Question

Which of the following statements is most correct regarding the intracellular chemical signals known as "second messengers"?

1) Second messengers act through receptors called K-proteins.
2) Second messengers usually inactivate protein kinase enzymes.
3) Cyclic AMP and calcium may be second messengers.
4) Second messengers usually act to remove nitric oxide (NO) from the cell.

Answer 1

Cyclic AMP (cAMP) and calcium (Ca2+) are established as second messengers. They relay signals inside cells, resulting in the activation of enzymes and subsequent cellular responses.

Step-by-step explanation:

The question concerns the nature of intracellular chemical signals known as "second messengers." Among the statements given, the most correct regarding second messengers is that cyclic AMP (cAMP) and calcium (Ca2+) may be second messengers. These molecules play a crucial role in cell signaling by relaying the signal received by cell surface receptors to target molecules within the cell. Upon the binding of a signaling molecule to a receptor, an enzyme such as adenylyl cyclase or phospholipase C produces second messengers like cAMP or inositol triphosphate (IP3). These second messengers then act to propagate the signal, typically resulting in the activation of enzymes such as cAMP-dependent kinase, which phosphorylates specific residues on proteins, modulating their activity and initiating various cellular responses, including metabolic changes and gene expression.