Amphibolic Pathway

An amphibolic pathway or a biochemical pathway serves both metabolic processes, catabolism and anabolism. Through Kreb’s cycle, the amphibolic process can be explained at its best.

Cellular respiration is a biochemical process. Usually, through an amphibolic pathway, glucose breaks down and releases energy. Glucose is a common substrate that is present in all carbohydrates and produces energy. Other compounds, such as protein and fat, also produce energy. 

However, as these compounds can’t produce energy directly, they initially convert into simpler forms. For instance, fats present on lysis provide fatty acid and glycerol. Fatty acid transforms into acetyl-CoA and glycerol converts into PGAL or 3-phosphoglyceraldehyde. After the conversion, these substrates can move to the respiratory pathway.

With the help of protease enzymes, proteins convert into different amino acids. Depending on the type, these amino acids create either acetyl-CoA or pyruvates that help in completing the respiration process. These processes prove that respiration is a catabolic process as, during respiration, these complex compounds convert into simpler molecules.

Discuss how a Respiratory Pathway is an Amphibolic Pathway.

In the respiration process, all the complex compounds like protein and fat break down into simpler forms and produce ATP, the fundamental energy molecule of the body. Both these compounds break down into acetyl-CoA, and the respiration process continues. This part of the respiration is termed as catabolism, and the pathway is a catabolic pathway. 

However, respiration not only includes breaking but also forms compounds. When an organism needs protein or fatty acid, the respiratory pathway holds the process, and the produced acetyl-CoA is used to create fatty acids. Hence, this synthesis of fatty acids is an example of anabolism. 

So, from the above discussion, it can be derived that respiration is a sum of both anabolism and catabolism. That concludes that the respiratory pathway is an anabolic pathway.

Kreb’s Cycle or TCA Cycle

Tricarboxylic cycle or TCA cycle is also called the citric acid cycle or Kreb’s cycle. This cycle is a series of different chemical reactions that take place in the mitochondrial matrix. The amphibolic nature of the TCA cycle is noticed while the aerobic organisms release preserved energy via the oxidation process of acetyl-CoA and amino acid synthesis into ATP.

Process of TCA Cycle

As the TCA cycle starts, Acetyl-CoA merges with oxaloacetate, a four-carbon compound, and creates citrate. This citrate is a six-carbon substrate that subsequently converts into citrate isomer. Then, by oxidation, one carbon dioxide molecule releases and leaves a five-carbon a-ketoglutarate behind.

In the next step, through oxidation, the NAD+ is reduced to NADH and releases one carbon dioxide molecule. The other four-carbon molecules pick the CoA and form succinyl CoA, an unstable compound. The entire process is catalysed by a-ketoglutarate dehydrogenase.

After that, a phosphate group replaces the succinyl CoA and helps in the transformation of ATP from ADP. Here, a four-carbon compound called succinate is formed, and later it creates fumarate through oxidation.

The fumarate converts into malate by adding one water molecule. Lastly, by oxidation of malate, one four-carbon compound called oxaloacetate regenerates. Also, one molecule of NADH is produced from NAD+.

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FAQ (Frequently Asked Questions)

1. Why is Kreb’s Cycle Called an Amphibolic Pathway?

Ans. The Kreb’s cycle includes oxidation of acetyl-CoA and the production of fatty acids by synthesis. That means this cycle serves both anabolic and catabolic pathways which proves the amphibolic role of TCA cycle or Kreb’s cycle.

2. Why TCA Cycle is Called Common Metabolic Pathway?

Ans. In the TCA cycle all food compounds such as carbohydrate, protein, and fat release fuel molecules by oxidation and also produce required nutrients by synthesis. Hence, TCA is called a common metabolic pathway.

3. Why is Glycolysis Considered as an Amphibolic Pathway?

Ans. During glycolysis, ATP is produced via a catabolic pathway and cell materials created from intermediates through an anabolic pathway. Thus, glycolysis is an amphibolic pathway.