Enzymes: Globular proteins which act as catalysts of chemical reactions.
Active site: Region on the surface of an enzyme to which substrates bind and which catalyses a chemical reaction involving the substrates.
The active site of an enzyme is very specific to its substrates as it has a very precise shape. This results in enzymes being able to catalyze only certain reactions as only a small number of substrates fit in the active site. This is called enzyme-substrate specificity. For a substrate to bind to the active site of an enzyme it must fit in the active site and be chemically attracted to it. This makes the enzyme very specific to it’s substrate. The enzyme-substrate complex can be compared to a lock and key, where the enzyme is the lock and the substrate is the key.
Enzyme activity increases with an increase in temperature and usually doubles with every 10 degrees rise. This is due to the molecules moving faster and colliding more often together. However at a certain point the temperature gets to high and the enzymes denature and stop functioning. This is due to the heat causing vibrations within the enzyme destroying its structure by breaking the bonds in the enzyme.
Enzymes usually have an optimum pH at which they work most efficiently. As the pH diverges from the optimum, enzyme activity decreases. Both acid and alkali environments can denature enzymes.
Enzyme activity increases with an increase in substrate concentration as there are more random collisions between the substrate and the active site. However, at some point, all the active sites are taken up and so increasing the substrate concentration will have no more effect on enzyme activity. As long as there are active sites available, an increase in substrate concentration will lead to an increase in enzyme activity.
Denaturation is changing the structure of an enzyme (or other protein) so it can no longer carry out its function.
Lactose is the sugar found in milk. It can be broken down by the enzyme lactase into glucose and galactose. However some people lack this enzyme and so cannot break down lactose leading to lactose intolerance. Lactose intolerant people need to drink milk that has been lactose reduced. Lactose-free milk can be made in two ways. The first involves adding the enzyme lactase to the milk so that the milk contains the enzyme. The second way involves immobilizing the enzyme on a surface or in beads of a porous material. The milk is then allowed to flow past the beads or surface with the immobilized lactase. This method avoids having lactase in the milk.
TOPIC 2.5: Enzymes
Essential Idea: Enzymes control the metabolism of the cell.
At SHS, Topic 2.5 is taught in the following class unit(s):
Statements & Objectives:
2.5.U1 Enzymes have an active site to which specific substrates bind.
2.5.U2 Enzyme catalysis involves molecular motion and the collision of substrates with the active site.
2.5.U3 Temperature, pH and substrate concentration affect the rate of activity of enzymes.
2.5.U4 Enzymes are denatured.
2.5.U5 Immobilized enzymes are widely used in industry.
2.5.A1 Methods of production of lactose-free milk and its advantages.
2.5.S1 Design of experiments to test the effect of temperature, pH, and substrate concentration on the activity of enzymes.
2.5.S2 Experimental investigation of a factor affecting enzyme activity.(Practical 3)
2.5.NOS Experimental design-accurate, quantitative measurements in enzyme experiments require replicates to ensure reliability.