Muscle glycogen cannot contribute directly to blood glucose

Muscle glycogen cannot contribute directly to blood glucose levels because:

A. muscle glycogen cannot be converted to glucose 6-phosphate.

B. muscle lacks glucose 6-phosphatase.

C. muscle contains no glucokinase.

D. muscle contains no glycogen phosphorylase.

E. muscle lacks phosphoglucoisomerase.

Solution

Answer: B. muscle lacks glucose 6-phosphatase

Reason:

Dephosphorylation of glucose-6-phosphate into the phosphate group & glucose is essential under fasting conditions via gluconeogenesis in the presence of glucose-6-phosphatase enzyme. This enzyme is very low in muscle cells and sometimes it is absent in the muscle tissue therefore, \"phosphorylated glucose-6-phosphate\" cannot cross sarcolemma therefore, abundant glucose levels are lesser from glycogen breakdown via gluconeogenesis or glycogenolysis