The gene expression of which of the following enzymes is not increased by insulin?
**Core Concept**
Insulin is a hormone that regulates glucose metabolism by stimulating the uptake and storage of glucose in cells. It exerts its effects by activating various signaling pathways that increase the expression of genes involved in glucose metabolism, including glycolysis, glycogen synthesis, and glucose uptake.
**Why the Correct Answer is Right**
Insulin stimulates the expression of enzymes involved in glycolysis, such as hexokinase (glucokinase in the liver), phosphofructokinase-1 (PFK-1), and pyruvate kinase. It also increases the expression of enzymes involved in glycogen synthesis, including glycogen synthase and glycogen branching enzyme. However, insulin does not increase the expression of the enzyme glucose-6-phosphatase, which is involved in gluconeogenesis and glycogenolysis.
**Why Each Wrong Option is Incorrect**
* **Option A:** Hexokinase is indeed stimulated by insulin, which increases glucose uptake in cells.
* **Option B:** Phosphofructokinase-1 is a key enzyme in glycolysis, and its expression is increased by insulin to promote glucose breakdown.
* **Option D:** Glycogen synthase is also stimulated by insulin, which promotes glycogen synthesis in the liver and muscles.
**Clinical Pearl / High-Yield Fact**
Insulin resistance, a hallmark of type 2 diabetes, is characterized by impaired insulin signaling and decreased glucose uptake in muscles. This leads to increased glucose production in the liver, which contributes to hyperglycemia.
**Correct Answer:** D. Glucose-6-phosphatase.