Select the statement that correctly distinguishes between relay proteins and second messengers in signal transduction pathways. Select the statement that correctly distinguishes between relay proteins and second messengers in signal transduction pathways.

1-Signal transduction pathways are multistep pathways that include relay proteins and small, nonprotein, water-soluble molecules or ions called second messengers.

2-Relay proteins are the "first messengers," the extracellular signaling molecules that bind to the membrane receptor. The signal transduction pathways are then formed by the second messengers, which are the relay molecules that respond to the first messengers.

3-Signal transduction pathways are multistep pathways in which relay proteins and second messengers alternate