1.B 7.6Compare competitive inhibition and non-competitive inhibition

2. Inhibitors Chemicals that are able to modify the activity of an enzyme by binding to it. If the inhibitor attaches to the enzyme by covalent bonds, inhibition is irreversible and usually involves the destruction or permanent modification of the enzyme structure. If it attaches by weak interactions, the 3. Competitive inhibitors Chemicals that bind reversibly at the active site of the enzyme and they compete with the substrate for the binding position at the active site. Chemical structure similar to that of the substrate. Block active site and make it unavailable to the substrate. Increasing the substrate concentration decreases the effect of competitive inhibition 4. Effect on the rate of an enzyme-catalyzed reaction Vmax remains the same as there is still a substrate concentration where full activity of the enzyme can be achieved. But as it takes a higher substrate concentration to reach this rate, Km is increased. 5. Example : The conversion that succinic dehydrogenase carries out is: SuccinateFumarate The reaction is inhibited by malonate ions which have a very similar shape to succinate ions. 6. Non-competitive inhibition Chemicals that bind reversibly away from the active site of the enzyme Binding causes conformational change in the protein structure that alters the active site, inhibiting the ability to bind to the substrate. Increasing the substrate concentration has no effect as the enzymes shape still 7. Effect on the rate of an enzyme-catalyzed reaction Vmax is decreased and cannot be restored nomatter how high the substrate concentration. The value of Km is unchanged because theunhibited enzymes are perfectly functional. 8. Examples : Silver ions (heavy metal) react with -SH groups in the side groups of cysteine residues in the protein chain: If the cysteine residue is somewhere on the protein chain which affects the way it folds into its tertiary structure, then altering this group could have an effect on the shape of the active site, and so stop the enzyme from working. 9. B 7.7State and explain the effects of heavy-metal ions, temperature changes and pH changes on enzyme activity 10. Effects of heavy-metal ions Such as lead, copper, mercury and silver arepoisonous, due to their effects on enzymes. When a heavy-metal ion is present at theactive site, substitution of a different metalion for the original ion can cause the enzymeto malfunction and lose its activity. This is particularly evident where heavymetal ions can bind or chelate to the S-H,sulfhydryl groups in proteins to form acovalent bond with the sulfur atom and 11. Effect of temperature Increasing the temperature will initially increase the rate of enzyme-catalyzed reactions, as more reactants will possess the minimum activation energy. The optimum temperature for most enzyme is about 40C. Above this temperature enzymes rapidly become denatured as the weak bonds holding the tertiary structure together break. (Denaturation is the loss of the tertiary structure) Lowering the temperature usually causes deactivation of an enzyme. This prevents the 12. Effect of pH changes At low or high pH values, the enzyme isirreversibly denatured. Each enzyme worksoptimally at a particular pH. At different pH values the charges on the aminoacid residues change affecting the bondsbetween them, and so altering the tertiarystructure and making the enzyme ineffective. It is considered as a way of controlling theiractivity as different enzymes has differentoptimum pH. Eg. pepsin is active in the stomach where pH is