Denaturation refers to the loss of a protein or nucleic acid’s three-dimensional shape, without changing its chemical composition. This can be caused by heat, chemicals, or organic solvents, and can lead to a loss of protein function. Denatured alcohol is an example of a substance made inedible for tax purposes.
Denaturation means making a substance ineffective for some purpose without changing its chemical composition. The term has a number of more specific meanings, but is most commonly used in connection with proteins and nucleic acids. These are made up of chain-like molecules that can fold up in a variety of ways to form complex three-dimensional shapes. The links in the chains are held together by strong covalent bonds, but the folds arise from a variety of bond types that are usually weaker and can be broken by heat and various chemicals. Molecules are said to have been denatured when some or all of these bonds have been broken, causing them to lose their shape, but leaving the chains intact and the chemical composition unchanged.
Structure of proteins and nucleic acids
Proteins are made up of amino acids and are organized on different structural levels. The primary structure is simply the sequence of building blocks of amino acids that define the protein. These building blocks are held together by covalent bonds known as peptide bonds. Secondary, tertiary, and quaternary structures describe the three-dimensional arrangements of protein subunits, whole proteins, and protein complexes. These structures arise from chains of amino acid blocks that fold back on themselves, due to the formation of various types of relatively weak bonds between units in different parts of the chain.
The secondary structure arises from the hydrogen bonding between a hydrogen atom in one amino acid unit and an oxygen atom in another. This can produce a spiral or sheet-like formation, or a combination of both. The tertiary structure results from the bonds that form between these coils and sheets, giving a three-dimensional protein unit. The quaternary structure is formed by the union of two or more of these units.
Tertiary and quaternary structures are held together by a variety of bond types, including hydrogen bonds. Covalent disulfide bonds can also form between sulfur atoms in two amino acid units. “Salt bridges” form when parts of oppositely charged molecules attract each other in a similar way to the ionic bonds found in salts.
Denaturation generally does not affect the primary structure, but causes degradation of the complex three-dimensional arrangements of proteins. Most protein function arises from chemical traits resulting from the three-dimensional arrangements of amino acid chains, so degradation of those structures generally results in a loss of protein function. Enzymes are an important class of proteins where the shapes of the molecules are crucial to their functions.
Nucleic acids, like DNA and RNA, have two strands made up of units known as bases. The strands are bound together in a double helix shape by hydrogen bonds between the bases on opposite sides. During denaturation, the strands are separated by the breaking of these bonds.
Causes of denaturation
A number of factors can cause the denaturation of proteins and nucleic acids. Heating causes the molecules to vibrate more vigorously, which can lead to the breaking of bonds, especially the weaker ones. Many proteins will be denatured when heated above 105.8°F (41°C), due to the breaking of hydrogen bonds. A familiar example is the change that occurs in egg white when it is heated: the protein albumin is denatured and changes from a clear gel to a white solid. Proteins are also denatured when food is cooked, a process that kills harmful microorganisms.
Denaturation can also be caused by various chemicals. Strong acids and bases, due to their ionic nature, interact with salt bridges which help hold the tertiary structures of proteins together. The positively and negatively charged parts of these compounds are attracted to the oppositely charged parts of a protein salt bridge, breaking the bond between different parts of the protein chain. Salts of some metals can also have this effect.
Covalent disulfide bonds can also be broken, leading to denaturation. Compounds of some heavy metals, such as lead, mercury and cadmium, can do this, because they bind easily with sulfur. The sulfur-sulfur bond can also be broken when each sulfur atom bonds with a hydrogen atom. Some reducing agents will produce this effect.
Various organic solvents can also have a denaturing effect by breaking the hydrogen bonds between amino acids which maintain the tertiary structure. An example is ethanol, commonly called alcohol. It forms its own hydrogen bonds with parts of protein molecules, replacing the original ones.
Denatured alcohol
The term “denaturation” is sometimes used to refer to the process of making a food or drink inedible, but still useful for some function other than consumption. The most common example is denatured alcohol, also known as denatured alcohol. The product is often used as a solvent or fuel, and taxes levied on drinking alcohol can be avoided when used for other purposes if it is rendered undrinkable. The alcohol itself is not chemically altered, but additives, usually methanol, make it toxic.
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