Question

What is an effect of cAMP-dependent protein kinase (PKA) inactivation of the liver isozyme but not the muscle isozyme? Phosphate from the dephosphorylation of the liver isozyme is used to generate ATP and provide energy for movement. Under stress (fight-or-flight) conditions, the liver can use glycolysis to break down glucose. Glycolysis is inhibited in the liver, but not muscle, when blood sugar is low. Glycogen synthesis is promoted in the liver as an energy store.

Answer 1

The inactivation of cAMP-dependent protein kinase (PKA) in the liver promotes glycogen synthesis by allowing glycogen synthase to remain active, while in muscle it prevents the breakdown of glycogen, supplying a quick energy source during stress conditions.

Step-by-step explanation:

When cAMP-dependent protein kinase (PKA) is inactivated in the liver isozyme but not the muscle isozyme, this affects metabolic processes differently in these tissues. In the liver, PKA inactivation can promote glycogen synthesis as an energy store. This is because the inactivation of PKA leads to a decrease in the phosphorylation of glycogen synthase, the enzyme responsible for creating glycogen from glucose, thereby allowing glycogen synthesis to proceed. Additionally, PKA inactivation in the liver can also halt glycogen breakdown because glycogen phosphorylase, the enzyme responsible for breaking down glycogen into glucose-1-phosphate, requires activation by phosphorylation, which is mediated by PKA when it is active. However, this pathway operates differently in muscle cells where the activation of PKA during stress conditions such as fight-or-flight response leads to an increase in glycogen breakdown to supply energy quickly for muscle contraction and movement.

It is crucial to understand the fate of glucose-1 phosphate (G-1-P) to glucose-6-phosphate (G-6-P) and its roles in glycolysis and gluconeogenesis. G-1-P is converted to G-6-P in glycolysis, which can then be further metabolized for energy production, or in the case of gluconeogenesis, can be used to generate free glucose for release into the circulation. Understanding the dynamics of these biochemical pathways helps explain how the body balances its need for immediate energy versus storage for later use.

Answer 2

Phosphate from the dephosphorylation of the liver isozyme is used to generate ATP and provide energy for movement.

Glycolysis is inhibited in the liver, but not muscle, when blood sugar is low.

Step-by-step explanation:

cAMP-dependent protein kinase (PKA) is a group of enzymes that function in the presence or absence of cyclic AMP (cAMP). They depend on the release of this cAMp to initiate response such as regulation of glucagon, sugar and even lipid metabolism in the body.

Phosphorylation of the cAMP-dependent kinase leads to the inactivation of phosphorylase in the liver thereby inhibiting glycolysis which is the break down of glucose molecules to form energy (ATP) and stimulates glycogenesis which is the break down of glycogen in the liver to form energy. When the blood glucose level reduces, elevated levels of glucagon leads to the increase in the level of cAMP which causes phosphorylation and inactivation of the liver enzyme thus glycolysis and stimulation of gluconeogenesis.

In the muscle cells, the release of cAMP instead causes the stimulation of glycogenolysis by phosphorylating glycogen through phosphorylase kinase and glycolysis and inhibition of glycogenesis by inhibiting glycogen synthase.

cAMP- dependent protein kinase inactivation of the liver isozyme and not the muscle isozyme is to sure rapid supply of energy to the muscle cells for movement and also from the liver through the breakdown of glycogen stored in it. The other two options do not occur by the action of cAMP-dependent protein kinase .