WHAT ARE ENZYMES?
Enzymes are biological catalysts made of protein. They alter (speed up) the rate of chemical reactions without themselves being chemically changed at the end of the reactions.
(Analogy: It is just like walking on foot or driving to KB. Walking on foot to KB (slower) is just like a reaction not catalyzed by an enzyme whereas driving to KB (faster) is just like an enzyme catalyzed reaction. Note that in this analogy the car is the enzyme which facilitates the journey just like an enzyme speeding up a chemical reaction).
How do enzymes really work? This can be explained by means of the LOCK AND KEY hypothesis. The following figures show this hypothesis.
Catabolic Reaction (a breaking down reaction) - In this type of reaction, an enzyme helps to facilitate the breakdown of a large molecule into smaller molecules. Digestion of starch into maltose is an example of a catabolic reaction. In this example, starch is broken down by an enzyme called amylase. Another example is the breakdown of maltose into glucose by an enzyme called, maltase.
Anabolic reaction (a building up reaction) - In this type of reaction, larger molecules are made from smaller molecules with the help of enzymes. For example, hundreds of glucose molecules might be joined together end to end to form a long molecules of starch and this process is catalysed by enzymes.
Note: In both types of reaction, the enzymes are not chemically changed and can be used over and over again. Hence a little enzyme can react with many substrates.
ENZYMES AND TEMPERATURE
A rise in temperature increases the rate of most chemical reactions and a fall slows them down. In many cases, a rise of 10 degree C will double the rate of reaction in a cell. This is equally true foe enzyme controlled reactions, but above 50 degree C, the enzymes, being proteins are denatured and stop working. When enzymes are denatured, substrates molecules will not be able to fit in into the active site of the enzymes. Hence reactions cannot take place. The graph below shows that enzymes will perform very well at optimum temperature. (Note: once denatured due to temperature, the enzymes will be permanently damaged and cannot be used again)
This is one of the reasons why organisms may be killed by prolonged exposure to high temperatures. The enzymes in their cells are denatured and the chemical reactions proceed too slowly to maintain life.
Enzymes are biological catalysts made of protein. They alter (speed up) the rate of chemical reactions without themselves being chemically changed at the end of the reactions.
(Analogy: It is just like walking on foot or driving to KB. Walking on foot to KB (slower) is just like a reaction not catalyzed by an enzyme whereas driving to KB (faster) is just like an enzyme catalyzed reaction. Note that in this analogy the car is the enzyme which facilitates the journey just like an enzyme speeding up a chemical reaction).
How do enzymes really work? This can be explained by means of the LOCK AND KEY hypothesis. The following figures show this hypothesis.
Catabolic Reaction (a breaking down reaction) - In this type of reaction, an enzyme helps to facilitate the breakdown of a large molecule into smaller molecules. Digestion of starch into maltose is an example of a catabolic reaction. In this example, starch is broken down by an enzyme called amylase. Another example is the breakdown of maltose into glucose by an enzyme called, maltase.
Anabolic reaction (a building up reaction) - In this type of reaction, larger molecules are made from smaller molecules with the help of enzymes. For example, hundreds of glucose molecules might be joined together end to end to form a long molecules of starch and this process is catalysed by enzymes.
Note: In both types of reaction, the enzymes are not chemically changed and can be used over and over again. Hence a little enzyme can react with many substrates.
ENZYMES AND TEMPERATURE
A rise in temperature increases the rate of most chemical reactions and a fall slows them down. In many cases, a rise of 10 degree C will double the rate of reaction in a cell. This is equally true foe enzyme controlled reactions, but above 50 degree C, the enzymes, being proteins are denatured and stop working. When enzymes are denatured, substrates molecules will not be able to fit in into the active site of the enzymes. Hence reactions cannot take place. The graph below shows that enzymes will perform very well at optimum temperature. (Note: once denatured due to temperature, the enzymes will be permanently damaged and cannot be used again)
This is one of the reasons why organisms may be killed by prolonged exposure to high temperatures. The enzymes in their cells are denatured and the chemical reactions proceed too slowly to maintain life.
ENZYMES AND pH
Acid or alkaline conditions alter the chemical properties of proteins including enzymes. Most enzymes work best at a particular level of acidity or alkalinity (pH). Examples: Pepsin in the stomach works well at pH 2 and amylase in the saliva works well at pH 7. (The pH at which enzymes work best is called optimum pH)
Although changes in pH affect activity of enzymes, these effects are usually reversible (unlike the effect of temperature). Extremes of pH however may denature some enzymes irreversibly.
Acid or alkaline conditions alter the chemical properties of proteins including enzymes. Most enzymes work best at a particular level of acidity or alkalinity (pH). Examples: Pepsin in the stomach works well at pH 2 and amylase in the saliva works well at pH 7. (The pH at which enzymes work best is called optimum pH)
Although changes in pH affect activity of enzymes, these effects are usually reversible (unlike the effect of temperature). Extremes of pH however may denature some enzymes irreversibly.
EFFECTS OF SUBSTRATE AND ENZYME CONCENTRATIONS ON RATE OF REACTIONFrom the following graph, it can be seen that as the substrate concentration increases, the rate of reaction increases initially until the point X is reached. However, further increase in substrate concentration will not increase the rate any further. This is because, after point X, all the enzyme molecules are being saturated or made use of. The same happened when enzyme concentration is increased, the rate of reaction can only increase so much (point Y) but after point Y the rate can no longer increase as all the enzyme molecules are being used in the reaction.
ENZYMES ARE VERY SPECIFIC IN NATURE
This means that a certain enzyme can only react with a certain substrate but not with other substrates. For example, amylase can only catalyse starch but not protein, and likewise, protease can only catalyse proteins but not starch. This is because of the active sites of the enzymes which have complimentary shape with the substrates they react with.
This means that a certain enzyme can only react with a certain substrate but not with other substrates. For example, amylase can only catalyse starch but not protein, and likewise, protease can only catalyse proteins but not starch. This is because of the active sites of the enzymes which have complimentary shape with the substrates they react with.
