Chemical Reactions Occur When Atoms, Molecules, and

Chemical reactions occur when atoms, molecules, and ions interact with one other to form new substances. Chemical bonds are broken and new bonds are formed. Chemical bonds between atoms follow rules based on patterns of electron distribution within the involved atoms. When reactions take place, energy exchange occurs. When chemical bonds are broken, energy is released. When new bonds are formed, energy is stored. There are many types of chemical reactions. They can be loosely classified by the type of chemical change taking place.

Several basic reaction types are encountered in cellular processes. Hydrolytic reactions use the addition of water molecules to break apart large molecules. Hydrolysis is used during digestion to break large molecules down into their smaller components. In a hydrolytic reaction, the hydroxyl group from the water molecule is added to one part of the larger molecule and the hydrogen atom is added to the other side of the molecule. If water is added, without splitting the molecule in two, the reaction is called a hydration reaction.

Dehydration synthesis or condensation reactions are the reverse of hydrolysis. Water is removed from the reactants to produce a new larger molecule when the two reactants minus water bond. Dehydration synthesis plays an important role in the construction of organic polymers. Dehydration synthesis is used to assemble monosaccharides to make complex sugars, and is used to join amino acids to make proteins, or to join nucleotides to make a nucleic acid. Other important reactions are phosphorylation and dephosphorylation, which involves the addition and removal of a phosphate group.

This reaction pair is important because the phosphate group is strongly electronegative and bonds formed with the phosphate group have the potential to be high energy bonds. Dephosphorylation is the reverse of phosphorylation, removing one of the phosphate groups. An isomerization reaction occurs when the atoms of a molecule are rearranged, but there is no addition or removal of atoms. For example, glucose and fructose are isomers of each other; both molecules have the same molecular formula, but differ in the arrangement of the atoms.

Oxidation and reduction reactions involve the addition or removal of oxygen or hydrogens. These are among the more complex, but also most important reactions in living systems. Oxidation reactions involve either the addition of oxygen or the removal of hydrogen, hydrogen ions, or electrons. Reduction reactions involve the removal of oxygen or the addition of hydrogens, hydrogen ions, or electrons. Often oxidation and reduction go hand in hand,.