There are two hypotheses for the formation of an enzyme-substrate complex; the lock and key hypothesis explains that only one substrate (they key) will fit into the active site (lock). The induced fit hypothesis is when the active site changes shape so that the enzyme moulds itself around the substrate. A simple example of the importance of enzymes in digestion is lactose- intolerance. Lactose is a sugar found in milk, and is digested by an enzyme found in the intestines called lactase. A lack of this enzyme can result in lactose- intolerance, whereby the undigested lactose is fermented by bacteria causing a host of intestinal complications.
However, milk can be artificially treated with purified lactase. Even if a person had the best supplemented diet, it would be worthless without the use of enzymes to allow the polymers to be broken down rapidly. The digestive system is just one of the many processes in which enzymes play a key role. The proteins and carbohydrates that we consume are polymers, they are large, insoluble molecules which mean that they cannot be directly absorbed into our blood to be assimilated into new products. They need to be hydrolysed into smaller, more soluble molecules by adding water, this hydrolysis is catalysed by a number of different enzymes.
Two important glands along the digestive system produce and release these enzymes to aid the breakdown of food, firstly, the salivary gland which secretes saliva consisting of the enzyme amylase (a carbohydrase). Secondly, the pancreas releases pancreatic juice consisting of amylase, tripsin, chymotripsin and lipase into the duodenum. As well as the release of enzymes, the pancreas also releases hormones in the regulation of blood glucose.
The alpha cells of the Islets of Langerhans detect a fall in blood glucose and respond by secreting glucagon into the blood, only the receptors on liver cells can respond to the glucagon by activating an enzyme that converts glycogen to glucose, to increase the blood sugar level and return it to a normal level. Without this enzyme, stores of glycogen would not be converted to glucose and the blood sugar level would remain too low.
Genes determine our phenotype because they contain the information to produce an organism’s proteins and enzymes, the order of bases in the gene decide the order of amino acids in the protein and therefore, decide the type of enzyme that is produced. The nature and development of organisms is determined by the metabolic pathways taken by these enzymes.
Mutations in the DNA base sequence may mean that a gene codes for a non-functioning or different enzyme, so the active site is no longer specific to the substrate, and enzyme-substrate complexes cannot be formed therefore, certain metabolic pathways cannot be enabled. Finally, Enzymes are even useful for the manufacture of food for humans, as many are used in the food industry, created from genetically modified bacteria. For example, amylases are produced and used to break down starch during the production of beer and proteases are used to tenderize meat.