Metabolism

1. The major part of the chemical alterations occurring in a biological system are at cellular level. At this level, growth, maintenance of health, or disease are affected by the entry of chemical substances and their influence on the cell. Excluding the extracellular process of digestion (in the case of higher organisms) the chemical transformation of nutrients which constitutes metabolism takes place in the cell.

2. Metabolism essentially is the development of the more complex molecules which the organism needs from simpler ones. A critical factor in successful metabolism is the action of nutrient-freeing protein enzymes present in the cell. Nutrient-freeing is among nearly 100 types of enzyme-induced metabolic changes. These include the synthesis and breakdown by the enzyme of its own fats, carbohydrates, proteins, nucleic acids and lipids. The mechanics of metabolic cell control are central to the investigations of DNA and other cellular materials in bio-genetic engineering.