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Biology AS CIE

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  1. 1-cell-structure
    10 主题
  2. 2-biological-molecules
    19 主题
  3. 3-enzymes
    13 主题
  4. 4-cell-membranes-and-transport
    16 主题
  5. 5-the-mitotic-cell-cycle
    8 主题
  6. 6-nucleic-acids-and-protein-synthesis
    9 主题
  7. 7-transport-in-plants
    11 主题
  8. 8-transport-in-mammals
    16 主题
  9. 9-gas-exchange
    6 主题
  10. 10-infectious-diseases
    6 主题
  11. 11-immunity
    10 主题
课 3, 主题 13
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3-1-mode-of-action-of-enzymes AS enzymes

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Exam code:9700

Enzymes as proteins

  • Enzymes are biological catalysts

    • ‘Biological’ because they function in living systems

    • ‘Catalysts’ because they speed up the rate of chemical reactions without being used up or changed

  • Enzymes are also globular proteins

  • Critical to the enzyme’s function is the active site where the substrate binds

  • Metabolic pathways are controlled by enzymes in a biochemical cascade of reactions

    • Virtually every metabolic reaction within living organisms is catalysed by an enzyme – enzymes are therefore essential for life to exist

  • Enzymes can be intracellular or extracellular referring to whether they are active inside or outside the cell respectively

    • Intracellular enzymes are produced and function inside the cell

    • Extracellular enzymes are secreted by cells and catalyse reactions outside cells (e.g. digestive enzymes in the gut)

 

Intracellular

Extracellular

Example

Catalase

Amylase

Function

Hydrogen peroxide is produced as a by-product of many cellular reactions

It is harmful to cells

Catalase converts hydrogen peroxide into water and oxygen, preventing cell damage

Digestion of food is carried out by extracellular enzymes

This is because macromolecules of food are too large to enter cells

Amylase is an an example of a digestive enzyme

It digests carbohydrates into simple sugars

Examiner Tips and Tricks

Don’t forget that enzymes are proteins and so anything that could denature a protein, rendering it non-operational (extremes of heat, temperature, pH etc.) would also denature an enzyme.

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