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biology finals for a high school student!!?
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Enzymes are biomolecules that catalyze (i.e., increase the rates of) chemical reactions.[1][2] Nearly all known enzymes are proteins. However, certain RNA molecules can be effective biocatalysts too. These RNA molecules have come to be known as ribozymes.[3] 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 or ΔG‡) 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.[4] A few RNA molecules called ribozymes catalyze reactions, with an important example being some parts of the ribosome.[5][6] Synthetic molecules called artificial enzymes also display enzyme-like catalysis.[7]
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).
Etymology and history
Eduard BuchnerAs early as the late 1700s and early 1800s, the digestion of meat by stomach secretions[8] 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.[9]
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."[10]
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.[11] He named the enzyme that brought about the fermentation of sucrose "zymase".[12] 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 e
Like all catalysts, enzymes work by lowering the activation energy (Ea or ΔG‡) 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.[4] A few RNA molecules called ribozymes catalyze reactions, with an important example being some parts of the ribosome.[5][6] Synthetic molecules called artificial enzymes also display enzyme-like catalysis.[7]
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).
Etymology and history
Eduard BuchnerAs early as the late 1700s and early 1800s, the digestion of meat by stomach secretions[8] 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.[9]
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."[10]
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.[11] He named the enzyme that brought about the fermentation of sucrose "zymase".[12] 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 e
An enzymatic reaction is a chemical reaction involving enzymes. Enzymes are complex proteins that act as biological catalysts, helping to speed biochemical reactions in living things. Because they are catalysts, enzymes are not used up in these reactions; they only increase the rate at which they occur. For example, the enzyme amylase is present in saliva and breaks down starch in food into sugar. The substances that enzymes act upon are called substrates (in the above example, starch is the substrate). One final thing: enzymes are very specific as to the reactions they facilitate—enzyme molecules form complementary shapes to their intended substrates, almost like a lock and key combination.
An enzymatic reaction is a chemical reaction involving enzymes. Enzymes are complex proteins that act as biological catalysts, helping to speed biochemical reactions in living things. Because they are catalysts, enzymes are not used up in these reactions; they only increase the rate at which they occur. For example, the enzyme amylase is present in saliva and breaks down starch in food into sugar. The substances that enzymes act upon are called substrates (in the above example, starch is the substrate). One final thing: enzymes are very specific as to the reactions they facilitate—enzyme molecules form complementary shapes to their intended substrates, almost like a lock and key combination.