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Enzymes Summary Notes

What are enzymes?

Enzymes are protein molecules that act as biological catalysts.

  • They alter the rate of chemical reactions in living organisms
  • They are not used up in the reaction.
  • Enzymes are capable of either joining smaller molecules to form larger molecules or split larger molecules into smaller molecules.
  • Enzymes control a specific chemical reaction.
  • They work by lowering the activation energy needed to start a chemical reaction.

How enzymes are named

Types of enzymes are generally named after their substrate or the type of reaction they catalyse, for example:

  • protease acts on proteins
  • lipase acts on lipids
  • sucrase acts on sucrose
  • maltase acts on maltose

Characteristics of enzymes

  • Enzymes are specific in their actions — one type of enzyme acts on one specific substrate molecule or catalyse a specific reaction.
  • Enzymes are not altered or used up at the end of the reaction.
  • Enzymes speed up a chemical reaction even at low enzyme concentration.
  • Enzyme catalysed reaction are reversible where the forward and reversed reactions are catalysed by the same enzyme. However reactions usually proceed from left to right because the products are not allowed to build up.
  • Enzyme catalysed reactions can be stopped or slowed down by inhibitors such as mercury, lead and arsenide

Rate of enzyme catalysed reaction is affected by:

  • Temperature
  • pH
  • Substrate concentration
  • Enzyme concentration

Effects of temperature on enzyme activity

  • An increase in temperature increase the rate of enzyme activity because heat increases the kinetic energy of the enzyme and substrate molecules. This increases the rate of molecular collisions between the enzyme and its substrate leading to a faster reaction.
  • Most enzymes function at an optimum temperature of 40°C.
  • Above 40°C enzyme activity decreases.
  • At about 60°C enzyme activity ceases because the enzymes become denatured and coagulated.
  • Low temperatures decreases enzyme activity.

Effects of pH on enzyme activity

  • Different enzymes have different optimum pH working conditions, however, extreme changes in pH causes enzymes to be denatured.
  • When enzymes are denatured, they become inactivated.

Uses of enzymes

  • Amylase catalyses the hydrolysis of starch to maltose.
  • Maltase catalyses the hydrolysis of maltose to glucose.
  • Protease catalyses the hydrolysis of protein to amino acids.
  • Lipase catalyses the hydrolysis of fats to form glycerol and fatty acids.

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