Enzymes Session I

Enzymes are large, complex proteins made up of long chains of amino acids. They are globular proteins. As we know, proteins are built from long chains of amino acids. The specific sequence of these amino acids determines the structure and function of enzymes. Enzymes carry out chemical reactions in our body. They help by increasing the speed at which chemical reactions take place. Enzymes are very sensitive to changes in temperature. Enzymes of our body function at temperature of about thirty seven Celsius. Any small or large change in temperature effects the functioning of enzymes.

Enzymes consist of both protein and non-protein components, including Cofactors and coenzymes. The protein component of enzymes is called Apoenzyme. Cofactors are non-protein molecules or ions that are required for the proper functioning of particular enzymes. Coenzymes are small, non protein molecules that are loosely associated with the enzyme. They are carriers of chemical groups or electrons during enzymatic reactions. The complete functional enzyme is called Holoenzyme.

There is a special region within the enzyme where the chemical reaction catalyzed by the enzyme takes place. This region is called the active site. Active site is a region within the three dimensional structure of enzyme that specifically binds to the substrate. Substrate is a molecule or compound upon which an enzyme acts and converts it into product. The active site is highly specialized and precisely shaped to accommodate the specific substrate molecules.

Intracellular enzymes are proteins that are located inside cells. These proteins perform essential tasks inside cells. They are like tiny molecular machines that help with various important processes within the cell. These processes include breaking-down large molecules into smaller ones to produce energy and constructing new molecules for growth and repair. These enzymes are produced by the cell itself based on its needs.

Think of intracellular enzymes as workers that are employed within the cell. Intracellular enzymes are located in specific compartments within the cell, where they can perform their designated tasks effectively. They are responsible for carrying out specific jobs, such as speeding up chemical reactions or transforming one molecule into another. Examples of intracellular enzymes include DNA polymerase, ATP synthase and catalase.

Extracellular enzymes are enzymes that are produced and released by cells into the surrounding environment. Intracellular enzymes remain within the cell and catalyze reactions inside the cytoplasm or organelles. Extracellular enzymes function outside the cell. They are involved in breaking-down complex macromolecules, such as proteins, carbohydrates, and lipids, into simpler components. These simpler components can be easily absorbed and utilized by the organism.

The secretion of extracellular enzymes allows organisms to access nutrients and energy sources that would otherwise be inaccessible. For example, many bacteria produce extracellular enzymes that break-down complex polysaccharides found in plant cell walls. This enables the bacteria to utilize these carbohydrates as a nutrient source. Similarly, fungi release extracellular enzymes to decompose organic matter in the environment. This aids in nutrient recycling.

As we know, enzymes are protein molecules that act as catalysts by speeding up chemical reactions in living organisms. The mechanism of Enzyme Action involves several steps. First, the substrate molecule binds to active site of enzyme. The active site has a unique shape that allows it to recognize and bind to the specific substrate. When the substrate binds to the active site, an enzyme substrate complex is formed.

The enzyme substrate complex is stabilized by temporary weak interactions, such as hydrogen bonds and van der Waals forces. When the enzyme and substrate come together, the enzyme changes its shape slightly. This change allows specific parts of the enzyme, called amino acid residues, to get nearer to the substrate. This closeness helps the reaction happen more easily.

Inside the active site of the enzyme, the activation energy needed for the reaction is reduced. Activation energy is the amount of energy that needs to be supplied to a chemical reaction in order for it to proceed. The enzyme does this by creating the ideal conditions for the reaction to occur. As a result the reaction happens faster and more efficiently.

The reaction leads to the transformation of the substrate into one or more products. They have different chemical properties than the substrate. These products are released from the active site. Once the products are released, the enzyme returns to its original conformation. It is now ready to bind to new substrate molecules. Enzymes are not consumed or permanently altered during the reaction. This allows them to be used repeatedly.

Have you ever wondered how enzymes can do their jobs so precisely? This is due to specificity of enzymes. Enzyme specificity refers to the ability of enzymes to selectively recognize and bind to specific molecules. The active site of enzymes is designed in way to perfectly fit and bind to specific substrate. The active site contains special chemical groups that can form hydrogen bonds and electrostatic interaction with substrate. These interactions help the enzyme recognize its target and establish a strong bond.

The lock and key hypothesis is a concept that helps us understand how enzymes interact with their specific substrates. It says that the active site of an enzyme is like a lock, and the substrate is like a key that fits perfectly into that lock. According to this hypothesis, the active site of an enzyme has a specific shape and chemical properties that precisely fit the shape and properties of its substrate. This allows the enzyme to selectively bind to and interact with only its specific substrate. It is similar to a lock that can be opened only by the correct key.

When the substrate fits into the active site, it forms a temporary bond with the enzyme. This allows the enzyme to do its job and carry out chemical reactions on the substrate. It's like the lock and key coming together to unlock something. This hypothesis helps us understand why enzymes are so good at their jobs. They can pick out the correct molecules to work on because their active sites are shaped exactly for those molecules.

Unlike lock and key hypothesis, the induced fit hypothesis provides a better explanation of binding of substrate to active site. According to Induced fit hypothesis, active site of an enzyme is not a rigid structure. It is rather a flexible region that can change its shape upon substrate binding. Initially, the active site might not perfectly fit to the substrate. But when the substrate enters the active site, the active site changes its shape to perfectly fit the substrate. Can you tell which hypothesis best describes the functioning of enzymes?.