AP BIOLOGY

Detailed explanation-1: -Many signal transduction pathways amplify the initial signal, so that one molecule of ligand can lead to the activation of many molecules of a downstream target. The molecules that relay a signal are often proteins. However, non-protein molecules like ions and phospholipids can also play important roles.

Detailed explanation-2: -Ligand (first messenger): A chemical messenger that binds specifically to one receptor (e.g. proteins, steroids, hormones, neurotransmitters, small organic molecules such as nitric oxide (NO)). Signaling cascade: The interconnection of individual steps in a signaling pathway.

Detailed explanation-3: -Ligands are termed first messengers, while receptors are the signal transducers, which then activate primary effectors. Such effectors are typically proteins and are often linked to second messengers, which can activate secondary effectors, and so on.

Detailed explanation-4: -The signal transduction cascade begins when adenylyl cyclase, a membrane-bound enzyme, is activated by G-protein molecules associated with the adrenergic receptor. Adenylyl cyclase creates multiple cyclic AMP molecules, which fan out and activate protein kinases (PKA, in this example).

Detailed explanation-5: -A ligand is a molecule that binds another specific molecule, in some cases, delivering a signal in the process. Ligands can thus be thought of as signaling molecules. Ligands interact with proteins in target cells, which are cells that are affected by chemical signals; these proteins are also called receptors.