Question

1. Give one example of a mammalian inter-organ metabolic regulator and one example of a cellular metabolic regulator. Briefly describe their functions.

2. Describe how different G protein-coupled receptors can give rise to the synthesis of different 2nd messengers, and name three such G protein-induced 2nd messengers and name their subsequent target.

Answer 1

ANS .(1) One example of inter organ regulator is lactose sugar which move from muscle after glycolysis to liver by blood and get converted to glucose finally via Cori cycle . Similarly other chemicals like amino acid alanine is moved to liver from muscles . Hormones from pituitary moves to other gland to regulate their function like TSH to thyroid gland .

ANS .(2) When hormones or other signal molecules bind to their G protein coupled receptors GTP is hydrolysed activating the protein to start Cascade of activation of membrane bound and free proteins which finally pass signal to genes as G protein coupled receptors cause activate of adenylate cyclase which act as activator in signal transduction . This adenylate cyclase caused conversion of ATP into cyclic AMP which act as second messenger . This further activate various protein kinase leading to phosphorylation reaction .

In another signal transduction where Inositol 1,4,5 phosphate (IP3)is second messenger another type of activation of enzyme phospholipase occurs by G protein . IP3 binds to endoplasmic reticulum calcium channel allowing exit of ions . One more second messenger is Diacyl glycerol (DAG) lipid solubles activate cytoplasmic protein . Some calmodulin proteins also act as second messenger in cell leading to change in calcium ion concentration and other molecular modification .