Question

In krebs cycle, malate hand over hydrogen to
A. $NAD^+$
B. FAD
C. FMN
D. Oxaloacetate

Answer 1

Hint: Kreb cycle is also known as citric acid cycle, which is found in all aerobic organisms, to release stored energy via oxidation of acetyl-CoA which is derived from carbohydrates, proteins and fats. This citric acid cycle consumes Acetyl-CoA and water and reduces $NAD^+$ to NADH and releases $CO_2$. The NADH is utilized in oxidative phosphorylation.

Complete answer:
Kreb cycle is known form energy production cycle and would take place in mitochondrial matrix of eukaryotic cell while in case of prokaryotes it takes place in cytosol. The amount of energy containing molecules are three NADH, one $FADH2$ and one GTP. It is the key metabolic cycle, which connects the metabolism of fats, protein and carbohydrates.

In the last segment of this kreb cycle, the restoring of oxaloacetic acid by dehydrogenation reaction in which removing of hydrogen pair atoms form malate by the enzyme called malate dehydrogenase. The one proton and two electrons from hydrogen pass to $NAD^+$ molecule to form NADH and $H^+$

Hence, the correct answer is option (A).

Additional information:
> Option B: FAD-
In the Kreb cycle, when succinate is formed from succinyl-CoA, the succinate is converted into fumarate by the help of enzyme succinate dehydrogenase in which FAD is required, where FAD is converted into $FADH2$.

> Option C: FMN-
Flavin mononucleotide is converted into FAD by enzyme FAD pyrophosphorylase with ATP. Flavin mononucleotide is formed by an enzyme called riboflavin. The formation of FAD from FMN, which is utilised in the kreb cycle during conversion of succinate to fumarate.

> Option D: Oxaloacetate-
It is formed in the citric acid cycle as an intermediate. It reacts with acetyl-CoA to create citrate by the help of enzyme citrate synthase.

Note: The citric acid cycle is the series of reaction to produce energy in the form of NADH, FADH, GTP, which is eight step process carried out by the number of enzyme, the end product is formed is oxaloacetate which is further utilize in this reaction to produce energy.