# DBT JRF 2020 — Question 127

Exam: DBT JRF 2020 · Section: B · Topic: Biochemistry · Difficulty: Medium

## Question

Sam was investigating impact of lactate dehydrogenase knockout on glycolytic pathway. What will be the net NADH production that he would expect in conversion of Glucose to pyruvate in this case?

## Options

- **A.** 2 NADH
- **B.** 0 NADH
- **C.** 3 NADH
- **D.** 4 NADH

## Answer

Option A

## Explanation

Glycolysis from glucose to pyruvate: the pathway is independent of LDH. NADH production occurs specifically at the GAPDH (glyceraldehyde-3-phosphate dehydrogenase) step: $\text{Glyceraldehyde-3-phosphate} + \text{NAD}^+ + \text{P}_i \rightarrow 1,3\text{-Bisphosphoglycerate} + \text{NADH} + \text{H}^+$ . This occurs TWICE per glucose molecule (since glucose is split into 2 triose phosphates). Net NADH from glycolysis: $1 \text{ glucose} \rightarrow 2 \text{ pyruvate} + 2 \text{ NADH} + 2 \text{ ATP} + 2 \text{ H}^+$ . LDH (lactate dehydrogenase) would normally oxidise NADH back to NAD $^+$ (pyruvate $\rightarrow$ lactate) to regenerate NAD $^+$ for continued glycolysis. In a LDH KNOCKOUT, this regeneration is blocked, but NADH production (at GAPDH) during glycolysis itself still yields 2 NADH per glucose. The question asks specifically about NADH produced in glucose → pyruvate conversion = 2 NADH.

Source: https://mypyqbuddy.com/questions/sam-was-investigating-impact-of-lactate-dehydrogenase-knockout-6a05a8a02adafec470293297