Messengers & cAMP
Biology: Cambridge International A Level, topic 14.3.1
Messengers
Control of blood glucose concentration involves both primary and secondary messengers.
Primary messengers
- Primary messengers are messengers that do not enter a cell.
- Primary messengers exert an action on the cell membrane by binding to receptors and triggering a change within the cell.
- This change can be the activation of another molecule (a secondary messenger) or it may initiate a reaction.
- Hormones are examples of primary messengers (e.g. adrenaline and glucagon).
Secondary messengers
- Secondary messengers initiate and coordinate responses that take place inside a cell.
- Secondary messengers are usually activated by the binding of a primary messenger to a cell surface receptor.
- Cyclic AMP (cAMP) is an example of a secondary messenger.
Cyclic AMP
Cyclic AMP (cAMP) is a secondary messenger involved in the control of blood glucose concentration. The steps involved in the response are:
Primary messengers
- Adrenaline or glucagon bind to receptors on the cell membranes of liver cells.
- Adrenaline and glucagon are primary messengers because they do not enter the cell.
Adenylate cyclase
- Binding of adrenaline or glucagon activates an enzyme called adenylate cyclase.
- Adenylate cyclase converts ATP to cyclic AMP (cAMP).
cAMP
- cAMP activates an enzyme called protein kinase A.
- Protein kinase A triggers a cascade of reactions that result in glycogenolysis.
Glycogenolysis
- Glycogenolysis breaks down glycogen into glucose.
Test yourself on Messengers & cAMP
Which of the following are NOT true for primary messengers?
Which of these statements about primary and secondary messengers are true?
What molecule is activated when adrenaline or glucagon binds to receptors on the liver cell membrane?
Which of the following statements about cAMP are true?