• Genes work collectively producing enzymes in a squence. - Results in a metabolic pathway

• Metabolic pathways are extremely efficient but can be disrupted by mutations in the genes which are involved.

• Gene mutations may result in enzymes with altered structures

E.g. Deletion, Substitution, or Insertion mutations may cause this

• By influencing the substrates available, the activity of enzymes and the pathways taken the cell metabolism can be extremely responsive.

• Catabolic – reactions that release energy while breaking large molecules into smaller molecules

e.g. the breakdown of glucose in respiration

• The breakdown of complex molecules into simple molecules, releasing energy in the form of ATP

• Anabolic – reactions that require energy while building larger molecules from smaller molecules

e.g. the building of proteins from amino acids

• The build up of complex molecules from simple molecules. Energy from ATP is required to power the reaction

- Alternative pathways allow for steps in the pathway to be bypassed.