24. Membrane structure

Question 1

Describe membrane permeability?

Answer 1

1. Lipid soluble molecules can move either way through the membrane
2. Movement of the molecules is dependant upon their concentration
3. Large uncharged or polar molecules such as glucose and ions cannot easily cross the membrane.
4. Membranes act as semi-permeable barriers.
5. Transport across them can be passive or active.

Question 2

Describe simple diffusion?

Answer 2

Movement of molecules from an area of high concentration to an area of low concentration.

Question 3

Describe the carrier-mediated mechanism?

Answer 3

Proteins within the membrane act to pass these molecules from one side to the other. This gain is driven by concentration gradient.

Question 4

Describe Uniporter

Answer 4

Uniporter is movement in one direction.

Question 5

Describe symporter transport?

Answer 5

Molecules transported in the same direction. Requires the presence of A and B for transport to occur.

Question 6

Describe antiporter transport?

Answer 6

Molecules transported in opposite directions

Question 7

Describe simple difussion? (5pts)

Answer 7

1. Driven by a concentration gradient
2. Does not require ATP
3. Not specific
4. Slow speed
5. No limit to capacity

Question 8

Describe carrier-mediated diffusion?

Answer 8

1. Driven by a concentration gradient
2. Does not require energy
3. specific
4. Fast
5. Can be saturated

Question 9

What is v max?

Answer 9

The maximum rate transport can take place

Question 10

Describe how glucose is transported via carrier mediated transporters? (3pts)

Answer 10

1. Glucose will bind to the transporter and will undergo a series of conformational changes allowing the glucose to pass across the membrane and into the cell.
2. After the glucose has been released the transporter then returns to original confirmation allowing transport to continue.
3. This continues until the gradient of glucose is diminished. To prevent this from happening cells remove the glucose from the inside of the cell by converting it to another molecule called Glucose-6-phosphate.

Question 11

Describe features of glucose transport? (3pts)

Answer 11

1. Transport of glucose is selective
2. Transport of glucose can be increased by increasing the number of transporters on the cell surface.
3. GLUT4 transporters are increased on muscle and adipocytes by insulin.

Question 12

Summarise Carrier mediated facilitated diffusion? (6pts)

Answer 12

1. Driven by concentration gradient
2. Gradient is maintained by phosphorylation
3. Bidirectional transport
4. Transporters are selective
5. Transporters can be saturated
6. Some transporters are under hormonal regulation.

Question 13

Describe Active transport (4pts)

Answer 13

1. Movement of molecules from an area of low concentration to an area of high concentration against a concentration gradient.
2. Requires ATP
3. Selective
4. Requires integral membrane proteins.

Question 14

Describe sodium dependant glucose transporters SGLUT-1? (4pts)

Answer 14

1. SGLUT-1 increase the uptake of glucose from the gut into the bloodstream by transporting sodium and glucose together.
2. SGLUT-1 will transport glucose when there is sodium present. The driving force for the movement of glucose is the sodium ions.
3. The concentration of sodium ions within the cells is less than that on the outside of the cells creating a concentration gradient.
4. In order for this to continue ATP hydrolysis must take place.

Question 14

Describe sodium dependant glucose transporters SGLUT-1? (4pts)

Answer 14

1. SGLUT-1 increase the uptake of glucose from the gut into the bloodstream by transporting sodium and glucose together.
2. SGLUT-1 will transport glucose when there is sodium present. The driving force for the movement of glucose is the sodium ions.
3. The concentration of sodium ions within the cells is less than that on the outside of the cells creating a concentration gradient.
4. In order for this to continue ATP hydrolysis must take place.

Question 15

Describe cellular Asymmetry? (5pts)

Answer 15

1. In order for glucose to be taken up by the gut and released into the extracellular fluid and into the bloodstream the transporters are asymmetrically distributed.
2. The glucose and sodium co transporters will take up both glucose and sodium.
3. The sodium is then exchanged for potassium using the sodium potassium ATPASE.
4. The sodium is taken from the gut and transported into the extracellular fluid. Glucose concentration will start to rise up and will eventually have a higher concentration than the glucose inside the extracellular fluid.
5. The glucose will be transported across the basal membrane via facilitated diffusion.

Question 16

Describe tight junctions?

Answer 16

Tight junctions prevent redistribution of transport proteins.

Question 17

Describe re-hydration therapy?

Answer 17

Targets the co-transport of glucose and sodium

Question 18

Describe compartmentalisation? (6pts)

Answer 18

1. Intracellular membranes create local environments and separate reactions.
2. This enables electrochemical gradients to be established.
3. This brings enzymes and reactant together or keeps them apart.
4. This separates reactions
5. Enables the local environment to be regulated
6. Proteins have specific signal sequences which target them to specific organelles.

Question 19

Describe the membrane in lysosomes?

Answer 19

Lysosomes have a ph of 4. The aim of the membrane is to allow the difference in ph to be established. The membrane of the lysosomes have membrane pumps within them and these proton pumps will pump hydrogen ions into the lumen of the lysosome. This requires ATP.

Question 20

Describe a carbohydrate signal?

Answer 20

1. Add a carbohydrate signal to the protein (manno signal)
2. The manno signal is then phosphorylated
3. The phosphorylated manno will direct a hydrolytic enzyme to the lysosome.

Question 21

Describe Lysosomal storage disease?

Answer 21

Lysosomal storage disease is for inclusions. Depending on the cell type accumulation of the inclusions can lead to cellular dysfunction.