Question

How is glycogen synthesis and breakdown a) reciprocally regulated to prevent the formation fo a futile cycle? and b) hormonally regulated to increase the supply of available ATP during times of stress?

Answer 1

Synthesis

Glycogen synthesis is, not at all like its breakdown, endergonic—it requires the contribution of energy. Energy for synthesis originates from uridine triphosphate (UTP), which responds with glucose-1-phosphate, framing UDP-glucose, in a response catalyzed by UTP—glucose-1-phosphate uridylyltransferase. Glycogen is integrated from monomers of UDP-glucose at first by the protein glycogenin, which has two tyrosine anchors for the decreasing end of glycogen, since glycogenin is a homodimer. After around eight glucose particles have been added to a tyrosine residue, the catalyst glycogen synthase logically protracts the glycogen chain utilizing UDP-glucose, including ? (1?4)- bonded glucose.

The glycogen branching enzyme catalyzes the exchange of a terminal fragment of six or seven glucose deposits from a nonreducing end to the C-6 hydroxyl gathering of a glucose residue more profound into inside of the glycogen particle. The branching enzyme can follow up on just a branch having no less than 11 residue, and the protein may exchange to a similar glucose chain or contiguous glucose chains.

Breakdown

Glycogen is separated from the nonreducing end of the chain by the enzyme glycogen phosphorylase to deliver monomers of glucose-1-phosphate:

In vivo, phosphorolysis continues toward glycogen breakdown in light of the fact that the proportion of phosphate and glucose-1-phosphate is generally more prominent than 100. Glucose-1-phosphate is then changed over to glucose 6-phosphate (G6P) by phosphoglucomutase. An extraordinary debranching enzyme is expected to expel the ? (1-6) branches in branched glycogen and reshape the chain into a straight polymer. The G-6-P monomers created have three conceivable destinies:

•           G6P can proceed on the glycolysis pathway and be utilized as fuel.

•           G6P can enter the pentose phosphate pathway by means of the catalyst glucose-6-phosphate dehydrogenase to create NADPH and 5-carbon sugars.

•           In the liver and kidney, G6P can be dephosphorylated back to glucose by the chemical glucose 6-phosphatase. This is the last advance in the gluconeogenesis pathway.

Regulation of glycogen metabolism with a learning of both degradation and synthesis.

Glycogen breakdown and synthesis are proportionally directed by a hormone-activated cAMP course acting through protein kinase A. Notwithstanding phosphorylating and enacting phosphorylase kinase, protein kinase A adds a phosphoryl group to glycogen synthase, which prompts a decrease in enzymatic action. This imperative control system keeps glycogen from being synthesis while it is being broken down.

Increase the supply of available ATP during times of stress

Glucose is metabolized into pyruvate through glycolysis in the cytoplasm, and pyruvate is completely oxidized to generate ATP through the TCA cycle and oxidative phosphorylation in the mitochondria. In the fasted state, the liver secretes glucose through both breakdown of glycogen (glycogenolysis) and de novo glucose synthesis (gluconeogenesis). During pronged fasting, hepatic gluconeogenesis is the primary source of endogenous glucose production. Fasting also promotes lipolysis in adipose tissue to release nonesterified fatty acids which are converted into ketone bodies in the liver though mitochondrial ? oxidation and ketogenesis.