Problem 187 - A Complete Resource Book in Chemistry for JEE Main

Question

Identify the correct statement regarding enzymes. (a) Enzymes are specific biological catalysts that cannot be poisoned (b) Enzymes are specific biological catalysts that possess well defined active sites (c) Enzymes are specific biological catalysts than can normally function at very high temperatures (1000\textrm{K} ) ~ (d) Enzymes are normally heterogeneous

Step-by-Step Solution

Answer

Option (b) is correct: Enzymes have well-defined active sites.

Step 1: Understanding Enzymes

Enzymes are highly specific biological catalysts that speed up chemical reactions in living organisms. They are known for working at mild conditions and having very specific active sites for their substrates.

Step 2: Evaluating Option (a)

This option states that enzymes cannot be poisoned. While enzymes are indeed specific biological catalysts, they can be inhibited or poisoned by certain chemicals that interfere with their activity.

Step 3: Evaluating Option (b)

This option states that enzymes have well-defined active sites. This is accurate because enzymes typically have a specific active site where the substrate binds, allowing them to catalyze biochemical reactions selectively.

Step 4: Evaluating Option (c)

This option states that enzymes function at very high temperatures, like 1000 K, which is incorrect. Enzymes generally function within a narrow temperature range and can denature or lose activity at high temperatures.

Step 5: Evaluating Option (d)

This option describes enzymes as normally heterogeneous. Enzymes are not heterogeneous catalysts; they are homogeneous catalysts that function in solutions within cells or organisms.

Step 6: Selecting the Correct Statement

After analyzing each option, the statement that accurately describes enzymes is option (b): Enzymes are specific biological catalysts that possess well-defined active sites.

Key Concepts

Biological Catalysts

Enzymes are fascinating biological catalysts that play a crucial role in facilitating chemical reactions in living organisms. A catalyst, in general, is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change. In biological systems, enzymes take on this role, allowing complex biochemical reactions to occur rapidly at body temperature.

These catalysts are highly efficient, often accelerating reactions by thousands or even millions of times compared to those that occur non-enzymatically. This efficiency is vital for maintaining life, enabling processes such as digestion, metabolism, and DNA synthesis to occur quickly and efficiently.

• Enzymes lower the activation energy of reactions, making it easier for the reaction to proceed.
• They are highly specific, interacting only with particular substrates.

In essence, enzymes are the biological powerhouses that drive the chemistry of life.

Active Sites

The active site of an enzyme is a specific region where substrate molecules bind and undergo a chemical reaction. This area is unique to each enzyme, giving it the specificity needed to recognize its particular substrate.

Inside the active site, a range of interactions occurs, including hydrogen bonding and van der Waals forces. These non-covalent interactions help stabilize the enzyme-substrate complex, allowing the reaction to proceed swiftly and efficiently.

• Active sites are tailor-made to fit their respective substrates, often described as a 'lock and key' model where the enzyme is the lock and the substrate the key.
• Some enzymes change shape around the substrate, a concept known as the 'induced fit' model, enhancing the interaction even further.

By ensuring that the active site is precisely complementary to its substrate, enzymes achieve remarkable specificity in the reactions they catalyze.

Enzyme Inhibition

Enzymes are not entirely indestructible and can be inhibited by various substances. Enzyme inhibitors are molecules that bind to enzymes and reduce their activity. This binding can be reversible or irreversible, affecting how the enzyme functions.

Reversible inhibitors bind to enzymes through non-covalent interactions and can be removed, while irreversible inhibitors form covalent bonds, permanently disabling the enzyme.

• Competitive inhibitors compete with the substrate directly for the active site. By increasing substrate concentration, one can potentially overcome this type of inhibition.
• Non-competitive inhibitors bind to a different site, potentially altering the enzyme's structure and reducing its capability to bind substrates efficiently.

Understanding enzyme inhibition is crucial in fields like pharmacology, where inhibitors are used to regulate enzyme activity and treat diseases.

Temperature Sensitivity in Enzymes

Enzymes exhibit a significant sensitivity to temperature. Most enzymes function optimally within a specific temperature range, beyond which their activity can decrease sharply.

At low temperatures, the kinetic energy of molecules is reduced, leading to slower reactions. On the other hand, excessive heat can denature enzymes, disrupting hydrogen and ionic bonds and causing the enzyme to lose its precise shape.

• Enzymes from humans usually have an optimal temperature around 37°C, aligning with body temperature.
• Extreme temperature conditions can lead to denaturation, where the enzyme's structure unfolds, losing functionality.

This sensitivity ensures that biochemical reactions occur efficiently at the temperatures required for life and highlights the importance of maintaining stable internal temperatures for homeostasis.