Mode of action of enzymes
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Define intracellular and extracellular enzymes, and give an example of each.
Intracellular enzymes catalyse reactions inside cells (
Explain how enzymes speed up biochemical reactions.
Enzymes lower the activation energy of a reaction. By forming an enzyme-substrate complex, the reaction pathway is altered, reducing the energy required for the reaction to proceed, thus increasing the reaction rate.
Describe the 'lock-and-key' hypothesis of enzyme action.
The lock-and-key hypothesis proposes that the active site of an enzyme has a rigid shape complementary to a specific substrate. The substrate fits perfectly into the active site like a key in a lock, forming the enzyme-substrate complex.
Describe the 'induced-fit' hypothesis of enzyme action.
The induced-fit hypothesis proposes that the active site of the enzyme is not a rigid shape, but rather changes shape to fit the substrate. This conformational change stresses the substrate's bonds, facilitating the reaction.
What is an enzyme-substrate complex?
An enzyme-substrate complex is the intermediate structure formed when a substrate molecule binds to the active site of an enzyme. This interaction facilitates the chemical reaction by bringing reactants together and/or straining chemical bonds.
Outline the steps involved in investigating the rate of amylase activity.
Mix amylase with a starch solution. At regular intervals, remove samples and add them to iodine solution. Measure the time taken for the iodine solution to stop turning blue-black, indicating starch has been broken down. Control variables like temperature and pH.
How can a colorimeter be used to measure the progress of an enzyme-catalysed reaction that involves a colour change?
A colorimeter measures the absorbance or transmission of light through a solution. As a coloured product is formed (or a coloured reactant is used up), the absorbance will change. This change can be used to quantify the rate of the reaction.
Explain what is meant by 'enzyme specificity'.
Enzyme specificity refers to the ability of an enzyme to catalyse a reaction with only one particular substrate or a small number of structurally similar substrates. This is due to the unique shape of the enzyme's active site which is complementary to the shape of the specific substrate.
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