Various cells respond differentially to a second messenger (such as increased cAMP) because they have different: (DNB June – 2008)
- Hormones of drugs require receptors for their action. Some receptors are directly attached to effector molecules and some receptors are coupled to effector molecules and some receptors are couple to effectors by second messengers
- These second messengers are so named because they intervene b/w the original message and the ultimate effect on the cell.
- One of the many sequence of events which follows, when a hormone or a drug combines with receptors coupled to second messengers in given below.
Hormone combines with a receptor
Now receptor changes shape
Combines with Gs protein
Gs protein release GDP and binds GTP
The activates adenylate cyclase
ATP converted to cAMP
Activates protein kinase
Protein kinase phosphorylase serine or threonine
Inactivates or activates enzymes
- Cells respond differentially to a second messenger because the enzymes present in the cell respond differentially to increase or decrease in cAMP For e.g.
i. Increase in cAMP will cause activation of those enzymes which require phsophorylation to get activated where as enzymes which requiring dephospharylation for their active state are inactivated.
- Many students believe that the answer should be 'receptors'
- Now don't get confused. Note that: second messengers respond differentially to a hormone or drug because of receptors but cells respond to second messengers differentially because of different enzymes. Q