ZymogenIn biochemistry, a zymogen (ˈzaɪmədʒən,_-moʊ-), also called a proenzyme (ˌproʊˈɛnzaɪm), is an inactive precursor of an enzyme. A zymogen requires a biochemical change (such as a hydrolysis reaction revealing the active site, or changing the configuration to reveal the active site) for it to become an active enzyme. The biochemical change usually occurs in Golgi bodies, where a specific part of the precursor enzyme is cleaved in order to activate it.
BacteriaBacteria (bækˈtɪəriə; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among the first life forms to appear on Earth, and are present in most of its habitats. Bacteria inhabit soil, water, acidic hot springs, radioactive waste, and the deep biosphere of Earth's crust. Bacteria play a vital role in many stages of the nutrient cycle by recycling nutrients and the fixation of nitrogen from the atmosphere.
Parietal cellParietal cells (also known as oxyntic cells) are epithelial cells in the stomach that secrete hydrochloric acid (HCl) and intrinsic factor. These cells are located in the gastric glands found in the lining of the fundus and body regions of the stomach. They contain an extensive secretory network of canaliculi from which the HCl is secreted by active transport into the stomach. The enzyme hydrogen potassium ATPase (H+/K+ ATPase) is unique to the parietal cells and transports the H+ against a concentration gradient of about 3 million to 1, which is the steepest ion gradient formed in the human body.
PepsinPepsin 'pɛpsɪn is an endopeptidase that breaks down proteins into smaller peptides. It is produced in the gastric chief cells of the stomach lining and is one of the main digestive enzymes in the digestive systems of humans and many other animals, where it helps digest the proteins in food. Pepsin is an aspartic protease, using a catalytic aspartate in its active site. It is one of three principal endopeptidases (enzymes cutting proteins in the middle) in the human digestive system, the other two being chymotrypsin and trypsin.
FungusA fungus (: fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from the other eukaryotic kingdoms, which, by one traditional classification, includes Plantae, Animalia, Protozoa, and Chromista. A characteristic that places fungi in a different kingdom from plants, bacteria, and some protists is chitin in their cell walls.
DigestionDigestion is the breakdown of large insoluble food molecules into small water-soluble food molecules so that they can be absorbed into the watery blood plasma. In certain organisms, these smaller substances are absorbed through the small intestine into the blood stream. Digestion is a form of catabolism that is often divided into two processes based on how food is broken down: mechanical and chemical digestion. The term mechanical digestion refers to the physical breakdown of large pieces of food into smaller pieces which can subsequently be accessed by digestive enzymes.
GastrinGastrin is a peptide hormone that stimulates secretion of gastric acid (HCl) by the parietal cells of the stomach and aids in gastric motility. It is released by G cells in the pyloric antrum of the stomach, duodenum, and the pancreas. Gastrin binds to cholecystokinin B receptors to stimulate the release of histamines in enterochromaffin-like cells, and it induces the insertion of K+/H+ ATPase pumps into the apical membrane of parietal cells (which in turn increases H+ release into the stomach cavity).
Hydrochloric acidHydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride with the chemical formula HCl(aq). It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the digestive systems of most animal species, including humans. Hydrochloric acid is an important laboratory reagent and industrial chemical.
ProteaseA protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the formation of new protein products. They do this by cleaving the peptide bonds within proteins by hydrolysis, a reaction where water breaks bonds. Proteases are involved in many biological functions, including digestion of ingested proteins, protein catabolism (breakdown of old proteins), and cell signaling.
SecretionSecretion is the movement of material from one point to another, such as a secreted chemical substance from a cell or gland. In contrast, excretion is the removal of certain substances or waste products from a cell or organism. The classical mechanism of cell secretion is via secretory portals at the plasma membrane called porosomes. Porosomes are permanent cup-shaped lipoprotein structures embedded in the cell membrane, where secretory vesicles transiently dock and fuse to release intra-vesicular contents from the cell.
