U1-KA3-MEMBRAN PROTEINS- 2)Ion Transport Pumps And Generation Of Ion Gradients

Question 1

How Is an electrochemical (ion )gradient formed and what does it determine

Answer 1

• for a solute carrying a net charge (such as sodium which carries one positive charge), the concentration gradient and electrical potential difference combine to form the electrochemical (ion )gradient
• this determines the direction of the transport of the solute

Question 2

How is electrical potential difference/ membrane potential created

Answer 2

A membrane potential (an electrical potential difference) is created when there is a difference in electrical charge on the two sides do the membrane

Question 3

What is the sodium potassium pump

• what type of transport does it carried out and how
• which ions transported in and which are transported out

Answer 3

• the sodium potassium (Na+/K+ ATPase) is a vital transmembrane transporter protein found in most animal cells.
• the pump does active transport , moving sodium ions (Na+) out of cells and potassium ions (K+) into cells against steep concentration gradients by using energy directly from ATP hydrolysis

Question 4

Ion pumps ,such as the ______-_________ pump ,use energy from the __________ of ATP to establish and maintain ion gradients

Answer 4

Ions pumps ,such as the sodium potassium pump , use energy from the hydrolysis of ATP to establish and maintain ion gradients .

Question 5

The sodium potassium pump has two stable conformational states - explain these

Answer 5

• the sodium potassium pump has two sable conformational states , one with a high affinity for sodium ions inside the cell , the other with a high affinity for potassium ions outside the cell

Question 6

Remember :ion pumps use energy from the hydrolysis of ATP to establish and maintain ion gradients.
- for each ATP hydrolysed (sodium potassium pump)how many ions are transported

Answer 6

• for each ATP hydrolysed , three sodium ions are transported out of the cell (3 Na+ out) and two potassium ions are transported into the cell (2K+ in) to generate the electrochemical gradients (both concentration gradient and an electrical gradient) across the membrane

Question 7

Stages of the sodium - potassium pump

Answer 7

1) the transporter protein has its ion binding sites exposed to the cytoplasm (intracellular) and has a high affinity for sodium ions inside the cell. 3 Na ions bind to the binding sites
2) after sodium ions are attached ,ATP is reduced transferring a phosphate to the transporter. Phosphorylation by ATP causes the conformation of the protein to change
3) the conformational change has its ion binding sites exposed to the outside of the cell (extra cellular). As it has a decreased affinity for the sodium ions , Na ions are released out of the cell.
4) the new conformation has a high affinity for the potassium ions outside the cell , and so two K ions bind to the sites exposed to the outside of the cell. This triggers de phosphorylation - the release of a phosphate group from the protein.
5) the de phosphorylation causes the protein to revert to its original conformation with the binding sites exposed to the cytoplasm.
6) this conformation has a low affinity for potassium ions so the K ions are released into the cell. The transporter protein has a high affinity for sodium ions again so the cycle is back to stage 1 and can repeat.

Question 8

Where is the sodium potassium pump found and what does it account for

Answer 8

The sodium potassium pump is found in most animal cells and it accounts for a high proportion of the basal metabolic rate in many organisms.

Question 9

Why is the sodium potassium pump so important / state functions

Answer 9

• generation and maintaining of ion gradient for resting potential in neurons
• maintains osmotic balance
• glucose transport in the small intestine

Question 10

Explain glucose transport in the small intestine

- how does sodium potassium pump drive active transport of glucose

Answer 10

• in the small intestine, the sodium potassium pump generates a sodium ion gradient across the plasma membrane if intestinal epithelial cells (so that there is always a low concentration of sodium inside the cell) - this then drives the active transport of glucose.
• sodium ions and can enter the cell down their concentration gradient through a glucose symport channel
  -the energy from the flow allows the simultaneous transport of glucose and sodium into the cell
  As sodium ions enter the cell down their concentration gradient , the simultaneous transport of glucose pumps glucose into the cell against its concentration gradient ,from where it can diffuse into the blood.
  Look at HTPpage38

Question 11

What would happen if Na+/K+ ATPases pump was inhibited

Answer 11

• Na conc increases in cell
• K conc decreases in cell
• polarity decreases