6. Define the term \"second messenger\" and name one. How does a second messenge

Question

6. Define the term "second messenger" and name one. How does a second messenger amplify the signal passing forward along a signal cascade? Does the insulin activate protein kinase cascade involve a second messenger? Explain your answer 7. Given that the insulin receptor is a protein kinase activated by insulin, what does the receptor phosphorylate? Make sure your answer mentions which proteins are phosphorylated, and which amino acid side chains are the phosphate group acceptors. 8. Name one of the downstream enzymes (downstream of the insulin receptor) that is activated by the insulin signal cascade.

Explanation / Answer

1) Secondary messengers are intacellular signalling molecules that that relay signals received at receptors on the cell surface. When receptors interact with a signal at the surface of the cell, the secondary messengers relay this signal to the cytoplasm or nucleus. The concentration of signalling molecules are low in a cell and need amplification to maximize their effects in the cytoplasm. The secondary messengers can amplify a signal and influence the activity of enzymes or genes. Cyclic AMP is an example of secondary messenger.

When membrane receptor transmits a signal to many secondary messengers and each second messenger can generate the transcription of many mRNA chains, then the signal will be amplified by many folds.

In, insulin activated protein kinase cascade, the cell surface receptor activates many G protein molecules. The G protein molecules will activate many adenylyl cyclases and each cyclic AMP produced by adenylyl cyclase will activate protein kinases, which then activates several molecules of an enzyme resulting in quicker production of high levels of product.

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