The rate of reaction when the enzyme is saturated with substrate is the maximum rate of reaction, Vmax. The relationship between rate of reaction and concentration of substrate depends on the affinity of the enzyme for its substrate. This is usually expressed as the Km Michaelis constant of the enzyme, an inverse measure of affinity. For practical purposes, Km is the concentration of substrate which permits the enzyme to achieve half Vmax. An enzyme with a high Km has a low affinity for its substrate, and requires a greater concentration of substrate to achieve Vmax.
The Km of an enzyme, relative to the concentration of its substrate under normal conditions permits prediction of whether or not the rate of formation of product will be affected by the availability of substrate. An enzyme with a low Km relative to the physiological concentration of substrate, as shown above, is normally saturated with substrate, and will act at a more or less constant rate, regardless of variations in the concentration of substrate within the physiological range.
An enzyme with a high Km relative to the physiological concentration of substrate, as shown above, is not normally saturated with substrate, and its activity will vary as the concentration of substrate varies, so that the rate of formation of product will depend on the availability of substrate. A good example is a lightning strike that starts a forest fire which, once started, will continue to burn until the fuel is used up.
In biology, chemical reactions are often aided by enzymes , biological molecules made of proteins which can be thought of as facilitators or catalysts. Enzymes speed the reaction, or allow it to occur at lower energy levels and, once the reaction is complete, they are again available.
In other words, they are not used up by the reaction and can be re-used. Enzymes are designed to work most effectively at a specific temperature and pH. Outside of this zone, they are less effective. At very high temperatures, enzymes, because they are made of protein, can be denatured or destroyed. The material on which the enzyme will act is called the substrate.
The enzyme attaches to the substrate molecule at a specific location called the active site. When the enzyme has attached to the substrate, the molecule is called the enzyme-substrate complex.
For example, the sugar found in milk is called lactose. With the aid of the enzyme, lactase , the substrate, lactose, is broken down into two products, glucose and galactose. Enzyme action can be blocked by molecules that obstruct the enzyme's active site. Herbicides and pesticides often work in this way. The active site of an enzyme has a very specific 3-dimensional shape.
Therefore, enzymes are specific to particular substrates, and will not work on others with different configurations. The enzyme can then bind another substrate. A typical enzyme kinetics curve for a non-allosteric enzyme is shown in the graph: An explanation for the shape of the enzyme kinetics curve At low substrate concentration the reaction rate increases sharply with increasing substrate concentration because there abundant free enzyme available E to bind added substrate.
Activation Energy of the Iodine Clock Reaction. Different Types of Enzymes. Role of Enzymes in Chemical Reactions.
What Is Runaway Polymerization?
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