Biochemistry of insulin

Question 1

Via what channel does glucose enter the pancreatic beta cells?

Answer 1

GLUT2

Question 2

What two body organs contain gluocokinase?

Answer 2

Pancreas

Liver

Question 3

What is Km?

Answer 3

The substrate concentration at which the reaction rate is half of Vmax

Question 4

Describe the process of secretion of insulin

Answer 4

1. Glucose enters via GLUT2 transporter
2. Glucokinase then phosphorylates glucose and starts off a series of reactions that cause a rise in intracellular ATP.
3. This rise in ATP close the K+/ATP channel and stops the influx of pottassium into the cell.
4. This prevents potassium ions (K+) from leaving the cell by facilitated diffusion, leading to a buildup of potassium ions. As a result, the inside of the cell becomes more positive with respect to the outside, leading to the depolarisation of the cell surface membrane.
5. The depolarisation causes opening of the voltage gated calcium channels which then causes influx of calcium.
6. This cause fusion of preformed insulin granules with the cell membrane and therefore release of insulin.

Question 5

Is the Km of glucokinase low or high for glucose?

Answer 5

Low

Question 6

What drugs act on the K+/ATP channel?

Answer 6

Sulfonylureas such as tolbutamide

Question 7

What happens to pottassium when the K+/ATP channel is closed?

Answer 7

Pottassium can no longer leave the cell leading to a build up on pottassium in the cell. This means that inside the cell is slightly more positive and so causes the membrane to become depolarised.

Question 8

What three amino acids contain hydroxyl groups?

Answer 8

Serine, theonine and Tyrosine

Question 9

What links the alpha and beta subunits of the insulin receptor?

Answer 9

Disulphide bonds

Question 10

What happens int he cell when insulin binds to the insulin receptor in peripheral cells?

Answer 10

Translocation of the GLUT4 channels to the cell membrane to allow influx of glucose into the cell.

Question 11

What happens to the insulin receptor itself when insulin binds to it?

Answer 11

Auto-phosphorylation

Question 12

What do the D cells of the pancreas secrete?

Answer 12

Somatostatin

Question 13

List the metabolic effects on insulin

Answer 13

Inhibits gluconeogenesis
Causes movement of insulin into cells
Increases glycolysis in adipocytes and skeletal muscle cells
Inhibits glycogenolysis

Question 14

What effect does insulin have on glucagon release?

Answer 14

Decreases glucagon release

Question 15

Where are ketone bodies formed?

Answer 15

Liver mitochondria