Metabolism is the process of extracting nutrients from organic compounds for cell utilization in growth, repair, maintenance, and reproduction. There are two types of reactions: catabolic and anabolic. Catabolic reactions break down organic compounds into smaller molecules to release ATP in respiration– an example is digestion. In anabolic reactions, smaller molecules are combined to form larger organic compounds using ATP – examples are carbon fixation, bone growth and nucleotide synthesis. Anabolism is fueled by catabolism, where catabolic reactions releases ATP for which anabolic reactions utilize to build organic compounds.
Reactions in metabolism are mediated by enzymes, globular proteins that catalyzed biochemical reactions by lowering activation energy. Enzymes take part in metabolic pathways, where they convert larger molecules into a smaller form that can be used by the cell. They are important in metabolism because they couple breaking down compounds with respiration, speed up biochemical reactions and have a regulatory function. Key chemicals that are involved in metabolism are: carbohydrates, lipids, proteins and nucleotides.
Regulation of catabolism and anabolism occur in homeostasis where hormones and neurotransmitters send signals. The signals can increase or decrease enzyme activity, and athe rate of the whole metabolic pathway. There are two types of control: intrinsic and extrinsic. Intrinsic control is when self-regulation is applied when the concentration of products or reactants passes threshold, whilst extrinsic control is when the whole metabolic pathway is altered. An example of a regulatory hormone is cortisol.