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Classification and nomenclature of Enzymes
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Classification of substrate

Aprajita Shankhdhar
Loves teaching and tries to simplify teaching learning process as much as possible by my side NEET \ AIIMS \ CTET.

Unacademy user
great explanation sir
  1. Nature of Enzyme Action By : Aprajita Shankhdhar


  2. Each enzyme (E) has a substrate (S) binding site in its molecule so that a highly reactive enzyme-substrate complex (ES) is produced This complex is short-lived and dissociates into its product(s) P and the unchanged enzyme with an intermediate formation of the enzyme-product complex (EP). The formation of the ES complex is essential for catalysis DES ES -EPE P


  3. The catalytic cycle of an enzyme action can be described in the following steps: 1. First, the substrate binds to the active site of the enzyme, fitting into the active site. 2. 2. The binding of the substrate induces the enzyme to alter its shape, fitting more tightly around the substrate. 3. 3. The active site of the enzyme, now in close proximity of the substrate breaks the chemical bonds of the substrate and the new enzyme- product complex is formed. 4. 4. The enzyme releases the products of the reaction and the free enzyme is ready to bind to another molecule of the substrate and run through the catalytic cycle once again


  4. Factors Affecting Enzyme Activity


  5. The activity of an enzyme can be affected by a change in the conditions which can alter the tertiary structure of the protein. These include temperature, pH, change in substrate concentration or binding of specific chemicals that regulate its activity. Temperature and pH Enzymes generally function in a narrow range of temperature and phH Each enzyme shows its highest activity at a particular temperature and pH called the optimum temperature and optimum pH Activity declines both below and above the optimum value. Low temperature preserves the enzyme in a temporarily inactive state whereas high temperature destroys enzymatic activity because proteins are denatured by heat


  6. pH Temperature KIS


  7. Concentration of Substrate With the increase in substrate concentration, the velocity of the enzymatic reaction rises at first. The reaction ultimately reaches a maximum velocity (Vmax) which is not exceeded by any further rise in concentration of the substrate This is because the enzyme molecules are fewer than the substrate molecules and after saturation of these molecules, there are no free enzyme molecules to bind with the additional substrate molecules The activity of an enzyme is also sensitive to the presence of specific chemicals that bind to the enzyme. When the binding of the chemical shuts off enzyme activity, the process is called inhibition and the chemical is called an inhibitor. When the inhibitor closely resembles the substrate in its molecular structure and inhibits the activity of the enzyme, it is known as competitive inhibitor. Due to its close structural similarity with the substrate, the inhibitor competes with the substrate for the substrate binding site of the enzyme. Consequently, the substrate cannot bind and as a result, the enzyme action declines, e.g., inhibition of succinic dehydrogenase by malonate which closely resembles the substrate succinate in structure. Such competitive inhibitors are often used in the


  8. Classification and Nomenclature of Enzymes


  9. Thousands of enzymes have been discovered, isolated and studied Most of these enzymes have been classified into different groups based on the type of reactions they catalyse. Enzymes are divided into 6 classes each with 4-13 subclasses and named accordingly by a four-digit number. Oxidoreductases/dehydrogenases: Enzymes which catalyse oxidoreduction between two substrates S and S' e.g., S reduced S' oxidised-S oxidised S' reduced. Transferases: Enzymes catalysing a transfer of a group, G (other than hydrogen) between a pair of substrate S and S' e.g., S-G+S- S+S'-G


  10. Hydrolases: Enzymes catalysing hydrolysis of ester, ether, peptide, glycosidic, C- C, C-halide or P-N bonds Lyases: Enzymes that catalyse removal of groups from substrates by mechanisms other than hydrolysis leaving double bonds