Enzymes


Enzymes are biological catalysts; they speed up metabolic reactions by lowering energy barriers without being consumed by the reaction. Proteins in quaternary structure form enzymes. The chemical structure of an enzyme is related to its specificity and catalytic activity. Induced fit, cofactors, inhibitors, and specific active sites all affect the specificity and catalytic activity of enzymes. Being a protein, enzymes are affected by changes in conditions of their environment. In an experiment testing the affect of high temperature on a pure catalyst, results of changes in conditions for enzymes is further explained.


Enzymes are catalytic proteins. A protein is one or more polypeptides folded and coiled into specific conformations. A polypeptide is a polymer of amino acids connected in a specific sequence. The sequence of amino acids determine what three dimensional conformation a protein will take which determines how the protein will work. There are four levels of protein structure: Primary, secondary, tertiary, and quaternary. Primary structure is a single polypeptide chain where amino acids are held together by peptide bonds. Primary structure of a protein is determined by inherited genetic information. When hydrogen bonds occur at regular intervals along the polypeptide backbone the result is secondary structure. Segments of a proteins polypeptide chain is repeatedly coiled or folded in patterns that contribute to a proteins overall conformation. One type of secondary structure, alpha helix, is a delicate coil held together by hydrogen bonds between every forth-amino acid. Beta pleated sheets, another type of secondary structure is when two or more regions of a polypeptide chain lie parallel to each other and are held together by hydrogen bonds between parts of the backbone in the parallel regions. Superimposed on the patterns of secondary structure is a proteins tertiary structure, consisting of irregular contortions form interactions between side chains of various amino acids. In a hydrophobic interaction, as a polypeptide folds into its functional conformation, amino acids with hydrophobic side chains usually end up in clusters at the core of the protein and are held together by van der waals interactions. Tertiary structure is further stabilized by ionic and hydrogen bonds between side chains and by disulfide bridges between two cytosine monomers. The overall protein structure is quaternary structure, which is when two or more polypeptide chains are aggregated into one functional macromolecule that interacts in cellular metabolism.


Metabolic reactions are speeded up by catalytic proteins-enzymes that lower the activation energy barrier. Activation energy is provided in the form of heat which when absorbed breaks bonds in the reactant molecules. Since high heat denatures proteins enzymes are used to lower the activation barrier so the transition state (unstable molecules that are activated and ready for making and breaking of bonds) can be reached under moderate temperatures.


Enzymes are very selective in the reactions they catalyze. An enzyme binds to a specific substrate or reactant and converts it to a product. An enzymes specific conformation creates an active site, a “groove” or “pocket” where the enzyme binds to a specific substrate. As the substrate enters the active site it slightly changes fitting more snugly called induced fit, which brings chemical groups of the active site into positions that enhance their ability to catalyze the chemical reaction. The substrate is held in the active site by weak interactions while side chains of a few amino acids catalyze the conversion of substrate to product, which then departs from the active site. Sometimes Cofactors, no protein helpers for catalytic activity, are needed which bind tightly with the active site or loosely with the substrate.


Certain chemicals selectively inhibit the action of specific enzymes by weak bonds or strong covalent bonds. Competitive inhibitors compete for admission to the active site reducing the productivity of enzymes by blocking substrates from entering active sites. Noncompetitive inhibitors bind to a part of the enzyme other that the active site changing the enzymes shape causing the active site to become unreceptive or less effective. Inhibitors are used as a type of metabolic control.


A cells chemical and physical environment also affects enzyme activity. A change of conditions in a proteins environment such as pH or temperature can cause proteins to denature or lose their native conformation. The denaturization of enzymes causes lower enzymatic activity.


In an experiment testing the effects of high