Week 8 - Transport Proteins and Regulation

Question 1

In what structure do transport proteins work together to transfer glucose from the intestine to the blood stream?

Answer 1

In the intestinal villi. Epithelial cells line the villi; lumen = digested food in this case.

Question 2

What is a lumen?

Answer 2

The inside space of a tubular structure, such as an artery or intestine.

Question 3

What are the 3 surfaces of epithelial cells called and where do they face in the small intestine?

Answer 3

1. Apical surface: faces the lumen
2. Lateral surface: faces the neighbouring epithelial cells
3. Basal surface: faces the blood /extracellular fluid (bottom)

Question 4

What is the basolateral surface?

Answer 4

Another name for the basal and lateral side, as they are similar in properties.

Question 5

How does glucose go from 1. low concentration in the lumen, to high in the cytosol, to 2. low in the extracellular fluid?

Answer 5

1. The apical side of the villi has a sodium/glucose symporter that uses energy from moving the Na to move the glucose. (sodium always kept low inside the cell by Na/K pump; provides energy)
2. GLUT2 uniporter (facilitated diffusion) on the basolateral side moves it outside of the cell

Question 6

What are intestinal epithelial cells transport proteins restricted by?

Answer 6

They are restricted by tight junctions on the lateral side.

Question 7

What is the purpose of tight junctions on the lateral side of epithelial cells?

Answer 7

1. Keep proteins asymmetrical and on their proper sides

2. Keep glucose from getting between the cells; must go THROUGH epithelial cells.

Question 8

What is on the apical membrane of intestinal epithelial cells?

Answer 8

Na+/glucose symporter.

Question 9

What is on the basolateral plasma membrane of intestinal epithelial cells?

Answer 9

GLUT2 uniporter and Na+/K+ pump.

Question 10

If the glucose concentration in the extracellular fluid on the basolateral side is higher than the cytosol of intestinal epithelial cells, which of the following will occur?
A.) Intestinal epithelial cells will be unable to import glucose from the intestinal lumen.
B.) Intestinal epithelial cells will be unable to export glucose to the extracellular fluid.

Answer 10

A.) Intestinal epithelial cells will be unable to import glucose from the intestinal lumen.;
It’s saying there’s a reversed gradient: symporter can still move glucose from high to low on apical side, and Na/K pump still works as long as there’s ATP… Glucose would go back in instead of exporting, and there would be a build up inside the cell

Question 11

What does an ABC transporter (ATPase) do?

Answer 11

It uses ATP to pump out a small molecule (i.e. a protein in cystic fibrosis).

Question 12

How does an F-type transport ATPase work?

Answer 12

It uses the proton (H+) gradient to drive the synthesis of ATP
(i.e. mitochondria, chlloroplasts, bacteria).

Question 13

How does the V-type transport ATPase work?

Answer 13

It uses ATP to pump protons (H+) into organelles (i.e. to acidify the lumen lysosome and plant vacuole).

Question 14

How are the F-type and V-type transport ATPass related?

Answer 14

They are related structurally; the have opposite modes of action. (i.e. F-type = ATP synthase, V-type = H+ pump).

Question 15

What is ATP synthase and how does it produce ATP?

Answer 15

It is an F-type transport ATPase that uses PASSIVE transport and the H+ electrochemical gradient energy to make ATP (like a rotor).

Question 16

What is an H+ pump and how does it work?

Answer 16

It is a V-type transport ATPase that USES ATP to pump H+ against the gradient in ACTIVE transport (in the lysosome membrane).

Question 17

What is membrane potential?

Answer 17

The difference in electrical charge on two sides of the plasma membrane in all cells.

Question 18

What is the importance of membrane potential?

Answer 18

• used by symporters and antiporters to carry out secondary active transport (plants and animals)
• It is used for action potentials in nerve cells

Question 19

What is secondary active transport?

Answer 19

Transport of a molecule against its concentration gradient via the aid of another molecule (most often Na⁺) down its concentration gradient

• Uses ATP indirectly

Question 20

In animal cells, what 2 things contribute to the generation of membrane potential?

Answer 20

1. Potassium leak channels (differences in permeability)

2. Sodium/Potassium pump (unequal concentration gradients)

Question 21

For membrane potential, what is the gradient of Na and K?

Answer 21

• Na+ gradient with a low cytosolic concentration of Na+

- K+ gradient with high cytosolic concentration of K+

Question 22

How are the gradients made and kept for membrane potential?

Answer 22

1. Higher [Na+] on outside of cell
2. Higher [K+] on inside of cell
3. Na+/K+ pump on membrane moves K+ against gradient to inside, and Na+ against gradient to outside .
4. K+ leak channels leak K+ to outside, adding to positive gradient.

Question 23

What is the net result forms the membrane potential (in animal cells)?

Answer 23

• More + on the outside (Na+ and K+)

- More - on the inside (Cl- and fixed anions)