Explanation of the terms "downstream signaling" and "upstream signaling"?

Question

In molecular biology, what's the meaning of the terms "downstream signaling" and "upstream signaling"? What's the difference between them?

Answer 1

These are terms regarding Signal Transduction, in which a series of events result in the transfer of a signal. Upstream and downstream are used to distinguish which event happens when in relation to each other. SO something that's downstream of Enzyme A, happens after the activation of that enzyme. Something upstream happens first, and may need to happen in order for the next step to occur. So, downstream/upstream are indicators of placement, and also importance, because some events (downstream) can't happen without events that happen first (upstream).

Answer 2

Upstream is before, or happened sometime before. Downstream is after, or happened sometime after. It is the temporal (time) side of the proximal/distal idea of anatomy.