Problem 64 - A Complete Resource Book in Chemistry for JEE Main

Question

The efficiency of an enzyme to catalyse a reaction is due to its capacity to (a) reduce the activation energy of the reaction (b) form strong enzyme substrate complex (c) decrease the bond energy of all substrate molecules (d) increase the free energy of the catalyst substrate reaction (e) alter the substrate geometry to fit into the shape of the enzyme molecule.

Step-by-Step Solution

Answer

(a) reduce the activation energy of the reaction.

Step 1: Understanding the Role of Enzymes

To solve this question, we first need to understand what enzymes do. Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy needed for the reaction to occur. This means they make it easier for the reaction to take place.

Step 2: Analyzing the Options

We now look at the options. Option (a) states that enzymes reduce the activation energy of the reaction, which matches our understanding of how enzymes work. Option (b) seems correct in that enzymes do form enzyme-substrate complexes, but this alone doesn't directly explain how they catalyze reactions. Options (c), (d), and (e) don't accurately describe the primary catalytic function of enzymes.

Step 3: Selecting the Correct Answer

Comparing all the options, the most direct reason for the enzyme's ability to catalyze a reaction is its ability to reduce the activation energy of the reaction. This makes option (a) the correct choice, as reducing activation energy is the core function of enzyme catalysis.

Key Concepts

Activation Energy

Activation energy is a foundational concept in chemistry and biology that refers to the minimum amount of energy required for a chemical reaction to proceed. In simple terms, imagine needing a certain push to get a boulder rolling down a hill. Similarly, molecules need a certain amount of energy to break existing bonds and form new ones, which leads to a chemical reaction.

Enzymes, which are proteins acting as catalysts, play a significant role by lowering this activation energy. By reducing the energy barrier, enzymes allow reactions to happen more quickly and efficiently. This is why they are incredibly important for speeding up the processes necessary for life.

In biological systems, reactions must occur at a speed conducive to life. By lowering activation energy, enzymes ensure that these reactions proceed at rates that allow organisms to thrive in changing environments.

Enzyme-Substrate Complex

The enzyme-substrate complex is fundamental to understanding how enzymes work. Think of the enzyme as a lock and the substrate as a key. When a specific substrate binds to the enzyme's active site (like a key fitting into a lock), an enzyme-substrate complex is formed.

• The substrate is the molecule upon which the enzyme acts.
• The active site is the part of the enzyme where substrate binding occurs.

Once this complex is formed, the enzyme can perform its catalytic function. This is where the magic happens, as forming the complex results in a "transition state." This state is more energetically favorable, meaning it requires less activation energy to convert the substrate into products.

The specificity of enzymes is due to their unique active sites. Only substrates with a complementary shape and chemical structure can fit and form a complex, which is why enzymes are highly selective for their substrates.

Biological Catalysts

Enzymes are considered biological catalysts because they speed up chemical reactions without being consumed in the process. Unlike chemical catalysts, enzymes operate under mild conditions, such as standard temperature and neutral pH, which is why they are so efficient for living organisms.

• They can be reused multiple times, which increases efficiency.
• Enzymes are specific, meaning each type of enzyme only catalyzes one specific type of reaction or reacts with a specific substrate.

This specificity and reusability are central features that make enzymes indispensable in biological systems. By regulating the speed of biochemical reactions, enzymes control the metabolic pathways that sustain life.

Their role as biological catalysts is why they are key to processes ranging from digestion to DNA replication. In each of these processes, enzymes lower the activation energy, allowing critical reactions to occur rapidly and efficiently in cells.