4.1 The role of enzymes:
• Enzymes are biological catalysts which speed up the rate of reaction by providing an
alternative pathway which lowers the activation energy
• Enzymes are globular proteins.
• They act as catalysts to metabolic reactions in living organisms.
• Enzymes are required to build all the structures of the body (cytoskeleton).
• Enzymes may be intracellular, such as catalase which converts hydrogen peroxide into
oxygen and water
• Enzymes may be extracellular, such as the digestive enzymes amylase and trypsin.
Enzyme properties:
• 3D Shape due to its tertiary structure
• complementary active site to a specific substrate
• high turnover number
• enzyme is left unchanged at the end of the reaction
4.1 Induced fit hypothesis:
• The IF hypothesis helps explain how the activation energy may be reduced.
• The active site of an enzyme molecule does not have a perfectly complementary fit to the
shape of the substrate.
• When the substrate moves into the active site, it interacts and interferes with the bonds
that hold the shape of the active site
• As a result, the shape of the active site is altered to give a perfect fit to the shape of the
substrate.
• This changes the shape of the active site, affecting the bonds in the substrate, making them
easier to make or break.
The course of an enzyme-controlled reaction:
• The substrate is complementary to the active site which means they combine forming an
enzyme substrate complex.
• This destabilises and strains the bonds in the substrate, forming the enzyme product
complex.
4.2 Effect of pH on enzymes:
• All enzymes have an optimum pH, therefore they will not work at a pH outside of this range.
• This is because the hydrogen ions affect the interactions between R groups in the tertiary
structure, so hydrogen or ionic bonds may break
4.2 Effect of temperature on enzymes:
Low temperatures:
• The molecules have little kinetic energy.
• They collide infrequently with the substrate molecules so less ESC are formed, thus activity
decreases.
High temperatures:
• The increased kinetic energy causes the enzyme to vibrate, causing vibration within the
protein molecule
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