How many molecules of ${\mathrm{glyceraldehyde}}_3-\mathrm{phosphate}$ ($G_{3}P$) are needed to synthesize one molecule of $\mathrm{glucose}$ during glycolysis?

• A. $2$
• B. $4$
• C. $3$
• D. $1$

Answer: (A)

Verified step by step guidance

1. Understand the role of glyceraldehyde-3-phosphate (G3P) in glycolysis. G3P is an intermediate in the glycolytic pathway, which is crucial for the conversion of glucose into pyruvate.
2. Recall the process of glycolysis, where one molecule of glucose (C₆H₁₂O₆) is broken down into two molecules of pyruvate. During this process, G3P is formed as an intermediate.
3. Consider the steps of glycolysis where glucose is split into two 3-carbon molecules, which are then converted into G3P. This means that for each glucose molecule, two G3P molecules are involved.
4. Recognize that the synthesis of glucose from G3P involves the reverse of glycolysis, known as gluconeogenesis. In this process, two molecules of G3P are required to form one molecule of glucose.
5. Conclude that to synthesize one molecule of glucose, two molecules of glyceraldehyde-3-phosphate are needed, as each G3P contributes three carbon atoms to the six-carbon structure of glucose.