Catabolic pathway or breakdown pathway is a fundamental metabolic process in living organisms that involves the breakdown of complex molecules into simpler ones, often resulting in the release of energy. It is a crucial part of cellular metabolism and plays a central role in providing the necessary energy for various biological processes.
During catabolic reactions, large molecules such as carbohydrates, lipids, and proteins are enzymatically degraded into smaller units. For example, complex carbohydrates like starch or glycogen are broken down into glucose molecules, proteins are broken down into amino acids, and triglycerides (a type of lipid) are broken down into glycerols and fatty acids.
The primary purpose of catabolic pathway is to extract energy stored within these complex molecules. The energy released during catabolic processes is typically in the form of chemical bonds, which are broken and converted into a more usable form such as adenosine triphosphate (ATP). ATP is the primary energy currency of the cell and is used to power various cellular functions.
Catabolism is not only responsible for energy production but also for the recycling and elimination of waste products. For instance, Some decaying organelles, cells and misassembled proteins are broken down into amino acids, saccharides and lipids by hydrolytic enzymes within the lysosome, and these nutrients are reused by the cell.
Anabolic pathway or biosynthetic pathway encompasses several important processes, including fat synthesis, glycogen synthesis, and protein synthesis. These pathways involve the construction of complex molecules from simpler building blocks and play crucial roles in energy storage, cellular function, and growth.
Glycogen synthesis, also called glycogenesis, is the process by which glucose molecules are combined and stored as glycogen in liver and muscle cells. It occurs when an excess of glucose is ingested. Glycogen serves as a readily available energy source that can be rapidly broken down when energy demands increase. This process is regulated by hormones such as insulin, which stimulates the uptake of glucose into cells and promotes glycogen synthesis.
Fat synthesis, also known as lipogenesis, is an anabolic process in which fatty acids and glycerol are combined to form triglycerides, the primary storage form of fats in the body. This process occurs primarily in adipose tissue (fat cells) and the liver, when glycogen are exceeded.
The building blocks for fat synthesis are obtained from excess dietary carbohydrates. Some are converted to glycerol. Others become acetyl CoA in the citric acid cycle, which is used to synthesize fatty acids. Through a series of enzymatic reactions, glycerol and fatty acids are joined together to form the triglycerides. These triglycerides are then stored in adipose tissue as an energy reserve to be utilized when needed.
Protein synthesis, also known as translation, is occurs in the ribosomes, with the help of messenger RNA (mRNA) molecules that carry the genetic information from DNA.
Two amino acids undergo a dehydration reaction to generate a peptide bond (-CO-NH-) in the ribosome. These amino acids are added to the peptide chain one by one through the dehydration reaction. The peptide chain is also modified by folding and glycosylation. Protein synthesis requires a lot of energy and the peptide chain stays in the endoplasmic reticulum for half an hour or longer.