Difference Between Biosynthetic and Degradative Pathways

The key difference between biosynthetic and degradative pathways is that biosynthetic pathway synthesizes complex molecules from simpler molecules while degradative pathway breaks down complex and larger molecules into simpler molecules. 

A metabolic pathway is a series of enzyme-catalyzed biochemical reactions which occurs within a cell. There are two types of metabolic pathways: biosynthetic or anabolic pathway and degradative or catabolic pathway. These two metabolic pathways work together as the energy released from one pathway is used by the other pathway. Metabolic pathways are necessary to maintain homeostasis within an organism. They also maintain and regulate the flux of metabolites depending on the availability of substrates. The final products of these metabolic pathways are either used up immediately, initiate another pathway or stored to be used when needed. Each of these metabolic pathways consists of chemical reactions that are interconnected by their intermediate products. Metabolic pathways are usually unidirectional but, the chemical reactions are reversible.

CONTENTS

1. Overview and Key Difference
2. What are Biosynthetic Pathways
3. What are Degradative Pathways
4. Similarities – Biosynthetic and Degradative Pathways
5. Biosynthetic vs Degradative Pathways in Tabular Form
6. Summary

What are Biosynthetic Pathways?

A biosynthetic pathway is a series of chemical and metabolic reactions catalyzed by enzymes in the synthesis of a specific end product in a living organism. In this pathway, simple compounds are modified and converted to various other compounds or form macromolecules. Biosynthetic pathway is also known as anabolic pathway since it involves the formation of macromolecules. Elements necessary for the biosynthesis process includes precursor compounds, chemical energy molecules such as ATP and catalytic enzymes along with co-enzymes such as NADH. These elements create monomers that form macromolecules.

Biosynthetic pathways consist of a series of chemical reactions. For those reactions to take place, several elements are necessary. They are precursor compounds, chemical energy, catalytic enzymes and co-enzymes or cofactors. Precursor compounds are known as the substrate or the starting molecule in a reaction. In other words, they are called reactants. Catalytic enzymes are special proteins that increase the rate of reaction by lowering the activation energy. Co-enzymes or cofactors assist a chemical reaction. Metal ions and vitamin derivatives such as NADH or acetyl co-A and other molecules such as ATP act as co-enzymes or cofactors. Finally, the chemical energy is found as high energy molecules such as ATP. The chemical energy is necessary to construct macromolecules such as polypeptides, proteins, polysaccharides, nucleic acids, and lipids. Therefore, the biosynthetic pathway is an endergonic pathway as energy is absorbed or used up. In a living organism, hormones involved in the biosynthetic pathway are estrogen, testosterone, insulin and growth hormone.

What are Degradative Pathways?

A degradative pathway is a series of enzyme-catalyzed biochemical reactions that results in the breakdown of large molecules or polymers. Degradative pathway is also known as catabolic pathway since it involves the breakdown of larger molecules into smaller units. In a degradative pathway, the energy released in the form of high energy phosphate bonds with energy carriers such as ADP and GDP to produce ATP and GTP, respectively. This results in lower free energy in the final products. Therefore, the degradative pathway is an exergonic pathway as free energy is released. It produces chemical energy in the form of ATP, GTP, NADPH, NADH and FADH₂ from complex sources like carbohydrates, lipids and proteins. The final products of such chemical reactions are usually carbon dioxide, water and ammonia.

In a degradative pathway, the monomers that are released from the breakdown of polymers are used to degrade simple waste products further by releasing energy. These cellular wastes are lactic acid, carbon dioxide, acetic acid, ammonia and urea. This process is usually an oxidation process. Degradative pathway, therefore, provides chemical energy for the maintenance and growth of cells. In a living organism, hormones that involve in the degradative pathway are Adrenaline, cortisol, glucagon and cytokines.

Similarities Between Biosynthetic and Degradative Pathways

1. These pathways are metabolic pathways.
2. Both pathways involve energy.
3. They consist of chemical reactions catalyzed by enzymes.

Difference Between Biosynthetic and Degradative Pathways

The biosynthetic pathway involves anabolism where simpler molecules or substrates transform into larger complex molecules such as polysaccharides, proteins, lipids and nucleic acids. The degradative pathway involves catabolism where larger complex molecules break down to simpler molecules such as monosaccharides, amino acids, fatty acids and nucleotides. So, this is the key difference between biosynthetic and degradative pathways. Moreover, biosynthetic pathways use up energy while degradative pathways release energy.

The following infographic lists the differences between biosynthetic and degradative pathways in tabular form for side by side comparison.

Summary – Biosynthetic vs Degradative Pathways

Biosynthetic pathway and degradative pathway are involved in metabolism. These metabolic pathways are a series of enzyme-catalyzed biochemical reactions occurring within a cell. Biosynthetic pathway is a series of biochemical reactions involved in the synthesis of complex molecules from smaller and simple molecules using up chemical energy. Degradative pathway is a series of biochemical reactions involved in the breakdown of complex molecules into simpler molecules releasing chemical energy. Metabolic pathways are usually unidirectional but, the chemical reactions are reversible. Thus, this summarizes the difference between biosynthetic and degradative pathways.

Reference:

1. “Biosynthetic pathway.” Science Direct.
2. “Catabolism vs. Anabolism: Hormones, body weight, and exercises.” Healthline.

Image Courtesy:

1. “CoA Biosynthetic Pathway” By Kristenfdz – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “2519 Energy From Amino Acids” By OpenStax College – Anatomy: Physiology, Connexions Web site, Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia