What are examples of hydrophobic molecules? (4) How do they pass through the phospholipid bilayer?
CO2
O2
N2
Benzene
Passive diffusion
What are examples of small polar uncharged molecules? How do they pass through the phospholipid bilayer?
Water
Urea
Glycerol
Passive diffusion
What are examples of large uncharged polar molecules? Can they passively diffuse through the phospholipid bilayer?
Glucose
Sucrose
No
Can ions passively diffuse through the phospholipid bilayer?
No
Can glucose passively diffuse through a phospholipid bilayer?
Yes (but very slowly) so treated as if it cannot
What are permeability coefficients used for in calculations? What scale are they measured in?
To show how long it takes for a molecule to move a certain distance across a bilayer
Logarithmic
What two factors is passive transport across a membrane dependent on?
Permeability
Concentration gradient
Why are models that show membrane transport proteins as ‘rotating’ or ‘flip-flop’ thought to be wrong?
Would require too much energy (thermodynamically unlikely)
How do gated pores transport molecules across a membrane?
Molecule binds —> conformational change —> molecule released on the other side
(Ping pong transport)
What causes voltage gated ion channels to open during membrane depolarisation?
Movement of positive amino acids —> change in conformation (open channel)
An active process will show a ____ value for deltaG
A passive process will show a ____ value for deltaG
+ve (active)
-ve (passive)
Where does the energy come from for active transport to take place?
Some cells spend nearly ___% of their ____ on active transport
Hydrolysis of ATP
50% of their ATP
By the action of which two types of proteins can molecules be carried across a membrane in facilitated diffusion?
Carrier proteins (gated pore model) Channel proteins
Is facilitated diffusion active or passive? Is the movement of molecules by carrier proteins or channels faster?
Passive
Channel proteins are faster
What type of membrane protein does active transport use to transport molecules across a membrane?
Carrier proteins
What is the intracellular [K+] in mM
155mM
What is the intracellular [Na+] in mM
12mM
What is the intracellular [Cl-] in mM?
4.2mM
What is the extracellular [K+] in mM?
4mM
What is the extracellular [Na+] in mM?
145mM
What is the extracellular [Cl-] in mM?
123mM
What is uni-transport? What is an example of a uni-transport protein?
Where only one molecule is transported by the protein at a time
H+ pump
What is co-transport? What two types of co-transport exist? Give an example of a co-transporter protein?
When more than 1 type of ion/molecule are transported per reaction cycle
Anti port (moves two molecules in opposite directions) Symport (moves two molecules in the same direction)
Na/K ATPase pump
What ions does the Na/K ATPase pump move?
3 Na+ out
2 K+ in
What type of ATPase is the Na/K ATPase pump? What does this mean?
P type ATPase
ATP phosphorylates aspartame and produces a phosphoenzyme intermediate
What is the structure of a Na/K ATPase pump?
Has an alpha and a beta sub unit
Alpha subunit = where phosphorylation and transport occurs
Beta sub unit = is gylosylated and directs/anchors the pump to the cell surface
What is responsible for the resting membrane potential? What allows this to occur?
The diffusion of K+ out of the cell through channels
Occurs due to high intracellular [K+] created by the Na/K ATPase pump
What is an example of a symport co-transporter protein?
Na+/glucose co transport in the small intestine and kidney
2Na+ and 1 glucose molecule
How does fluoxetine work at synapses?
Blocks the SERT (serotonin re-uptake channel)
Increasing the action of serotonin
Causes sticky blood as serotonin is taken up by platelets
The Na/K ATPase pump provides the Na+ for…
Absorption of Na+ in epithelia
Action of the NCX (control of calcium levels)
Action of the NHE (pH control)
High intracellular [Ca] is…
Toxic!
What is the difference between the intracellular and extracellular Calcium ion concentrations?
10,000 fold
What molecules are moved by the PMCA? How is it powered?
1 H+ in
1 Ca2+ out
Using ATP
Which molecules are moved by the NCX? How is it powered?
3Na in
1Ca out
Secondary active transport
What molecules are moved by the SERCA? How is it powered?
Ca in
H+ out
Using ATP
Why is the SERCA not a pump? What type of transporter is it?
It is not on the plasma membrane
Primary active transporter
What is the difference in capacity and affinity of NCX and PMCA?
The NCX has a low affinity, high capacity
The PMCA has a high affinity, low capacity
What does depolarisation do to the NCX?
Reverses it
What 2 transporters are acid extruders and help to control cell pH?
NHE
NBC (sodium bicarbonate cotransporter)
What transporter is a base extruder and helps control cell pH? Which ions are moved at this protein?
AE (anion exchanger)
HCO3- out
Cl- in
acidifies the cell
Which ions are moved at the NHE and NBC respectively?
H+ out, Na+ in
HCO3- in, Na+ in
H+ out, Cl- out
Alkalinises the cell
Which drug inhibits the NHE?
Amiloride
The exchangers/transporters that help control cell pH are also important in regulating…
Cell volume
Cell volume is regulated by the movement of osmotically active ions such as…
How many water molecules does each ion bring with it?
Na+, K+, Cl-
6
A shrinking cell will ___________ ions
Influx
A swelling cell will ________ ions
Extrude
Where are bicarbonate ions reabsorbed in the kidney?
What is it important in the body for?
The proximal tubule
Ph buffering
Where is Na+ reabsorbed in the kidneys?
Cortical collecting duct
Distal convoluted tubule
Thick ascending limb
Which transporter helps in the reabsorption of Na+ in the thick ascending limb?
NKCC2
Na/K dichloride cotransporter
What drugs can be used for people with mild hypertension? What transporter do they work on?
Loop diuretics (e.g furosemide)
Block NKCC2
Less sodium and therefore water reabsorbed
