Uring the signal transduction process, the signal often triggers a signal transduction cascade. For example, an activated receptor activates hundreds of protein A. Each activated protein A activates hundreds of protein B and so on until a cellular response occurs. What purpose does this cascade serve?

The cascade is responsible for  amplification of the signal, so one activated receptor can have a significant response.

Explanation:

Signal transduction is any process occurring within cells that convert one type of signal/stimulus into another type. It is known as cell signalling in which transmission of molecular signals from a cell's exterior to its interior. Signals transmitted by cells must be transmitted effectively into cell to ensure an appropriate response. This step is initiated by cell surface receptors which triggers a biochemical chain os events inside the cell, creating  a response.

Cascades are responsible to relay the signals hence these multisteps pathways can amplify a signal. Hence,The cascade is responsible for  amplification the signal, so one activated receptor can have a significant response.

the sugar-phosphate backbone forms the structural framework of nucleic acids, including dna and rna. this backbone is composed of alternating sugar and phosphate groups, and defines directionality of the molecule.