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Transcript
Factors Affecting Enzyme Activity Learning Outcomes • apply knowledge of proteins to explain the effects on enzyme activity of: – pH – temperature – substrate concentration – enzyme concentration – competitive inhibitors, and non-competitive inhibitors including heavy metals • differentiate between the roles of enzymes and coenzymes in biochemical reactions • identify the role of vitamins as coenzymes Factors affecting enzyme activity • • • • • Temperature pH Concentration Activation Inhibitors • Co-enzymes • What happens to the rate of most chemical reactions as the temperature is increased? • Why? Temperature • All enzymes have an optimal temperature • Up to this temperature, the reaction rate increases as temperature increases • Above this temperature, denaturation of the enzyme occurs (irreversible) • What would you expect to be the optimal temperature of enzymes that function in the human body? Effect of temperature on enzyme activity Enzyme activity Optimal temperature Temperature • How might a strong acid or base affect a protein? pH • All enzymes have an optimal pH • High or low pH causes reduced enzyme activity and denaturation of the enzyme Effect of pH on enzyme activity Enzyme activity Optimal pH pH Fig. 6.8 • What happens if we increase or decrease the concentration of substrate? Substrate concentration • Increasing the substrate concentration increases the reaction rate • only to the point where all enzymes are being used Effect of substrate concentration Enzyme activity Substrate concentration • What if we add more enzyme? • How would this happen in the body? Enzyme concentration • In cells, enzyme concentration is genetically controlled (control of protein synthesis) • Increasing the amount of enzyme will increase the reaction rate (as long as substrate is present) Effect of enzyme concentration Enzyme activity Enzyme concentration Activation • Enzymes may be “turned on” by the presence of another molecule (ex. The addition of a phosphate group, known as phosphorylation) Enzyme activation • How could you prevent a substrate from binding to an enzyme active site? • Would this ever be a desirable outcome? Inhibition • Inhibitors are molecules other than the substrate that bind to the enzyme and inhibit its activity Competitive inhibition • Competitive inhibitors compete with the substrate by binding to the active site Non-competitive inhibition • Non-competitive inhibitors bind to a different site on the enzyme (allosteric site) • Change the shape of the enzyme’s active site • Toxic heavy metals such as lead, cadmium and mercury can bind to enzymes causing denaturation • Act as non-competitive inhibitors Feedback inhibition • Sometimes the product of the pathway acts as an inhibitor • This stops the pathway when there is enough of the product Fig. 6.9a Fig. 6.9b Enzyme cofactors • Cofactors or coenzymes are non-protein molecules that assist the enzyme • May be inorganic ions ex. Copper, zinc, or iron • Often are organic molecules derived from vitamins • Function is often to transfer electrons or functional groups (ex. Phosphate) to the substrate • Vitamin deficiency results in interference with enzyme activity in various metabolic pathways (so eat your veggies!)
