Question

Muscle and liver have different roles in the regulation of carbohydrate metabolism. For example, in the fight‑or‑flight response, muscle responds to epinephrine by modulating glucose pathways to achieve rapid ATPATP production. In contrast, in conditions where blood glucose levels fall, liver responds to glucagon by producing glucose for export into the bloodstream. Using the metabolic map as a resource, locate the glucose pathways on the map.

Which pathways are stimulated in muscle by epinephrine?

glycolysis

gluconeogenesis

glycogenolysis

glycogen synthesis

Which pathways are stimulated in liver by glucagon?

glycolysis

glycogen synthesis

glycogenolysis

gluconeogenesis

Which liver enzymes are activated by glucagon?

pyruvate kinase

glucokinase

glycogen phosphorylase

glycogen synthase

fructose 1,6‑bisphosphatase

phosphofructokinase‑1

Which liver enzymes are inhibited by glucagon?

glycogen synthase

pyruvate kinase

fructose 1,6‑bisphosphatase

glucokinase

glycogen phosphorylase

phosphofructokinase‑1

Answer 1

Muscle and liver have different roles in the regulation of carbohydrate metabolism. For example, in the fight‑or‑flight response, muscle responds to epinephrine by modulating glucose pathways to achieve rapid ATPATP production. In contrast, in conditions where blood glucose levels fall, liver responds to glucagon by producing glucose for export into the bloodstream. Using the metabolic map as a resource, locate the glucose pathways on the map.

Which pathways are stimulated in muscle by epinephrine?

Glycolysis (glycolysis pathway substrate is glucose. Its end product is phosphoenol pyruvate and few ATPs if the conditions are anaerobic it goes to lactic acid formation with few more ATP formation. If the condition is aerobic enters TCA cycle for high energy production)

Gluconeogenesis (it is production of glucose from various metabolites in the body like reversal of glycolysis)

Glycogenolysis (i.e. breakdown of glycogen to glucose, it is the property of liver cells where glycogen is stored )

glycogen synthesis (conversion of excess of glucose like post parandial and is property of liver where it is stored)

Which pathways are stimulated in liver by glucagon?

Glycolysis

glycogen synthesis

glycogenolysis (i.e. breakdown of glycogen to glucose, it is the property of liver cells where glycogen is stored. Glucagon activates when the glucose level falls down in the blood stream)

gluconeogenesis (it is production of glucose from various metabolites in the body like reversal of glycolysis)

Which liver enzymes are activated by glucagon?

pyruvate kinase

glucokinase

glycogen phosphorylase (phosphorylated- activated form of this enzyme breaks the glycogen to glucose. Phosphorylation of this enzyme is initiated by kinase in response to glucagon signal transduction )

glycogen synthase

fructose 1,6‑bisphosphatase (Phosphorylation of this enzyme is initiated by kinase in response to glucagon signal transduction. Phospholylation activates the enzyme and converts fructose 1,6 bis phosphate to fructose 6 phosphate which is rate limiting step)

phosphofructokinase‑1 (phosphorylation of this enzyme of glycolysis inhibits its activity and prevents the regulating step of fructose 6 phosphate to fructose 1,6 bisphosphate)

Which liver enzymes are inhibited by glucagon?

glycogen synthase

pyruvate kinase

fructose 1,6‑bisphosphatase

glucokinase

glycogen phosphorylase

phosphofructokinase‑1 (phosphorylation of this enzyme of glycolysis inhibits its activity and prevents the regulating step of fructose 6 phosphate to fructose 1,6 bisphosphate)