Question

1) How does pka (protein kinase a) contribute to different responses. Give three examples.

2) Explain how one signal can promote different responses in different cells. For example, epinephrine causes heart to beat faster while causing liver to release glucose.

Answer 1

1.

Protein Kinase A , PKA are group of enzymes, otherwise known as cAMP dependent protein kinases.
As the name implies that these enzymes depend on cAMP levels in cells. These enzymes have
wide variety of functions in the cell. Expression of this protein varies from cell type and
therefore effects of PKA activation differs from cell type to type.
In adipocytes, epinephrine activates beta adregenic receptors which increases lipolysis.
In myocytes of muscular system, binding of epinephrine activates beta adregenic receptors which
sequesters calcium in sarcoplasmic reticulum.
In cells of kideny, binding of glucagon to glucagon receptors enhances renin secretion.

2.
When a certain protein is activated , the target proteins available in cell varies with tissue type.
This is the reason why different proteins are phosphorylated and activated in different cell types.
This is the reason why epinephrine causes heart to beat faster and same epinephrine causes
liver to release glucose as the target molecules being phosphorylated are different and contributes
for differential effect.