Question

1. All signaling begins with the binding a soluble ligand to a receptor on the exterior cell surface.

True or False

2. Signaling occurs in the absence of any use of energy.

True or False.

3. Name one cellular response controlled by a signaling cascade initiated by an extracellular signaling molecule.

Answer 1

1. True

2. False

3. Epinephrine binds to epinephrine receptor --> Activates Adenylyl cyclase --> converts ATP into cAMP --> activates glycogen phosphorylase enzyme by phosphorylating --> activated enzyme breaks down glycogen into glucose molecules.  

Explanation:

1. Signal transduction cascade plays a critical role in regulating various physiological function in the cell. Cell signalling pathway vary based on types of signal, receptors, and its complexity. However, the signal is triggered once the ligand binds to the receptor.

2. Cell signalling molecules are diverse in nature such as lipids, peptide molecules, polysaccharides, peptidoglycans and nucleic acids. Depending upon the type of signal molecules, their transportation across the membrane may be active or passive, however, further cascade needs at least minimal amount of energy to proceed.

3. Signal pathway plays critical role in various cellular functions including cellular metabolism. When the blood glucose levels are low, adrenalin hormone is secreted, which binds to the epinephrine receptor and pass across the membrane. Epinephrine activates adenylyl cyclase, which inturn converts ATP into cyclic AMP. cAMP phosphorylates 'glycogen phosphorylase' enzyme and there by activates it. Activated enzyme breakdown glycogen into free glucose units into blood stream.