How Do Enzymes Work?

From the smallest virus to the largest oak tree in the planet, enzymes are found. Enzymes are special type of protein that acts as organic catalysts for accelerating the rate of biochemical reactions in living organisms. There are many enzymes found in an organism and each of these enzymes has specific function. There are enzymes that work for food digestion, DNA replication, energy production, protein synthesis, and among other anabolic and catabolic biochemical reactions. Life on earth is impossible without enzymes.

Do you have any idea on how do enzymes work to accelerate biological reactions?  A typical reaction carried out by an enzyme is 100 million times faster than a reaction that didn’t use enzyme. Without enzymes that act as organic catalysts, biological reactions can even be described as “non-existent” because of very slow reaction.

An example of enzyme is rennin. The function of rennin is to coagulate milk (milk curdling) in the stomach of young mammals. Milk curdling is necessary for the milk to stay longer in the stomach for proper digestion. Without rennin, milk easily passes through the stomach and intestines undigested and unabsorbed by the body. Rennin is important for the survival of mammals after birth since milk is their primary food.

This page would not be enough if we are going to write all the enzymes already identified by scientists. It is not necessary to familiarize ourselves with their names but it is very important to learn and understand how enzymes work in biological reactions.

How Do Enzymes Work?

Each enzyme is translated into protein (by ribosomes) using the instruction provided by the genes. Each enzyme is encoded by only one gene. In terms of structure, enzymes differ from each other since they are encoded by different genes. However, enzymes are similar in one aspect: they all have active sites in their structures. It is in the active site where the substrate (the molecule to be modified) binds to form a complex: the enzyme-substrate complex. After successful binding, a biochemical reaction takes place and the substrate is transformed to different molecule(s) called the product(s). The catalytic reaction ends when the products are released, but take note that the enzyme remains unchanged after the reaction. The enzyme can bind to another substrate again and the reaction continues.

Although we already know how an enzyme and substrate reacts with each other, it is not yet clear why an enzyme is “specific” or able to recognize only one kind of substrate. There are two theories proposed by scientists to explain the specificity of enzymes: the lock and key hypothesis and induced-fit hypothesis.

Theories on How Do Enzymes Work – Enzyme Specificity

Enzyme lock and key hypothesis (Image from Wikimedia Commons)Lock and Key Hypothesis – This hypothesis states that the enzyme and substrate are complementary to each other in terms of shape. The shape of the substrate fits to the shape of the enzyme’s active site to form the enzyme-substrate complex. Only substrates that can fit to the active site will be acted upon by the enzyme. The substrate acts like a “key” why the active site acts like a “lock”.

Induced Fit Hypothesis – This hypothesis states that the substrate modifies its structure as it binds to the active site in order to provide an exact position for the enzyme to act upon. In some instances, the active site modifies itself to accommodate the substrate. This is observed in glycosidase enzymes.

Diseases Associated to Enzymes

There are many human diseases that are caused by deficiency or imbalance of enzymes. Among these diseases include diabetes, phenylketonuria, albinism, cystic fibrosis,  MTHFR deficiency, and many more. Some diseases associated to enzymes are caused by genetic mutation. Mutated genes encode for defective enzymes that are unable to catalyze biological reactions.