CELL RESPIRATION
THE KREBS CYCLE
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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4-carbon compound
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2-carbon compound
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pyruvic acid
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NAD+
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Detailed explanation-1: -First, acetyl CoA combines with oxaloacetate, a four-carbon molecule, losing the CoA group and forming the six-carbon molecule citrate. After citrate undergoes a rearrangement step, it undergoes an oxidation reaction, transferring electrons to NAD+ to form NADH and releasing a molecule of carbon dioxide.
Detailed explanation-2: -To start the cycle, an enzyme fuses acetyl CoA and oxaloacetate together so that citric acid is formed (a 2-carbon molecule + a 4-carbon molecule = a 6-carbon molecule!). This is the first molecule that is made in the cycle and is where the cycle gets its name.
Detailed explanation-3: -The Krebs cycle itself actually begins when acetyl-CoA combines with a four-carbon molecule called OAA (oxaloacetate) (see Figure above). This produces citric acid, which has six carbonatoms.
Detailed explanation-4: -Each Acetyl CoA consists of 2 carbon atoms.