Question

Choose the correct answers from the alternatives given :
The citric acid cycle

• A. must occur twice for each glucose molecule metabolised
• B. produces 2 ATP directly from the cycle intermediates
• C. produces 4 carbon dioxide molecules per glucose molecule
• D. all of the above

Answer 1

The correct option is D all of the above

• After glycolysis 2 molecules of 3 carbon pyruvate are formed from one molecule of Glucose.
• These pyruvate molecules then are converted to acetyl coA which enters the kerb cycle or the citric acid cycle
• After one acetyl coA molecule undergoes the cycle 4 molecules of NADH, one molecule of FADH and on molecule of ATP is formed.
• This is the number of the molecules formed from one pyruvate when it undergoes one cycle.
• Therefore one glucose molecule forms 2 pyruvates which means that at the end of the kerb cycle one glucose molecule will form 2 ATP
• Also for the formation of carbon dioxide; 2 molecules of carbon dioxide are formed, first one during the converstion of citric acid to ketoglutaric acid and second during the conversion of ketoglutaric acid to succinic acid. Whixh means that each pyruvic acid gives 2 molecules of carbon dioxide per cycle.
• Therefore one molecule of glucose will give 4 molecules of carbon dioxide as for a glucose molecule to be completed metabolised it has to undergo kerb cycle twice.
• Therefore the answer 'all of the above' is correct.