Metabolism is the set of life-sustaining chemical transformation within the cells of living organism.
The word metabolism can also refer to all chemical reactions that occur in living organisms, including digestion and the transport of substances into and between different cells, in which case the set of reactions within the cells is called intermediary metabolism or intermediate metabolism.
Metabolism is further divided into two categories anabolism and catabolism.
Catabolism breaks-down organic material and harvest energy by cellular respiration and anabolism that uses energy to construct component of cell such as nucleic acid and proteins.
Amino acids and proteins:
Proteins are made of amino acid arranged in a linear chain joined together by peptide bond. Many proteins are enzymes that catalyze the chemical reactions in metabolism.
Proteins are also important in cell signaling, immune responses, cell adhesion, active transport across membranes, and the cell cycle. Amino acids also contribute to cellular energy metabolism by providing a carbon source for entry into the citric acid cycle.
Carbohydrates are macro-molecules defined as polyhydroxy aldehydes or ketones. The basic carbohydrate units are called monosaccharides and include galactose, fructose and most importantly glucose.
|chemical digestion in humans.|
Macromolecules such as starch, cellulose or proteins cannot be rapidly taken up by cells and must be broken into their smaller units before they can be used in cell metabolism. Several common classes of enzymes digest these polymers.These digestive enzymes include proteases that digest proteins into amino acids that digest polysaccharides into simple sugars known as monosaccharides. Microbes simply secrete digestive enzymes into their surroundings,while animals only secrete these enzymes from specialized cells in their guts.The amino acids or sugars released by these extracellular enzymes are then pumped into cells by active transport proteins.