factors affecting enzyme activity. learning outcomes apply knowledge of proteins to explain the...

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

Temperature

Enzyme activity

Optimal 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

pH

Optimal 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!)