This is the answer to why is the citric acid cycle a cyclic pathway rather than a linear pathway?
Why is the citric acid cycle a cyclic pathway rather than a linear pathway?
- Redox reactions that simultaneously produce CO2 and NADH occur only in cyclic processes.
- More ATP is produced per CO2 released in cyclic processes than in linear processes.
- Cyclic processes, such as the citric acid cycle, require a different mechanism of ATP synthesis than linear processes, such as glycolysis.
- It is easier to remove electrons and produce CO2 from compounds with three or more carbon atoms than from a two-carbon compound such as acetyl CoA.
The correct answer about why is the citric acid cycle a cyclic pathway rather than a linear pathway is below.
Related info
The citric acid cycle starts with a two-carbon acetyl group, which in this case comes from pyruvate produced by the glycolytic process. The three-carbon pyruvate reacts with coenzyme A, transferring the two-carbon acetyl group to coenzyme A, and the other carbon atom is released as carbon dioxide.
The citric acid cycle begins with a two-carbon acetyl group, and this acetyl group combines with a molecule called coenzyme A to form acetyl coenzyme A. Acetyl coenzyme A comes from pyruvate, which is produced by glycolysis and is a product of glucose cleavage. Pyruvate has three carbons in its molecular structure, and when it reacts with coenzyme A, two carbon chain groups are transferred to coenzyme A, and the remaining one is released as carbon dioxide.
The citric acid cycle is also called the tricarboxylic acid cycle. This is because the acetyl group combines with the four-carbon compound oxaloacetate to form the six-carbon citric acid. Citric acid undergoes a series of reactions – oxidation and tautomerization. The intermediates in this process are mainly various carboxylic acids. In fact, there are more than three, just three main ones. In this process, two carbon atoms are dissociated successively to produce carbon dioxide, and finally oxaloacetate is produced again, forming a cycle. So oxaloacetate is the catalyst!
The citric acid cycle takes place in the organelle mitochondria. Its reaction material, pyruvate, is produced in the cytoplasm by glycolysis, a step that does not require oxygen.
Pyruvate is then transferred to the mitochondria for oxidation, the first step in aerobic respiration. In higher organisms, aerobic respiration provides most of the energy to our body. If there is not enough oxygen, pyruvate is converted to ethanol or lactate in the cytoplasm, which is called anaerobic respiration.
For example, in brewer’s yeast or lactic acid bacteria, or in muscles that are sore from strenuous exercise because there is not enough blood to oxygenate them.
So brewer’s yeast and lactic acid bacteria can ferment and produce alcohol or yogurt when there is no oxygen, and lactic acid is produced in muscles that feel sore from strenuous exercise because the blood does not have enough oxygen to supply it. Anaerobic respiration provides not only less energy, but the ethanol or lactic acid produced is toxic to animals and plants.
Some of the same enzymes and intermediates are present in the glyoxylate cycle and the tricarboxylic acid cycle. However, they are two different metabolic pathways. The glyoxylate cycle takes place in the glyoxysome and is a reaction process closely related to the conversion of fats to sugars.
The tricarboxylic acid cycle, on the other hand, takes place in the mitochondria and is a process closely related to the complete oxidative decarboxylation of sugars.
Correct Answer
The correct answer to Why is the citric acid cycle a cyclic pathway rather than a linear pathway?
- D. It is easier to remove electrons and produce CO2 from compounds with three or more carbon atoms than from a two-carbon compound such as acetyl CoA.
In the oxidation of acetyl COA by acrylates, one carbon atom is released as carbon dioxide. However, the oxidation of carbon dioxide by the remaining two carbon atoms (acetic acid) requires a complex eight-step pathway – the citric acid cycle.
Therefore, the citric acid cycle a cyclic pathway rather than a linear pathway.
