Enzymes – Session 3

We have already learned the effect of the temperature on the activity of the enzymes. We also know that the enzymes work best at the optimum temperature. There is another factor that affects the activity of the enzymes. That factor is the pH. But, what is pH?.

Well, think of pH as a special scale that measures how acidic or basic something is. Imagine you have a lemon and a cake of soap. Lemons are sour, right? That is because they are acidic. So, they have a low pH.

On the other hand, soap is slippery and not sour at all. It is basic. So it has a high pH. The pH scale goes from zero to fourteen. The pH value of seven is considered as neutral. If the pH of a solution is less than seven, then the solution is acidic. If the pH of the solution is greater than seven, then the substance is considered as basic.

The enzymes are a bit picky. They like to work in particular pH levels that make them comfortable. Imagine you are a singer. You sound the best when the music is just-right and not too-fast or too-slow. Similarly, the enzymes work best when the pH is just-right for them.

If the pH is too-high or too-low, they might not work as well. It is same as you might not sing at your best if the music is too-fast or too-slow. Imagine the enzyme is like a chef cooking in the kitchen. If the kitchen is too-hot or too-cold, the chef might not cook the food perfectly. In the same way, if the pH is too-high or too-low, the enzyme might not do its job properly.

Each enzyme has its favorite pH range. The pH range at which enzymes work best is called the optimum pH range range. For example, pepsin is the enzyme that works in our stomach. It helps in breaking-down the food. It works best in a very acidic environment, with an optimum pH range of around 1.5 to 2.5.

When we eat food, our stomach releases acid. The mixture of food in our stomach becomes acidic. The pH drops-down to optimum pH range for the pepsin. There is also the enzyme in our saliva. This enzyme is called the salivary amylase. The salivary amylase works best around a neutral pH.

The enzyme denaturation refers to the distortion of structure of the enzyme. Imagine you have a bouncy toy, like a ball. It is round-shaped and bounces all over the place. Now imagine your ball getting squished or twisted. What happens to the ball? It stops bouncing like it used to, right? Enzymes also have a specific shape that helps them do their jobs perfectly. But if we change their shape, they might not work the way they are supposed to.

There are a few things that can cause the enzyme denaturation. One of them is heat. Think about melting a crayon. It gets all soft and changes shape. If we heat up the enzyme beyond a particular value, it can also change shape and stop working.

If we increment the temperature beyond the optimum range, the shape of the active site of the enzyme changes. Now the substrate can not fit into the active site of the enzyme. As a result the reaction will not happen. That is why the optimum temperature range is necessary for the maximum efficiency of the enzymes.

For a reaction to occur, the substrate must collide with the enzyme. The collision between the enzyme and the substrate must be perfect. For example, if the substrate collides with the enzyme in correct direction, then enzyme substrate complex will form. If the collision is imperfect then the reaction would not occur.

The frequency of effective collisions refers to the number of perfect-collisions that take place between the enzymes and the substrates. This leads to the formation of products. If the frequency of effective collisions is greater, then greater number of substrate molecules will be converted into the products. This increases the speed of the reaction.

The frequency of effective collisions depends on the concentration of reactants and the enzymes. Frequency of collisions will become higher if we increment the number of substrate molecules. Similarly, if we increment the number of enzymes then the frequency of collision will become greater. Less number of substrate molecules and enzymes will result in low frequency of collision.

The frequency of effective collisions also depends on the temperature. If we increment the temperature within the optimum range, the substrate and enzymes will get high energy. They will move and collide with each other more often. This will result in rise in the frequency of effective collisions.