Difference Between Anabolism and Catabolism

Main Difference – Anabolism vs Catabolism

Anabolism and catabolism are the sets of metabolic processes, which are collectively identified as metabolism. Anabolism is the set of reactions involved in the synthesis of complex molecules, starting from the small molecules inside the body. Catabolism is the set of reactions involved in the breakdown of complex molecules like proteins, glycogen, and triglycerides into simple molecules or the monomers like amino acids, glucose, and fatty acids respectively. The main difference between anabolism and catabolism is that anabolism is a constructive process and the catabolism is a destructive process.

This article explains,

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

What is Anabolism

The set of reactions which synthesizes complex molecules, starting from small molecules is known as anabolism. Thus, anabolism is a constructive process. Anabolic reactions require energy in the form of ATP. They are considered as endergonic processes. The synthesis of complex molecules builds up tissues and organs by a step-by-step process. These complex molecules are required for the growth, development, and differentiation of cells. They increase the muscle mass and mineralizes the bones. Many hormones like insulin, growth hormone and steroids are involved in the process of anabolism.

Three stages are involved in anabolism. During the first stage, precursors like monosaccharides, nucleotides, amino acids and isoprenoids are produced. Secondly, these precursors are activated using ATP into an active form. Thirdly, these reactive forms are assembled into complex molecules like polysaccharides, nucleic acids, polypeptides, and lipids.

Organisms can be divided into two groups depending on their ability to synthesize complex molecules from simple precursors. Some organisms like plants can synthesize complex molecules in the cell, starting from a single carbon precursor like carbon dioxide. They are known as autotrophs. Heterotrophs utilize intermediately complex molecules like monosaccharides and amino acids to synthesize polysaccharides and polypeptides, respectively. On the other hand, depending on the energy source, organisms can be divided into two groups as phototrophs and chemotrophs. Phototrophs obtain energy from the sunlight while chemotrophs obtain energy from the oxidation of inorganic compounds. 

Carbon fixation from carbon dioxide is achieved either by photosynthesis or chemosynthesis. In plants, photosynthesis occurs through light reaction and Calvin cycle. During photosynthesis, glycerate 3-phosphate is produced, hydrolyzing ATP. Glycerate 3-phosphate is later converted into glucose by gluconeogenesis. The enzyme glycosyltransferase polymerizes the monosaccharides in order to produce monosaccharides and glycans. An overview of photosynthesis is shown in figure 1.

Figure 1: Photosynthesis

During fatty acid synthesis, acetyl-CoA is polymerized to form fatty acids. Isoprenoids and terpenes are large lipids synthesized by the polymerization of isoprene units during mevalonate pathway. During amino acid synthesis, some organisms are capable of synthesizing essential amino acids. Amino acids are polymerized into polypeptides during protein biosynthesis. De novo and salvage pathways are involved in synthesizing of nucleotides, which can be then polymerized to form polynucleotides during DNA synthesis.

What is Catabolism

The set of reactions which breaks down complex molecules into small units is known as catabolism. Thus, catabolism is a destructive process. Catabolic reactions release energy in the form of ATP as well as heat. They are considered as exergonic processes. The small units of molecules produced in the catabolism can be either used as precursors in other anabolic reactions or to release energy by oxidation. Thus, catabolic reactions are considered to produce chemical energy required by the anabolic reactions. Some cellular wastes like urea, ammonia, lactic acid, acetic acid and carbon dioxide are also produced during catabolism. Many hormones like glucagon, adrenaline, and cortisol are involved in catabolism.

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

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 during digestion by digestive enzymes. Monosaccharides are then used in the glycolysis to produce acetyl-CoA. This acetyl-CoA is used in the citric acid cycle. ATP is produced by the oxidative phosphorylation. 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. The process of cellular respiration, containing glycolysis, citric acid cycle, and oxidative phosphorylation is shown in figure 2.

Figure 2: Cellular Respiration

Difference Between Anabolism and Catabolism

Definition

Anabolism: Anabolism is the metabolic process where simple substances are synthesized into complex molecules.

Catabolism: Catabolism is the metabolic process which breaks down large molecules into smaller molecules.

Role in Metabolism

Anabolism: Anabolism is the constructive phase of metabolism.

Catabolism: Catabolism is the destructive phase of metabolism.

Energy Requirement

Anabolism: Anabolism requires ATP energy.

Catabolism: Catabolism releases ATP energy.

Heat

Anabolism: Anabolism is an endergonic reaction.

Catabolism: Catabolism is an exergonic reaction.

Hormones

Anabolism: Estrogen, testosterone, growth hormone, insulin, etc. are involved in anabolism.

Catabolism: Adrenaline, cortisol, glucagon, cytokines, etc. are involved in catabolism.

Oxygen Utilization

Anabolism: Anabolism is anaerobic; it does not utilize oxygen.

Catabolism: Catabolism is aerobic; it utilizes oxygen. 

Effect on the Body

Anabolism: Anabolism increases the muscle mass. It forms, repairs and furnishes the tissues.

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

Functionality

Anabolism: Anabolism is functional at resting or sleeping.

Catabolism: Catabolism is functional at body activities.

Energy Conversion

Anabolism: Kinetic energy is converted into potential energy during anabolism.

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

Processes

Anabolism: Anabolism occurs during photosynthesis in plants, protein synthesis, glycogen synthesis and assimilation in animals.

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

Examples

Anabolism: The synthesis of polypeptides from amino acids, glycogen from glucose and triglycerides from fatty acids are examples for the anabolic processes.

Catabolism: The breakdown of proteins into amino acids, glycogen into glucose and triglycerides into fatty acids are examples for catabolic processes.

Conclusion

Anabolism and catabolism can be collectively called as the metabolism. Anabolism is a constructive process which utilizes energy in the form of ATP. It occurs during processes such as photosynthesis, protein synthesis, glycogen synthesis. Anabolism stores the potential energy in the body, increasing the body mass. Catabolism is a destructive process which releases the ATP which can be used during the anabolism. It burns the stored complex molecules, reducing the body mass. The main difference between anabolism and catabolism is the type of reactions involved in the two processes. 

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

Image Courtesy:
1. “Simple photosynthesis overview” By Daniel Mayer (mav) – original imageVector version by Yerpo – Own work (GFDL) via Commons Wikimedia
2. “2503 Cellular Respiration” By OpenStax College – Anatomy & Physiology, Connexions Web site. Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia