Question

Which one of the following is a 4C compound?
(a) Oxaloacetic acid
(b) Pyruvic acid
(c) Citric acid
(d) RUBP

Answer 1

Aerobic respiration in plants first in the cytosol where pyruvic acid forms, this pyruvic acid then enters into mitochondria to initiate further steps of respiration. In respiration, ATP plays a major role in the liberation of energy.

Complete Answer:
Oxaloacetic acid is a 4C compound that takes part in the tricarboxylic acid cycle. The Kreb cycle was first discovered by Sir Hans Krebs in 1937. This cycle is also named a Citric acid cycle or Tricarboxylic acid cycle. This cycle starts with the entry of acetyl CoA. Acetyl CoA is a 2C compound combined with a 4C compound of oxaloacetate in presence of enzyme citrate synthase, this leads to the production of 6C compound dicarboxylic or citric acid. Citrate then undergo reorganization to form 6C compound cis-isonate in presence of aconitase. Cis-aconitase reorganizes into 6C isocitrate with the presence of water. Dehydrogenation of isocitrate from oxalosuccinate in presence of enzyme isocitrate dehydrogenase. Oxalosuccinate further decarboxylates to form 5C alpha-ketoglutarate in presence of enzyme decarboxylase. Alpha-ketoglutarate dehydrogenase and decarboxylated to form 4C succinyl CoA by enzyme alpha-ketoglutarate dehydrogenase. Succinyl CoA breaks succinate and CoA in presence of enzyme succinyl thiokinase. Succinate by dehydrogenation from 4C compound fumarate with enzyme succinate dehydrogenase. Fumarate change into 4C compound malate in presence of fumarate. Malate further dehydrogenated in presence of enzyme malate dehydrogenase to form 4C oxaloacetate. Oxaloacetate picks another molecule of active acetate to repeat the cycle. From each molecule of glucose 24 ATP molecules are formed in the citric acid cycle.

So, the correct answer is ‘Oxaloacetic acid’.

Note: In aerobic respiration net gain of 38 ATP molecules take place from one molecule of glucose. This type of respiration takes place in aerobic prokaryotes, heart, liver, and kidney cells of eukaryotes. One ATP molecule liberates 34kJ of energy so a total of 1292 kJ of ATP liberated during the breakdown of one molecule of glucose.