2.4 CHEMICAL REACTIONS AND ENZYMES
A chemical reaction is a process that changes, or transforms, one set of chemical into another. Some reaction occur slowly (such as rust), while other occurs much faster. The elements or compounds that enter a chemical reaction are known as reactants. The elements or compounds produced by a chemical are known as products . Chemical reactions always involve changes in the chemical bonds that join atoms in compound.
The reaction show below enables the bloodstream to carry carbon dioxide to the lungs. In the lungs, the reaction is reversed. CO2+H2O=H2CO3. the reverse reaction produce carbon dioxide gas when you exhale. H2CO3=CO2+H2O.
Chemical reactions that release often occur spontaneously. Chemical reactions that absorb energy will not occur without a source of energy. The energy is released in the form of heat, and sometimes when hydrogen gas explodes, light and sound is released. Every organism must have a source of energy to carry out chemical reactions. Plants get their energy from sunlight. Animals get their energy from other animals or plants.
Chemical reactions release energy does not always occur spontaneously. Chemists call the energy that is needed to get a reaction started the activation energy. Some chemical reactions that make life possible are too slow or have activation energies that are too high to make practical for living tissue. A catalyst is a substance that speeds up the rate of a chemical reaction. Enzymes are protein that act as biological catalysts. Enzymes speed up chemical reactions that takes place in cells. Like other catalysts, enzymes act by lowering the activation energies. Without enzymes, the reaction is too slow.
The reactants of enzyme catalyzed reactions are known as substrates. The substrates bind to a site called the active site. The fits is so precise that the active site and the substrates are often compared to a lock and key. They remain bound together until the reaction is done. Once the reaction is over, the products of the reaction are released and the enzyme is free to start the process again. Most cells contain proteins that help to turn key enzymes "on" or "off" at critical stages in the life of the cell.
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