Hormonal Communication

Question 1

How is insulin secretion controlled in beta cells?

Answer 1

1. An increase in blood glucose concentration causes glucose to enter B cells via a transporter protein
2. Glucose is metabolised in mitochondria, producing ATP
3. ATP binds to ATP-sensitive potassium ion channels, triggering them to close
4. The cell surface membrane depolarises as potassium can’t enter the cell
5. Depolarisation causes calcium ion channels to open
6. Calcium ions enter the cell, triggering secretory vesicles to release insulin via exocytosis

Question 2

Outline the stages of the second messenger model, using the action of adrenaline as an example

Answer 2

1. Adrenaline binds to a complementary receptor on the cell surface membrane of a liver cell
2. The binding of adrenaline causes the receptor to change shape, activating a G protein
3. This activates the enzyme adenylyl cyclase
4. The activated adenyl cyclase converts ATP into cAMP
5. cAMP acts as a second messenger, binding to and activating many protein kinases via phosphorylation, amplifying the signal from adrenaline
6. Protein kinases activate enzymes that catalyse the breakdown of glycogen into glucose