IGCSE Biology Paper-1: Specimen Questions with Answers 169 - 169 of 208

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Question 169



Two enzyme-controlled reactions are shown.

Deduction Can be Made About Enzymes

From these reactions, what deduction can be made about enzymes?


Choice (4)


Enzyme 2 slows down the production of amino acids.


Enzymes can build up large molecules.


Enzymes only break down large molecules.


Enzyme 1 has been changed to enzyme 2.




Properties of Enzymes

  • Enzymes are complex macromolecules with high molecular weight.
  • They catalyse biochemical reactions in a cell. They help in the breakdown of large molecules into smaller molecules or bring together two smaller molecules to form a larger molecule.
  • Enzymes do not start a reaction. However, they help in accelerating it.
  • Enzymes affect the rate of biochemical reaction and not the direction of the reaction.
  • Most of the enzymes have a high turnover number. Turnover number of an enzyme is the number of molecules of a substance that is acted upon by an enzyme per minute under saturated substrate concentration. High turnover number of enzymes increases the efficiency of the reaction.
  • Enzymes are specific in action.
  • Enzymatic activity decreases with increase in temperature and all enzymes show maximum activity at an optimum of .
  • They show maximum activity at an optimum pH of 6 – 8.
  • The velocity of enzyme increases with increase in substrate concentration and then, reaches maximum velocity.

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