Question

-Trace the general mechanism by which a signal transduction pathway occurs (i.e. from signaling molecule to response) Describe the two ways in which signaling proteins act as molecular switches -Which amino acid residues do kinases typically add phosphate groups? Distinguish between the two types of G proteins -What proteins regulate GTP-binding protein (G proteins) in terms of activation and inactivation? - Distinguish between the three main classes of cell surface receptors.

Answer 1

GENERAL MECHANISM OF SIGNAL TRANSDUCTION PATHWAY:-

1. During signal transduction, an extracellular molecular signal is transmitted to the cell interior by means of a structure present on the surface or more specifically the cell membrane which is termed as the cell receptor.
2. The response can be either in activation of a cell signalling cascade composed of several proteins that ultimately generates a response by activating the transcription of a gene to initiate protein synthesis and lead to an expression.
3. In other case, there will be change in membrane potentials leading to either inflow or outflow of charged ions to initiate a response.
4. Once the receptor is activated, it can lead to activation of pathway composed of intrinsic enzymes or lead to activation of intrinsic signalling molecules.
5. Receptors include the enzyme-linked receptors which are associated with enzyme activity for their mechanism. Other include the Transmembrane receptors such as G-protein coupled receptors as can be seen in the glycogen metabolism pathway.
6. Receptors can be either membrane bound or suspended in cytoplasm.
7. The signalling cascade mechanism is receptor specific and is associated with amplification of the signals with respect to he intracellular enzymes which finally lead to an appropriate and precise physiological response.
8. Signal transduction pathway includes altering the nature of the enzymes or proteins by means of addition of phosphates that regulate the activity of the enzymes in the transduction pathway. So, there is an effective control over the entire process.
9. Apart from this, there are intracellular messengers like cAMP, nitric oxide, Ca2+ ions which support specific pathways.
10. So, in general, receptors activate the secondary messengers leading to simultaneous activation of enzymes in signalling cascade leading to a response against the signal.