![]() ![]() ![]() According to lock and key model, enzymes behave as rigid molecules.Once the product is formed, they no longer fit into the active site and escape into surrounding medium.The remaining amino acids which make the bulk of the enzyme, function to maintain the correct globular shape of the enzyme. Most enzymes are far larger than the substrates molecules that act on and the active site is usually a very small portion of the enzyme, between 3 and 12 amino acids.Enzymes catalyze only those substrates which fit perfectly on the active site of that enzyme.the substrate is like a key whose shape is complementary to the enzyme which is supposed to be lock and they fit perfectly. According to this model, shape of active site of enzyme is complementary to the shape of substrate molecules.Turn over number is defined as number of substrate molecule converted into product by one enzyme molecule in one second. Efficiency of enzyme is expressed in turn over number.Rate of enzyme catalyzed reaction is usually (10^3- 10^8) times faster than uncatalysed reaction.Enzyme catalyzed reaction are highly efficient.similarly, enzyme hexokinase phosphorylates many hexose sugar including, glucose, galactose, mannose etc. For example, enzyme Alcohol dehydrogenase bring dehydrogenation of many alcohols such as methanol, ethanol etc. This type of specificity is known as group specificity. ii) Group specificity: some enzymes acts on group of closely related substrates.For example, catalase enzyme acts on H2O2 only. i) Absolute specificity: if enzyme acts on only one type of substrate, it is called absolute specificity.One is absolute specificity and other is group specificity. There are two types of enzyme specificity.A particular enzyme catalyze particular type of biochemical reaction. Enzyme catalyzed reaction are highly specific ie.
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