In a living cell, many different things happen at the same time in a well-planned and integrated way. Metabolism (anabolism and catabolism) is the group name for all of the chemical reactions that take place in a living system.
A metabolic pathway (or metabolic map) is a set of enzymatic reactions that result in the production of particular metabolites. In metabolic reactions, the term metabolite refers to a substrate, an intermediary, or a product. Metabolic processes are roughly split into two classes.
Catabolic reaction: The breakdown of complex molecules into simpler ones, accompanied by the release of energy.
Anabolism process: The biosynthetic reactions that result in the creation of complex compounds from simple ingredients.
Since both catabolism and anabolism share a number of intermediates, drawing a firm line between the two is challenging. Amphibolism is also used to describe processes that can be either catabolic or anabolic.
What Is Catabolism?
What is catabolism? The objective of catabolic reaction is to capture the energy of biomolecules as ATP and produce the chemicals (precursors) necessary for the synthesis of complex molecules. There are three phases of catabolism reaction.
Figure 1: The three stages of catabolic reaction.
Conversion of complex molecules: Conversion of complex molecules into their constituents. Polysaccharides are broken down into monosaccharides, lipids are broken down into free fatty acids and glycerol, and proteins are broken down into amino acids.
Formation of simple intermediates: The building blocks produced in stage (1) are degraded to simple intermediates such as pyruvate and acetyl CoA. These intermediates are not readily identifiable as carbohydrates, lipids or proteins. A small quantity of energy (as ATP) is captured in stage 2.
Final oxidation of acetyl CoA of ATP: Acetyl CoA is completely oxidized to CO2, liberating NADH and FADH2 that finally get oxidized to release large quantity of energy (as ATP). Krebs cycle (or citric acid cycle) is the common metabolic pathway involved in the final oxidation of all energy-rich molecules. This pathway accepts the carbon compounds (pyruvate, succinate etc.) derived from carbohydrates, lipids or proteins.
What Is Anabolism?
What is anabolism? For the synthesis of a large variety of complex molecules, the starting materials are relatively few. These include pyruvate, acetyl CoA and the intermediates of citric acid cycle. Besides the availability of precursors, the anabolism process are dependent on the supply of energy (as ATP or GTP) and reducing equivalents (as NADPH+ H+).
The anabolism process and catabolic reaction are not reversible and operate independently. As such, the metabolic pathways occur in specific cellular locations (mitochondria, microsomes etc.) and are controlled by different regulatory signals.
The terms intermediary metabolism and energy metabolism are also in use. Intermediary metabolism refers to the entire range of catabolic and anabolism process, not involving nucleic acids. Energy metabolism deals with the metabolic pathways concerned with the storage and liberation of energy.
FAQs on Anabolism and Catabolism
Cellular respiration is a catabolic process that breaks down glucose to release usable energy (ATP) for the cell.
Photosynthesis is an anabolic process in which plants use sunlight energy to convert carbon dioxide gas and water molecules into sugar molecules.
Gluconeogenesis is an example of an anabolic process. In this anabolism process, a metabolic pathway builds a molecule (glucose) from smaller molecules.
Anabolism is the creation of complex substances from simpler ones.
Ribosomes are the places where protein anabolism process occurs within a cell.