Enzyme – simple english wikipedia, the free encyclopedia c gastronomie limonest


Enzymes are large molecules made from many amino acids. The amino acids link together in a long chain, which is folded up into a complex structure. Enzymes have a part which holds the substrate: a "claw, cleft, hollow or knob to grasp, hold, stretch and bend the molecule it acts on, the substrate". [2] p37

There are thousands of different enzymes. Enzymes have names which show what they do. Enzyme names usually end in –ase to show that they are enzymes. Examples of this include ATP synthase. It makes a chemical called ATP. Another example is DNA polymerase. It reads an intact DNA strand and uses it as a template to make a new strand.

Biochemists often draw a picture of an enzyme to use as a visual aid or map of the enzyme. This is hard to do because there may be hundreds or thousands of atoms in an enzyme. Biochemists can not draw all this detail. Instead, they use ribbon models as pictures of enzymes. Ribbon models can show the shape of an enzyme without having to draw every atom.

Most enzymes will not work unless the temperature and pH are just right. In mammals the right temperature is usually about 37 oC degrees (body temperature). The correct pH can vary greatly. Pepsin is an example of an enzyme that works best when pH is about 1.5. [4]

Some chemicals can help an enzyme do its job even better. These are called activators. Sometimes, a chemical can slow down an enzyme or even make the enzyme not work at all. These are called inhibitors. Most drugs are chemicals that either speed up or slow down some enzyme in the human body. Lock and key model [ change | change source ]

Enzymes are very specific. In 1894 Emil Fischer suggested that both the enzyme and the substrate have specific complementary geometric shapes that fit exactly into one another. [5] This is often referred to as "the lock and key" model. However, this model fails to explain what happens next.

• Enzyme production ( transcription and translation of enzyme genes) can be increased or reduced in response to changes in the cell’s environment. This form of gene regulation is called enzyme induction and inhibition. For example, in bacteria which are resistant to antibiotics such as penicillin, enzymes are induced which hydrolyse the penicillin molecule.

• Enzymes can occur in different cellular compartments. For example, fatty acids are synthesized by one set of enzymes in the cytosol, endoplasmic reticulum and Golgi apparatus. Then they are used by a different set of enzymes as a source of energy in the mitochondria. [8]

• Enzymes can be regulated by their own products. For example, the end product(s) often inhibit one of the first enzymes of the pathway. Such a regulatory mechanism is called negative feedback, because the amount of the end product produced is regulated by its own concentration. This prevents the cells making too much enzyme. The control of enzyme action helps keep a stable internal environment in living organisms.

• Enzymes can be regulated by being modified after their production. An example is the cleavage of the polypeptide chain. Chymotrypsin, a digestive protease, is produced in inactive form in the pancreas and transported in this form to the stomach where it is activated. This stops the enzyme from digesting the pancreas or other tissues before it enters the gut. This type of inactive precursor to an enzyme is known as a zymogen.

• Some enzymes may become activated when they move to a different environment (e.g. from high pH to low pH). For example, haemagglutinin in the influenza virus is activated by a change in shape. This is caused by the acidic conditions which occur inside the host cell’s lysosome. [9]

Cofactors, or coenzymes, are helper molecules which are needed to make an enzyme work. They are not proteins, and may be organic or inorganic molecules. Both types of molecules sometimes contain a metal ion at the centre, such as Mg 2+, Cu 2+, Mn 2+ or iron- sulphur clusters. This is because such ions may act as electron donors, and this is important in many reactions. The need of enzymes for various little helpers is the basic reason why animals, including ourselves, need trace elements and vitamins. [10] [11] Classification [ change | change source ]