## **Core Concept**
Gluconeogenesis is a metabolic pathway that results in the generation of glucose from certain non-carbohydrate carbon substrates. It is an essential mechanism by which the body maintains blood glucose levels during fasting or when glucose is in short supply. Glycolysis and gluconeogenesis share several enzymes but with different directions of reaction.

## **Why the Correct Answer is Right**
The correct answer, **Pyruvate Carboxylase** is not an enzyme of glycolysis; however, among the enzymes of glycolysis that are used in gluconeogenesis, **Pyruvate Kinase** is not one of them because its step is bypassed. The enzymes of glycolysis that are used in gluconeogenesis with modifications (like change in direction or using different enzymes for the same reaction) include **Hexokinase** (or **Glucokinase** in liver), **Phosphoglucose Isomerase**, **Aldolase**, **Triosephosphate Isomerase**, **Glyceraldehyde-3-phosphate Dehydrogenase**, **Phosphoglycerate Kinase**, **Phosphoglycerate Mutase**, and **Enolase**. However, **Pyruvate Carboxylase** and **PEP Carboxykinase** are unique to gluconeogenesis. Among traditional glycolytic enzymes directly participating, **Glucose-6-phosphatase** is crucial for the final step.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is blank and cannot be evaluated.
- **Option B:** This option is blank and cannot be evaluated.
- **Option C:** This option is blank and cannot be evaluated.
- **Option D:** This option is the correct answer based on the question prompt but seems to be missing details.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **Glucose-6-phosphatase** is an enzyme that is crucial for both gluconeogenesis and glycogenolysis, as it catalyzes the final step in which glucose-6-phosphate is converted to glucose, which can then be released into the bloodstream.

## **Correct Answer:** D. Glucose-6-phosphatase