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Table of Contents
5.1 Enzyme Action
5.1 Enzyme Action
1. Describe a catalyst as a substance that increases the rate chemical reaction and is not changed by the reaction
2. Describe enzymes as proteins that function as biological catalysts and are involved in all metabolic reactions
3. Explain enzyme action concerning the substrate, active site, enzyme-substrate complex, and product
3. Explain enzyme action concerning the substrate, active site, enzyme-substrate complex, and product
Enzymes are specific to one particular substrate (molecules that get broken down or joined together in the reaction), as the enzyme is a complementary shape to the substrate
The product is made from the substrate and is released
An enzyme-controlled reaction involves a substrate, an enzyme and a product. The substrate and product may be two or more different molecules:
The substance on which an enzyme works is called its substrate. The molecules produced are called the products. For example, the enzyme sucrase works on the substrate sucrose to produce the monosaccharide products glucose and fructose.
4. Explain the specificity of enzymes in terms of the complementary shape and fit of the active site with the substrate(‘lock and key’ hypothesis)
4. Explain the specificity of enzymes in terms of the complementary shape and fit of the active site with the substrate(‘lock and key’ hypothesis)
Enzymes are specific to one particular substrate as the active site of the enzyme, where the substrate attaches, is a complementary shape to the substrate.
This is because the enzyme is a protein and has a specific 3-D shape. This is known as the lock and key hypothesis
When the substrate moves into the enzyme’s active site, it becomes known as the enzyme-substrate complex
After the reaction has occurred, the products leave the enzyme’s active site as they no longer fit, and it is free to take up another substrate.
How enzymes work
How enzymes work
1. Enzymes and substrates randomly move about in solution
2. When an enzyme and its complementary substrate randomly collide, with the substrate fitting into the active site of the enzyme, an enzyme-substrate complex forms, and the reaction occurs.
3. A product forms from the substrate, which is then released from the active site. The enzyme is unchanged and will go on to catalyse further reactions.
5.2 Effects of temperature and pH
5.2 Effects of temperature and pH
1. Understand that the progress of enzyme-catalysed reactions can be followed by measuring the concentrations of reactants and products
2. Investigate and describe the effects of temperature and pH on enzyme activity
3. Explain the effect of changes in temperature and pH on enzyme activity in terms of kinetic energy, shape and fit, denaturation and the frequency of effective collisions.
3. Explain the effect of changes in temperature and pH on enzyme activity in terms of kinetic energy, shape and fit, denaturation and the frequency of effective collisions.
Temperature
Temperature
Enzymes are proteins and have a specific shape, held in place by bonds.
This is extremely important around the active site area as the specific shape is what ensures the substrate will fit into the active site and enable the reaction to proceed.
Enzymes work fastest at their ‘optimum temperature’ – in the human body, the optimum temperatureis37⁰C
Heating to high temperatures(beyond the optimum) will break the bonds that hold the enzyme together and it will lose its shape -this is known as denaturation.
Substrates cannot fit into denatured enzymes as the shape of their active site has been lost.
Denaturation is irreversible – once enzymes are denatured, they cannot regain their proper shape and activity will stop.
Increasing the temperature from 0⁰C to the optimum increases the activity of enzymes as the more energy the molecules have, the faster they move, and the number of collisions with the substrate molecules increases, leading to a faster rate of reaction.
This means that low temperatures do not denature enzymes; they just make them work more slowly
pH
pH
The optimum pH for most enzymes is 7, but some are produced in acidic conditions, such as the stomach, have a lower optimum pH (pH 2)and some are produced in alkaline conditions, such as the duodenum, have a higher optimum pH (pH 8 or 9).
If the pH is too high or too low, the bonds that hold the amino acid chain together to make up the protein can be destroyed.
This will change the shape of the active site, so the substrate can no longer fit into it, reducing the rate of activity
Moving too far away from the optimum pH will cause the enzyme to denature, and activity will stop
Credits: Notes compiled by Manahil Naeem of Karachi Grammar School
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