Enzymology: Study of enzymes is called enzymology.

Enzyme: Enzymes are defined as: "Thermolabile biological catalysts which speed up a chemical reaction by lowering the activation energy without undergoing any change."

Catalyst: Catalyst is a substance which speeds up the chemical reaction in non living things without undergoing any change. So enzymes are biological catalysts because they catalyze reactions in living things.

Substrate: The substance on which enzyme act is called substrate.

Discovery of enzymes: The word enzyme means " in yeast" because they were 1st discovered in an extract of yeast.

Activation enzyme: The amount of energy required to activate the reactants so that they can react to form product is called activation enery
or energy required to make substances react is called activation energy.
Reactants must collide with a certain amount of energy in order to react, this critical level is called energy of activation. Normally the activation energy of reactants is high so the reactions are slow. Enzymes speeds up the chemical reaction by lowering the activation energy.

Characteristics of enzymes:
1. Enzymes are protein in nature.
2. All enzymes three dimensional globular proteins.
3. They are formed inside a living cell.
4. Being proteins they are coded by DNA.
5. Enzymes are biological catalysts.
6. They are required in small quantity. An enzyme molecule can break down 100000 molecules/sec of other compounds.
7. Enzymes are highly specific.
8. Enzymes always catalyze a single reaction.
Ex. Amylase only breaks the starch amylose.
9. The functional specificity of every enzyme is the consequence of its specific chemistry and configuration.
10. The reactions catalyzed by enzymes are reversible.




The enzymes are larger than substrates but small part of enzyme called active site comes in contact with substrate where reaction takes place. Enzymes can work inside as well as outside the tissues.Enzymes can be studied both in vivo ( Living cell) and in vitro (Glass wares.Enzymes can be isolated and crystallized.. In crystal form enzymes are pure. Enzymes work with the help of co-enzymes.Enzymes are named by adding "ase" to the name of substrate.Ex: The enzyme that breaks cellulose is called cellulase. Enzymes can be used again and again because there is no change in enzyme before and after the chemical reaction.Enzymes require aqous medium for their activity.Most enzymes remain attached to organneles.Regards

Mode of Action of Enzymes: An Enzyme combines with it's substrate to

form a short lived unstable enzyme substrate complex. Once a reaction has

occured the complex breaks up into products and enzyme. The enzyme

remains unchanged at the end of the reaction.

Enzyme + Substrate======Enzyme substrate complex====Ezyme+product.

To explain the mechanism of action of enzymes there are two hypothesis.

1) LOCK AND KEY HYPOTHESIS: It was proposed by Emil Fischer. According

to this model substrate is like a key and enzyme is like a lock which has

complementary structure to that of substrate. Enzyme is a globular protein

with one or more surface depression or clefts called active sites. These

active sites have particular shapes into which specific substrates fits

exactly.

Once a product is formed in active site it leaves the active site and escapes

into the surrounding medium. As a result active site is free to bind another

substrate.

According to this the active site is a rigid structure. There is no modification

or flexibility in the active site during or after the enzyme action and it is used

only as template. But later studies did not support this model.

Regards..

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