Enzymes – The nature catalysts

Nature is the most productive of chemical industries. It turns out billions of tonnes of a vast range of products every year using the simplest of starting materials. The catalysts that make all this possible are enzymes – the biological catalysts. As with inorganic catalysts, enzymes speed up chemical reaction without themselves being used up in the course of the reaction. Enzymes are able to catalyse reactions in aqueous solutions under exceptionally mild conditions of temperature and pH.

Enzymes are very specific, generally catalysing only one particular reaction. Carbonic anhydrase, for instance, is an enzyme in red blood cells that catalyses the reaction:

CO₂ + H₂O → H₂CO₃

This enzyme increases the rate of this reaction up to a million fold, increasing the efficiency of removal of carbon dioxide from our bloodstream. In a cellular environment this specificity is absolutely essential – an enzyme must be able to distinguish one amino acid from another or one nucleotide from another. Thus although enzymes are functioning within the rules that define catalytic activity, they differ from ordinary chemical catalysts in several important respects. The rates of enzyme catalysed reactions are typically increased by factors up to 10¹² times compared to the incatalysed reaction. There are several orders of magnitude greater than those of the corresponding chemically catalysed reaction. Enzyme catalysed reactions occur under relatively mild conditions: temperature below 100˚C, atmospheric pressure, and at pH’s around 7. Enzymes have a vastly more defined specificity with regard to their substrate and products. Enzyme catalysed reactions do not produce side products. The catalytic activities of many enzymes can be varied by the concentrations of substances other than the substrate. The mechanism of these regulatory processes can be complex.

Majority of enzymes are water soluble globular proteins. The complicated folding of the protein chain to form the tertiary structures gives rise to clefts of precise geometric shape on the surface of the enzyme. Locks and keys are complementary structures and this would also explain enzyme specificity. One substrate will fit into the active site, just as only one key fits a lock.

Enzymes, as other catalyst function by providing an alternative reaction pathway that requires lower activation energy (Ea). Thus, more molecular interactions posses sufficient energy to produce products. The overall reaction between enzyme and its substrate can be represented by the following equation:

ENZYME (LOCK) + SUBSTRATE (KEY) ↔ ENZYME – SUBSTRATE (KEY IN LOCK) → ENZYME + PRODUCTS

The first stage of the reaction is reversible since if that available energy is not greater than Ea the complex may dissociate without product being formed. In some cases the second stage is also reversible, making the whole enzyme catalysed process capable of proceeding in either direction depending on the cells metabolic requirements. Once the products have been formed, they leave the active site of the enzyme. The enzyme is then free to combine with a new substrate molecule. Enzymes like inorganic catalysts, are not used up in the reaction they catalyst so they can be used again and again.

The youtube video about enzyme in our daily life.

For more informations, visit http//www.rsc.org/education/teachers/learnnet/cfb/enzymes.htm