In the transition from a well-fed to a fasting state, which enzyme in liver cells is most likely to decrease in amount?
A) PEP carboxykinase
B) acetyl-CoA carboxylase
C) pyruvate carboxylase
D) glucose-6-phosphate phosphatase
E) glycogen phosphorylase

Question

Quizplus · Accepted Answer

Acetyl-CoA carboxylase is the enzyme that catalyzes the production of malonyl-CoA, which is a necessary precursor for fatty acid synthesis. During fasting, the body switches from using glucose as its primary fuel source to using stored fat. As a result, acetyl-CoA carboxylase activity decreases in order to reduce fatty acid synthesis and promote the breakdown of stored fat. The other enzymes listed are involved in gluconeogenesis (PEP carboxykinase, pyruvate carboxylase, glucose-6-phosphate phosphatase) or glycogen breakdown (glycogen phosphorylase), which would be upregulated during fasting.

In the Transition from a Well-Fed to a Fasting State