Temperature And Concentration On Enzyme Catalyse Reactions Biology Essay


Chemistry is the science concerned with the composition, behavior, structure, and properties of matter, as well as the changes it undergoes during chemical reactions. Biochemistry is the study of the chemicals, chemical reactions and chemical interactions that take place in living organisms. Hydrogen peroxide is generated during the reduction of molecular oxygen in cells. Hydrogen peroxide is extremely toxic to living cells. It can damage DNA, protein and lipid membranes, and may even be a causative factor in cancer. Catalase is an enzyme found in plant and animal cells that aids in the disproportionation of hydrogen peroxide. (Bodnik. 2004) (Wikipedia, Hydrogen Peroxide, Jan. 2010.)

Enzymes are the proteins that catalyze chemical reactions in our body. They speed up reactions by providing an alternative reaction pathway of lower activation energy. (Chem.Purdue.Edu.) They also allow chemical reactions to occur fast enough to support life. And they are complex molecules that enable thousands of essential chemical reactions in the body. We need enzymes to properly digest and assimilate the food we eat. The two classes of enzymes are, metabolic and digestive. Metabolic enzymes speed up the chemical reaction within the cells for detoxification and energy production. They enable us to see, hear, feel, move and think. Every organ, every tissue, and all 100 trillion cells in our body depend upon the reaction of metabolic enzymes and their energy factor. Metabolic enzymes are produced by every living cell. However, the liver, pancreas, gallbladder and other organs play a vital role in their production. Enzymes are only present in small amounts in the cell since they are not altered during their reactions. A substrate is a molecule upon which an enzyme acts. In the case of a single substrate, the substrate binds with the enzyme active site, and an enzyme-substrate complex is formed. The active site is the part of an enzyme where the chemical reaction occurs. This active site contains the catalytic and binding sites. (Enzymedica.com. 2008)

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In the case of catalase, the enzyme provides a site containing iron, which changes valence states readily, stripping the oxygen off of the hydrogen peroxide. While the complete mechanism of catalase is not currently known, the reaction is believed to occur in two stages:

H2O2 + Fe(III)-E â†' H2O + O=Fe(IV)-E(.+)

H2O2 + O=Fe(IV)-E(.+) â†' H2O + Fe(III)-E + O2

Here Fe()-E represents the iron centre of the heme group attached to the enzyme. Fe(IV)-E(.+) is a mesmeric form of Fe(V)-E, meaning that iron is not completely oxidized to +V but receives some "supporting electron" from the heme ligand. This heme has to be drawn then as radical cation (.+).

As hydrogen peroxide enters the active site, it interacts with the amino acids (ligands), around the active site, causing a proton (hydrogen ion) to transfer between the oxygen atoms. The free oxygen atom coordinates with the help of ligands, freeing the newly-formed water molecule and an iron (IV) complex. The iron complex reacts with a second hydrogen peroxide molecule to reform the catalase enzyme and produce water and oxygen. The reactivity of the iron center is be improved by the presence of ligands, which assist in orientating the hydrogen peroxide and asisting the oxidation of the iron molecule. In general, the rate of the reaction can be determined by the Michaelis-Menten equation (Wikipedia, Catalase, 22 Jan. 2010). (Stevens. 1962.)

The common factors that affect the rate of a chemical reaction are temperature, pressure, concentration, and catalyst. One of the factors that affect the rate of a chemical reaction is temperature. Higher temperature increases the rate of the reaction by increasing the amount of energy available. Another one is concentration. Increasing the concentration of the reactants can increase the rate of reaction. The forth one is use of a catalyst. Catalyst speeds up the rate of reaction by reducing the energy needed for a reaction to occur. Once the energy needed has been reduced, the reaction can proceed more quickly. Irons, like all the transition metals, have multiple stable valence states that help it form transition products. That is why transition metals, iron in particular, are very important in a catalyst chemical reaction. ( Helmenstine.)

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Oxidation is the addition of oxygen to a compound with a loss of electrons. Reduction is the gain of electrons or a decrease in oxidation state by a molecule, atom or ion. Redox (shorthand for reduction-oxidation reaction) describes all chemical reactions in which atoms have their oxidation number changed. An antioxidant is a molecule capable of slowing or preventing the oxidation of other molecules. Antioxidants are substances that block or inhibit destructive oxidation reactions and inhibit enzymes that cause inflammatory responses. The hydrogen peroxide starts to proportionate and becomes oxidized. This special form of redox/oxidation is known as disproportion.

Enzyme kinetics is the study of the chemical reactions that are catalyzed by enzymes. In enzyme kinetics the reaction rate is measured and the effects of varying the conditions of the reaction investigated. Studying an enzyme's kinetics in this way can reveal the catalytic mechanism of this enzyme, its role in metabolism, how its activity is controlled, and how a drug or a poison might inhibit the enzyme. An important goal of measuring enzyme kinetics is to determine the chemical mechanism of an enzyme reaction. Rates of reaction are usually measured by using the purified enzyme in vitro with the substrate and then observing the formation of the product or disappearance of the substrate. Enzymes (which are large protein molecules) are nature's catalysts. The vast majority of chemical reactions that keep living things alive are much too slow (without a catalyst) to sustain life. (Chem.edu. June 2004) (Wikipedia.org, Jan 2010.)

A few of the things that effects the rate of catalase are; temperature, enzyme concentration, hydrogen peroxide concentration and inhibitor concentration. According to the laws of thermodynamics, all chemical reactions are affected by temperature. Temperature increases the rate of reaction of catalase, although excessive temperature can cause enzymes to breakdown. The effect of enzyme concentration on the rate of reaction is very profound and in most cases is kept low. The Michaelis-Menten equation predicts that the reaction rate will increase rapidly with increased hydrogen peroxide concentration until maximum rate is reached. The rate of reaction will decrease with increasing inhibitor concentration. The disproportionation of hydrogen peroxide by the enzyme catalase is 2x1011 faster than the non-catalylized reduction.