In this article, you will learn about the factors that affect an enzyme's action. But before proceeding to discuss the factors, first, let us recall what are enzymes.

What are Enzymes?

Enzymes refer to the proteins that play the role of biological catalysts. It means that they speed up the chemical reactions inside our body, but in the process of doing so, they don't get used up themselves. We use the term "biological catalyst" for enzymes because they are catalysts made up of living cells.

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Why Enzymes are Needed?

Enzymes play a vital role in speeding up the metabolic reactions in all living organisms. These reactions are essential for keeping an organism alive. For instance, if we do not have digestive enzymes in our body, then we would take two to three weeks to digest one meal. Due to enzymes, we are able to digest our meal in around four hours.

How Do Enzymes Work?

An enzyme creates products by working on a substrate. The active site of an enzyme and its substrate are complementary in shape. An enzyme works on a single substrate only. It means that enzymes are substrate-specific. Enzyme-substrate complexes are produced when enzymes and substrates collide with each other.  After this collision, the substrates are broken down or in a few cases, they are built up. In addition to the breakdown of substrates, the products are also released after the collision. After that, the enzyme is free to act again. This theory is referred to as the "lock and key model". This model elucidates why each enzyme works on a single substrate only. For instance, the active site of the enzyme amylase is only complementary to starch. Hence, amylase will break down starch only, rather than any other molecules such as protein or fat.

Factors Affecting Enzyme Activity

The factors which affect the enzyme activity are:

  • Temperature
  • Effect of PH
  • Effect of concentration which includes both substrate and enzyme concentration

Factor 1: Temperature

Extreme high and low temperatures affect the enzyme action in different ways.

At low temperatures

At low temperatures, the number of collisions between the substrate and the enzyme is minimized due to the decrease in molecular movement. In other words, this reaction becomes slow.

At high temperatures

Extremely high temperatures distort the shape of the enzyme's active site. This will result in reduced activity or prohibit the enzyme from working. Consequently, the denaturation of the enzyme will occur.

We can also understand the effect of high temperature on enzyme action in our bodies by focusing on the nature and composition of enzymes. Enzymes are proteins that are formed by chains of amino acids joined with each other. This chain has several folds and twists. In other words, we can say that each enzyme is constituted of proteins made up of these twisting and folding amino acids. These twists and folds impart a unique shape or structure to each enzyme. This structure is maintained by weak forces between the amino acid molecules in the chain. High temperatures break these forces and the enzyme's active site alters its shape. When the shape will change, then the substrate will no longer fit into the enzyme's active site. Consequently, the rate of the reaction will be affected, or the reaction will stop completely.

Hence, enzymes work best at a specific temperature only. Our body is maintained at 37^0 C and our enzymes work best at this temperature. However, this is not the right temperature for all other living organisms.

Factor 2: The Effect of pH

pH also affects the enzymes. Just like high temperatures, changing the pH of the enzyme's surroundings will alter the shape of its active site. Several amino acids in an enzyme molecule have a charge. Inside an enzyme molecule, positively and negatively charged amino acids will be attracted towards each other. This will result in the folding of the enzyme molecule, its shape, and the shape of its active site.

When the pH changes, the charges on the amino acid molecules get affected. There may not be any attraction between the amino acids resulting in the change of the shape and active site of the enzyme. Extreme pH also results in the denaturation of enzymes. Usually, this denaturation is not permanent.

Optimum pH in Our Digestive System

  • Enzymes not only work inside but also outside our cells. For example, the cells in our digestive system are kept at 7.0 pH to 7.4 pH. Cellular enzymes will show optimum performance within this pH range. Different enzymes are produced in different parts of our digestive systems. This means that these parts would have varying pHs.
  • The optimum pH in our stomach is created when hydrochloric acid is secreted
  • The optimum pH is duodenum is produced when sodium hydrogen carbonate is secreted
  • Although the optimum pH for the majority of enzymes is 7, however, some enzymes that are produced in acidic conditions may have a lower optimum pH of 2. On the other hand, the enzymes produced in alkaline conditions, such as in the duodenum, can have a higher optimum pH, i.e. 8 or 9.

Factor 3: Effects of Concentration

Substrate Concentration

Enzymes will perform best if there is a lot of substrate available. The enzyme activity increases with the increase in the concentration of substrate. It means that if there is plenty of substrate available, then enzymes can break down more substrate.

While an increase in the substrate concentration enhances the enzyme activity, however, it does not happen without a limit. This is due to the fact that even if a lot of substrate is available, the enzymes cannot work any faster. So, when the amount of substrate surpasses the amount of enzymes, then no more substrate can be broken down. In other words, we can say that the enzyme molecules are saturated with the substrate. The additional substrate molecules cannot react until the substrate that has already bonded with enzymes has reacted and the enzyme has been released.

Enzyme Concentration

The increase in the concentration of the enzyme increases its activity. It means that in the presence of more enzymes, more substrates will be broken down.

Just like substrate concentration, there is also a limit to the increase in enzyme activity due to an increase in enzyme concentration. In other words, we can say that when the amount of available enzyme surpasses the amount of substrate, then no more substrate can be broken down.

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Rafia Shabbir