Definition
Enzymes are proteins that catalyze (increase the rates of) chemical reactions.
Basics
Enzymes are special molecules that work as catalysts. This means that enzymes speed up chemical reactions in the body, but do not get used up in the process. Enzymes speed up chemical reactions by lowering the amount of energy needed for a reaction to work. The substances at the start of the reaction are called the substrates. The substances at the end of the reaction are called the products. Enzymes work on the substrates, which later become the products.
Since enzymes are proteins, they are actually large molecules made from many smaller molecules called amino acids. The amino acids hook together like a long chain. If the long chain of amino acids is going to be used to speed up chemical reactions, it is called an enzyme. If the chain of amino acids is going to be used for some other purpose, it is usually called a protein. Different enzymes do different things because their amino acids are hooked together in a different order. Scientists know of many thousands of different enzymes. Sometimes, several small enzymes can hook together like building blocks to make even bigger enzymes.
Enzymes are usually given a name that reflects what they do. Enzyme names usually end in ase to show that they are enzymes. Examples of this include ATP synthase which makes a chemical called ATP. Another example is DNA polymerase, which makes DNA polymers.
One example of an enzyme is amylase. Amylase is found in saliva. Amylase breaks down starch molecules into smaller maltose molecules. These molecules are later broken down into even smaller glucose molecules. Another example is that lypase enzymes break down fats into smaller molecules.
Another example is Protease. Protease is used to break other enzymes and proteins back down into amino acids.
Enzymes are not only for breaking large chemicals into smaller chemicals. Some enzymes take smaller chemicals make build them into bigger chemicals.
Biochemists often want to 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, and the biochemists do not have the time to draw all this detail. This is why biochemists sometimes use ribbon models as pictures of enzymes—they can show the general shape of an enzyme without having to draw each and every atom.
Most enzymes will not work unless the temperature and pH are just right,in most cases the right temperature is 37 degrees (Body Temperature)and the correct pH is 7.
Pepsin is an example of a Enzyme that has a optimum pH of 1.5-2.
Heating an enzyme above a certain temperature will destroy the enzyme permanently, this is called Denaturing an Enzyme. This means that it can no longer be used and it will be broken down by Protease and the chemicals will be reused. Certain chemicals can help an enzyme do its job even better—these are called activators. Other times, 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.
Topics of Interest
Enzymes are proteins that catalyze (i.e., increase the rates of) chemical reactions. In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, called the products. Almost all processes in a biological cell need enzymes to occur at significant rates. Since enzymes are selective for their substrates and speed up only a few reactions from among many possibilities, the set of enzymes made in a cell determines which metabolic pathways occur in that cell.
Like all catalysts, enzymes work by lowering the activation energy (Ea‡) for a reaction, thus dramatically increasing the rate of the reaction. Most enzyme reaction rates are millions of times faster than those of comparable un-catalyzed reactions. As with all catalysts, enzymes are not consumed by the reactions they catalyze, nor do they alter the equilibrium of these reactions. However, enzymes do differ from most other catalysts by being much more specific. Enzymes are known to catalyze about 4,000 biochemical reactions. A few RNA molecules called ribozymes also catalyze reactions, with an important example being some parts of the ribosome. Synthetic molecules called artificial enzymes also display enzyme-like catalysis.
Enzyme activity can be affected by other molecules. Inhibitors are molecules that decrease enzyme activity; activators are molecules that increase activity. Many drugs and poisons are enzyme inhibitors. Activity is also affected by temperature, chemical environment (e.g., pH), and the concentration of substrate. Some enzymes are used commercially, for example, in the synthesis of antibiotics. In addition, some household products use enzymes to speed up biochemical reactions (e.g., enzymes in biological washing powders break down protein or fat stains on clothes; enzymes in meat tenderizers break down proteins, making the meat easier to chew).
History: As early as the late 1700s and early 1800s, the digestion of meat by stomach secretions and the conversion of starch to sugars by plant extracts and saliva were known. However, the mechanism by which this occurred had not been identified.
In the 19th century, when studying the fermentation of sugar to alcohol by yeast, Louis Pasteur came to the conclusion that this fermentation was catalyzed by a vital force contained within the yeast cells called "ferments", which were thought to function only within living organisms. He wrote that "alcoholic fermentation is an act correlated with the life and organization of the yeast cells, not with the death or putrefaction of the cells."
In 1878, German physiologist Wilhelm Kühne, (1837–1900) first used the term enzyme, which comes from Greek ενζυμον, "in leaven", to describe this process. The word enzyme was used later to refer to nonliving substances such as pepsin, and the word ferment was used to refer to chemical activity produced by living organisms.
In 1897, Eduard Buchner began to study the ability of yeast extracts that lacked any living yeast cells to ferment sugar. In a series of experiments at the University of Berlin, he found that the sugar was fermented even when there were no living yeast cells in the mixture. He named the enzyme that brought about the fermentation of sucrose "zymase". In 1907, he received the Nobel Prize in Chemistry "for his biochemical research and his discovery of cell-free fermentation". Following Buchner's example, enzymes are usually named according to the reaction they carry out. Typically, to generate the name of an enzyme, the suffix -ase is added to the name of its substrate (e.g., lactase is the enzyme that cleaves lactose) or the type of reaction (e.g., DNA polymerase forms DNA polymers).
Having shown that enzymes could function outside a living cell, the next step was to determine their biochemical nature. Many early workers noted that enzymatic activity was associated with proteins, but several scientists (such as Nobel laureate Richard Willstätter) argued that proteins were merely carriers for the true enzymes and that proteins per se were incapable of catalysis. However, in 1926, James B. Sumner showed that the enzyme urease was a pure protein and crystallized it; Sumner did likewise for the enzyme catalase in 1937. The conclusion that pure proteins can be enzymes was definitively proved by Northrop and Stanley, who worked on the digestive enzymes pepsin (1930), trypsin and chymotrypsin. These three scientists were awarded the 1946 Nobel Prize in Chemistry.
This discovery that enzymes could be crystallized eventually allowed their structures to be solved by x-ray crystallography. This was first done for lysozyme, an enzyme found in tears, saliva and egg whites that digests the coating of some bacteria; the structure was solved by a group led by David Chilton Phillips and published in 1965. This high-resolution structure of lysozyme marked the beginning of the field of structural biology and the effort to understand how enzymes work at an atomic level of detail.
Enzyme catalysis is the catalysis of chemical reactions by specialized proteins known as enzymes. Catalysis of biochemical reactions in the cell is vital due to the very low reaction rates of the uncatalysed reactions. The mechanism of enzyme catalysis is similar in principle to other types of chemical catalysis. By providing an alternative reaction route and by stabilizing intermediates the enzyme reduces the energy required to reach the highest energy transition state of the reaction. The reduction of activation energy (ΔG) increases the number of reactant molecules with enough energy to reach the activation energy and form the product.
Enzyme inhibitors are molecules that bind to enzymes and decrease their activity. Since blocking an enzyme's activity can kill a pathogen or correct a metabolic imbalance, many drugs are enzyme inhibitors. They are also used as herbicides and pesticides. Not all molecules that bind to enzymes are inhibitors; enzyme activators bind to enzymes and increase their enzymatic activity.
In biochemistry, a substrate is a molecule upon which an enzyme acts. Enzymes catalyze chemical reactions involving the substrate(s). In the case of a single substrate, the substrate binds with the enzyme active site, and an enzyme-substrate complex is formed. The substrate is transformed into one or more products, which are then released from the active site. The active site is now free to accept another substrate molecule. In enzymes with more than one substrate, these may bind in a particular order to the active site, before reacting together to produce products.
An immobilized enzyme is an enzyme which is attached to an inert, insoluble material such as calcium alginate (produced by reacting a mixture of sodium alginate solution and enzyme solution with calcium chloride). This can provide increased resistance to changes in conditions such as pH or temperature. It also allows enzymes to be held in place throughout the reaction, following which they are easily separated from the products and may be used again - a far more efficient process and so is widely used in industry for enzyme catalysed reactions. An alternative to enzyme immobilization is whole cell immobilization.
Enzyme engineering (or enzyme technology) is the application of modifying an enzyme's structure (and thus its function) or modifying the catalytic activity of isolated enzymes to produce new metabolites, to allow new (catalyzed) pathways for reactions to occur, or to convert from some certain compounds into others (biotransformation). These products will be useful as chemicals, pharmaceuticals, fuel, food or agricultural additives. An enzyme reactor consists of a vessel containing a reactional medium that is used to perform a desired conversion by enzymatic means. Enzymes used in this process are free in the solution.
A restriction enzyme (or restriction endonuclease) is an enzyme that cuts double-stranded or single stranded DNA at specific recognition nucleotide sequences known as restriction sites. Such enzymes, found in bacteria and archaea, are thought to have evolved to provide a defense mechanism against invading viruses. Inside a bacterial host, the restriction enzymes selectively cut up foreign DNA in a process called restriction; host DNA is methylated by a modification enzyme (a methylase) to protect it from the restriction enzyme’s activity. Collectively, these two processes form the restriction modification system. To cut the DNA, a restriction enzyme makes two incisions, once through each sugar-phosphate backbone (i.e. each strand) of the DNA double helix.
Enzyme assays are laboratory methods for measuring enzymatic activity. They are vital for the study of enzyme kinetics and enzyme inhibition.
A protease (or proteinase) breaks down proteins. A protease is any enzyme that conducts proteolysis, that is, begins protein catabolism by hydrolysis of the peptide bonds that link amino acids together in the polypeptide chain forming the protein. Proteases work best in acidic conditions.
Enzyme activators are molecules that bind to enzymes and increase their activity. These molecules are often involved in the allosteric regulation of enzymes in the control of metabolism. An example of an enzyme activator working in this way is fructose 2,6-bisphosphate, which activates phosphofructokinase 1 and increases the rate of glycolysis in response to the hormone glucagon.
Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)
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