Difference Between Catabolism and Metabolism

Main Difference – Catabolism vs Metabolism

Catabolism and metabolism refer to a collection of biochemical reactions, which occur in the body. Catabolism is the set of biochemical reactions, which are involved in the breaking down of complex molecules in the body into small units. Energy is released during the process of catabolism, which can be readily used in other cellular processes. Metabolism is the whole set of biochemical reactions that occur inside an organism, including catabolism. Anabolism is also included in the metabolism. The main difference between catabolism and metabolism is that catabolism consists of destructive biochemical reactions which occur in the organism whereas metabolism consists of the whole set of biochemical reactions in the organism, which can be either constructive or destructive.

This article explores,

1. What is Catabolism
     – Definition, Processes, Stages, Function
2. What is Metabolism
     – Definition, Processes, Stages, Function
3. What is the difference between Catabolism and Metabolism

Difference Between Catabolism and Metabolism - Comparison Summary

What is Catabolism

The set of reactions which breaks down complex molecules into small units is referred to as catabolism. Catabolism is a destructive process. Catabolic reactions release heat as well as energy in the form of ATP. Thus, these reactions are considered as exergonic processes. The small units of molecules produced in the catabolism can be either used to release energy by oxidation or as precursors in other anabolic reactions. Catabolic reactions are considered to produce ATP energy required by the anabolic reactions.

During catabolism, waste products like urea, ammonia, lactic acid, acetic acid and carbon dioxide are also produced. Many hormones such as adrenaline, cortisol, and glucagon are also involved in this process.

During digestion, complex macromolecules like starch, fats, and proteins from the diet are taken up and broken down into small units like monosaccharides, fatty acids, and amino acids, respectively by digestive enzymes. These monosaccharides are then used in the glycolysis to produce acetyl-CoA. This acetyl-CoA is used in the citric acid cycle, generating NAD+. ATP is produced from NAD+ by going through the electron transport chain during oxidative phosphorylation. Catabolism of proteins, polysaccharides, and fats are shown in figure 1.

Main Difference - Catabolism vs Metabolism

Figure 1: An overview of protein, polysaccharides and fats catabolism

Fatty acids are used to produce acetyl-CoA by beta oxidation. Amino acids are either reused in the synthesis of proteins or oxidized into urea in the urea cycle.

Depending on the utilization of organic compounds either as the carbon source or electron donor, organisms are classified as heterotrophs and organotrophs, respectively. Monosaccharides like intermediately complex organic molecules are broken down by heterotrophs in order to generate the energy required for the cellular processes. Organic molecules are broken down by organotrophs in order to produce electrons, which can be used in their electron transport chain, generating ATP energy.

What is Metabolism

The whole set of biochemical reactions occurring in the body is collectively referred to as metabolism. Three major phases are found in metabolism. First, during catabolism, carbohydrates, proteins, fats and nucleic acids in food are broken down into their small monomer units and nitrogenous wastes are eliminated. Secondly, the resultant monomers like glucose are used as substrates in the cellular respiration by generating energy. Thirdly, during anabolism, small monomer units are polymerized into complex molecules like polypeptides, lipids polysaccharides, and nucleic acids. Collectively, these biochemical reactions affect organism’s growth, development, maintenance of structures, reproduction and response to the outside environment.

Metabolism takes place through metabolic pathways. This means, one chemical compound is converted into its end product of the pathway through a series of biochemical reactions. Each biochemical reaction is catalyzed by unique enzymes. Through the presence of enzymes to catalyze each reaction, these reactions can be regulated in such a way to achieve the required energy by the organism. On the other hand, these enzyme-catalyzed reactions, which require energy are coupled with spontaneous reactions, which release the energy. The rate of the metabolism depends on the amount of food taken by the organism. The connection between metabolic pathways is shown in figure 2.

Difference Between Catabolism and Metabolism

Figure 2: Connection between metabolic pathways

Difference Between Catabolism and Metabolism


Catabolism: The set of biochemical reactions involved in the energy releasing processes in organisms is referred to as catabolism.

Metabolism: The whole set of biochemical reactions in the body are referred to as metabolism.


Catabolism: Catabolism includes the destructive reactions in the body.

Metabolism: Metabolism includes both constructive and destructive reactions in the body.


Catabolism: Releasing energy from metabolism powers the cellular processes and heats the body while allowing the movements of muscles.

Metabolism: Metabolism is important for growth, development, and maintenance of cellular structures and response to the environment.

Energy Form

Catabolism: Reactions are involved in both energy releasing and storing processes.

Metabolism: Potential energy is released as kinetic energy during catabolism.


Catabolism: Catabolism is an exergonic reaction.

Metabolism: Metabolism consists of both endergonic and exergonic reactions.

Oxygen Utilization

Catabolism: Catabolism is aerobic, utilizes oxygen for the process.

Metabolism: Metabolism consists of both aerobic and anaerobic reactions.


Catabolism: Hormones such as adrenaline, cortisol, glucagon and cytokines are involved in the catabolism.

Metabolism: Anabolic hormones such as estrogen, testosterone, growth hormone and insulin and catabolic hormones are involved in the metabolism.

Effect on the Body

Catabolism: Catabolism burns fat and calories. It uses up the stored food in order to generate energy.

Metabolism: Metabolism allows organism’s growth, development, maintenance of structure, reproduction and response to the outside environment.


Catabolism: Catabolism is functional during bodily activities.

Metabolism: Metabolism is functional at both at resting or sleeping and body activities.

Energy Conversion

Catabolism: Potential energy is converted into kinetic energy during catabolism.

Metabolism: Metabolism is an interconversion between potential and kinetic energy.


Catabolism: Catabolism occurs during cellular respiration, digestion and excretion.

Metabolism: Metabolism occurs during photosynthesis in plants, protein synthesis, glycogen synthesis, digestion, respiration, and excretion.


Catabolism: Anabolic process such as photosynthesis and catabolic processes such as cellular respiration are examples.

Metabolism: Digestion, cellular respiration, and excretion are examples for the catabolic processes.


Catabolism and metabolism are terms which collectively describe biochemical reactions inside the body. Metabolism refers to the whole set of biochemical reactions in the body. It includes both catabolism and anabolism which maintain all the features which create an organism. Metabolism affects an organism’s growth, development, reproduction and response to the outside environment. Catabolism includes the biochemical reactions which break down complex molecules into their small units. The main difference between catabolism and metabolism is their relationship between them.   

1.”Metabolism.” Wikipedia. Wikimedia Foundation, 12 Mar. 2017. Web. 16 Mar. 2017.

Image Courtesy:
1.”Catabolism schematic” By Tim Vickers, vectorized by Fvasconcellos – w:Image:Catabolism.png (Public Domain) via
2.”Metabolism pathways (partly labeled)” By Fred the Oyster (CC BY-SA 4.0) via

About the Author: Lakna

Lakna, a graduate in Molecular Biology & Biochemistry, is a Molecular Biologist and has a broad and keen interest in the discovery of nature related things

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