Question

How many total dehydrogenetaion occur in citric acid cycle :-

• A. One
• B. Two
• C. Three
• D. Four

Answer 1

The correct option is D Four

Krebs cycle is a stepwise cyclic oxidation process in which four dehydrogenation steps and two decarboxylations steps of active acetate group takes place to produce reduced co-enzymes and Carbon Dioxide.

Step 3: Dehydrogenation

Now isocitrate undergoes dehydrogenation in the presence of an enzyme isocitrate dehydrogenase. Mn2+ ion is required for the functioning of enzyme. Hydrogen given out by isocitrate is picked up by NAD+ (Nicotinamide adenine dinucleotide) to form NADH2. After losing hydrogen, isocitrate is changed into oxalosuccinate (6C).

Step 5: Oxidative Decarboxylation

In this step 5-carbon compound, α – Ketoglutarate undergoes simultaneous dehydrogenation and decarboxylation in the presence of enzyme α – ketoglutarate dehydrogenase complex. This enzyme complex contain TPP, Lipoic Acid , Mg2+ and trans – succinylase. NAD+ and CoA are required. The products formed are 4 – carbon compound succinyl CoA, NADH2 and CO2.

Step 7: Dehydrogenation (Oxidation)

In step 7 of Krebs Cycle 4 – Carbon compound Succinate is oxidized to another 4-carbon compound fumarate with the help of enzyme succinate dehydrogenase and hydrogen acceptor FAD (Flavin Adenine Dinucleotide). The enzyme is attached to inner mitochondrial membrane. It contains or non haem iron (Fe–S) protein. This enables the enzyme to get directly linked to electron transport chain.

Step 9: Dehydrogenation (Oxidation)

With the help of enzyme malate dehydrogenase, Malate formed in step 8 is oxidized to oxaloacetate. NAD+ reduced to NADH2.

So the correct option is 'Four'.