Catabolism

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What is Catabolism?

Catabolism meaning is breaking down the complex molecules. It means catabolism is the breakdown of complex substances into their constituent parts (such as amino acids, glucose, and fatty acids), which form substrates for the metabolic pathways.

Metabolism comprises mainly two major parts, where one can be given as anabolism and the other as catabolism. The process of Catabolism is the action of the set of metabolic pathways that break down the molecules into further smaller units that can be either oxidized to release the energy or can be used in the other anabolic reactions.

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Note: The catabolism process involves breaking down large molecules like lipids, polysaccharides, nucleic acids, and proteins into further smaller units such as fatty acids, monosaccharides, amino acids, and, respectively.

Catabolism in Various Organisms

The exact nature of the catabolic reactions varies from organism to organism, and it can be classified according to their energy sources and carbon that can be given below. 

  • Organotrophs - It uses organic sources as an energy source.

  • Lithotrophs - This uses inorganic substrates.

  • Phototroph - It uses sunlight as chemical energy.

Stages of Catabolism

Catabolism can be primarily broken down into 3 stages. These three stages are explained as follows.

Stage 1 - Digestion Stage

The large organic molecules of organic chemistry, such as lipids, proteins, and polysaccharides, are digested into their outside cells' smaller components. This stage acts on cellulose proteins, or starch, that cannot be absorbed by the cells directly.

Stage 2 - Release of energy

After the molecules are broken down, they will be taken up by the cells and converted to yet smaller molecules, generally, acetyl coenzyme A, that releases some energy.

Stage 3 - Storage of Energy

The released energy is then stored by reducing coenzyme nicotinamide adenine dinucleotide into NADH.

This complete process provides the chemical energy that is necessary for the growth of cells and maintenance. A few examples of catabolic processes are the citric acid cycle, glycolysis, the breakdown of muscle protein to use the amino acids as substrates for the breakdown of fat in adipose tissue to fatty acids, gluconeogenesis, and oxidative deamination of neurotransmitters with monoamine oxidase.

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Catabolic Hormones

Various signals control the concept of catabolism, where most of the known signals are molecules and the hormones involved in metabolism itself. Traditionally, endocrinologists have classified various hormones as catabolic or anabolic, based on which part of metabolism they stimulate. 

Since the early 20th century, the so-called classic catabolic hormones known are given as glucagon, cortisol, and adrenaline (and the other catecholamines). In the recent decades, most of the hormones with at least a few catabolic effects have been discovered, such as orexin (also called hypocretin), cytokines, and melatonin.

Protein Catabolism

In molecular biology, protein catabolism can be defined as the breakdown of proteins into simple derivative compounds and amino acids for transport into the cell via the plasma membrane and the polymerization into new proteins, ultimately through ribosomes ribonucleic acids (RNA). Protein catabolism is the breakdown of macromolecules, which essentially is a digestion process.

Protein catabolism is carried out most commonly by a non-specific exo- and endo-proteases. However, some particular proteases are used for protein cleaving for regulatory and for protein trafficking purposes. An example is the subclass of proteolytic enzymes, known as oligopeptidase.

Amino acids that are produced by the catabolism can be directly recycled to produce new proteins and converted into various amino acids or undergo amino acid catabolism, which is to be converted into the other compounds through the Krebs cycle.

Importance of Catabolic Pathways

The catabolic or degradation pathway converts the complex substance to further simpler units.

Their uses can be listed as follows, where it is also given as the catabolic pathways examples.

  • In Glycolysis, 6 carbon glucose is degraded into 3 carbon pyruvate. So, this pyruvate is used in the synthesis of different other components. (catabolism that takes place inside the cell.

  • In the Intestine, the juices act on proteins and convert them into peptone, which is degraded easily to amino acid and absorbed easily into our bloodstream (catabolism in the intestine).

  • Conversion of Glycogen (a branched polymer of glucose) to glucose occurs when we lack the glucose in the blood (catabolism primarily in liver-blood medium).


The importance is not limited only to these two. Besides these, it has numerous counts. Both anabolism and catabolism maintain a constant concentration of nutrients in our body.

Difference between the catabolic and anabolic pathway

Catabolism is the metabolism that breaks complex molecules into simpler ones, whereas anabolism is the metabolic pathways that build complex molecules up from the simpler ones.

A better example of catabolism is the breaking down of glucose into lactic acid. Many of these pathways are exergonic, which means they release energy and generate ATP (Adenosine triphosphate).

Conversion of lactic acid back to the liver's glucose is an anabolic pathway known as gluconeogenesis. It requires an ATP input, as most anabolic pathways do.

FAQ (Frequently Asked Questions)

1. Explain whether Catabolism releases Energy?

Ans: Complex organic molecules can be broken down into smaller molecules via catabolic reactions by releasing the chemical bonds' energy. Not 100% effective are these energy releases (otherwise called conversions). The amount of energy emitted is less than the total amount that the molecule contains.

2. What are Anabolism and Catabolism?

Ans: Anabolism focuses on the development and construction of the organisation of molecules. When we eat food, and the molecules break down in the body for use as energy, catabolism is what occurs. The large and complicated molecules in the body are broken down into smaller and basic ones. An example of catabolism is Glycolysis.

3. Give an Example of a Catabolic Reaction?

Ans: Glycolysis, the degradation of muscle protein, the citric acid cycle to use amino acids as substrates for gluconeogenesis, and the fat degradation in adipose tissue into fatty acids, and the oxidative deamination using monoamine oxidase of neurotransmitters are the instances of the processes of catabolic.

4. List out the Primary difference between Anabolic and Catabolic Reactions?

Ans: Catabolism breaks down the large or complex molecules into smaller molecules, being easier to digest. At the same time, anabolism produces molecules that are necessary for body functioning. Also, the catabolism mechanism releases the steam, and anabolic processes need energy.