Enzymes
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(Credits to Mustafa Asif)
Notes
Enzymes:
Biological catalysts made of protein. They alter the rate of chemical reactions without themselves being chemically changed at the end of the reaction.
Catalysts are substances that can change the speed of a chemical reaction.
Characteristics of enzymes
They alter or speed up the rates of chemical reactions that occur in a cell.
They remain unchanged after a chemical reaction.
They are specific.→"Lock & Key" hypothesis (One enzyme act on one substrate)
They are affected by temperature.
They are affected by pH.
They may need other enzymes to work (Coenzymes).
They catalyse reversible reactions.
Factors affecting enzyme activity
temperature
The enzyme activity is increasing from its inactive state as the temperature increases.
The enzyme is at its most active state at optimum/optimal temperature (the temperature of which enzyme is most active).
The enzyme activity decreases as it is exposed to temperature above the optimum/optimal temperature. And at extreme temperature, the enzyme stopped because they are denatured.
pH
The enzyme activity is increasing from its inactive state as the pH (acidity/alkalinity) increases.
The enzyme is at its most active state at optimum/optimal pH (optimum acidity/optimum alkalinity).
The enzyme activity decrease when it is exposed to above the optimum/optimal pH. And at extreme pH (too acidic/too alkaline), the enzyme stopped because they are denatured.
Most enzymes work best at neutral pH.
Some enzymes work best at acidic pH.
Some enzymes work best at alkaline pH.
Structured Questions Worked Solutions
1. Explain, with reasons and examples, how the biological activity of an enzyme may be affected by:
a. changes in pH; and
b. increasing temperatures.
Solution
a. Enzymes arc sensitive to acidity or alkalinity of a solution. Some work best in acidic conditions, for example, pepsin in the stomach, whereas others work best in alkaline conditions, for example pancreatic amylase. Enzymes are proteins in nature. Extreme changes in pH denature the enzyme. When an enzyme is denatured, it loses its active site configuration and its biological activity thereby decreases.
b. Enzymes work best under optimum temperature, which is 37ºC for most enzymes found in our body. A high temperature increases the kinetic energy supplied to the reacting molecules, which then increases the rate of collision between substrates and enzymes. The rate of the reaction increases up to the optimum temperature. Beyond the optimum temperature, an enzyme, being protein in nature, will be denatured and will lose its active site configuration. The rate of biological reaction will therefore decrease.
2a. Describe the major properties of enzymes.
2b. Discuss the mode of action of an enzyme in terms of active site, enzyme-substrate complex, activation energy and enzyme specificity.
Solution
a. Enzymes are highly specific in action. They are mainly made up of proteins. Enzymes alter the rate of chemical reactions without themselves being changes at the end of the reaction. Small amounts of enzymes are capable of catalysing a large number of reactions. Enzymes work within a narrow range of conditions, such as they have an optimum working temperature and beyond a certain temperature, they are denatured. Enzymes are also affected by the acidity/alkalinity of the solutions in which they act.
b. An enzyme is a catalyst. It acts on a substrate and converts it into a product. The binding of a substrate to the active site of an enzyme is specific in nature. A substrate fits into an enzyme's active site like how a key fits into a lock, forming an enzyme-substrate complex. An enzyme lowers the activation energy needed for a reaction. Activation energy is the energy needed to start a chemical reaction.