Hey guys,
Could someone please explain the term 'cascade' to me in terms of signal transduction of polar/non-polar signalling molecules, and where does it fit in each event.
Thanks in advance
A signal cascade is the sequence of biochemical reactions in which each reaction causes the next reaction to be possible. It's like a sequence of dominoes tipping each other over. In the transduction of polar ligands, the ligand (usually a hormone I think?) is unable to diffuse across the phospholipid bilayer so it binds to a membrane receptor. The receptor's shape (configuration) then changes - which in turn changes the shape of - and hence activates - a second messenger in the cell's cytosol.
This activated second messenger then activates another second messenger which activates another second messenger which ... . this is what we refer to as a signal transduction cascade. For a non-polar hormone, it diffuses across the phospholipid bilayer and binds to an intracellular receptor - forming a hormone-receptor complex. This complex may then act as a transcription factor - controlling the expression of particular genes. To my knowledge, no cascade occurs in this scenario.
That's only my understanding of it though, and I'd really appreciate if someone could read over it and confirm whether what I'm saying is actually correct!