Signal transduction pathways are series of chemical reactions within a cell that are triggered by signals at its surface, leading to changes inside the cell such as activation of genes or alteration in cellular metabolism.
Receptor: This is a protein molecule that receives and responds to signals or stimuli. It's like the first domino in the chain.
Second Messenger: These molecules relay signals received at receptors on the cell surface to target molecules inside the cell. They're like the middle dominos in our analogy.
Effector Protein: This is a protein capable of performing cellular functions when stimulated by a signal molecule. It's like the last domino that falls, causing an effect.