Problem 153 - A Complete Resource Book in Chemistry for JEE Main

Question

Coordination compounds have great importance in biological systems. In this context, which of the following statements is incorrect? (a) chlorophylls are green pigments in plants and contain calcium (b) haemoglobin is the red pigment of blood and contains iron (c) cyanocobalamin is vitamin \(\mathrm{B}_{12}\) and contains cobalt (d) carboxypeptidase-A is an enzyme and contains zinc

Step-by-Step Solution

Answer

Statement (a) is incorrect; chlorophyll contains magnesium, not calcium.

Step 1: Understanding Coordination Compounds

Coordination compounds consist of a central metal atom or ion bonded to surrounding molecules or anions, known as ligands. These compounds are crucial in biological systems due to their roles in processes such as enzyme actions, oxygen transport, and photosynthesis.

Step 2: Evaluating Statements A to D

We will evaluate each statement to see if the description accurately matches the role or composition of the compounds mentioned: 1. **Statement (a)**: Chlorophylls - Chlorophylls are the green pigments responsible for photosynthesis in plants; they contain magnesium, not calcium. 2. **Statement (b)**: Haemoglobin - It is the red pigment in blood, transporting oxygen, and contains iron in its structure. 3. **Statement (c)**: Cyanocobalamin - Known as vitamin B12, it plays a vital role in DNA synthesis and red blood cell formation, and contains cobalt. 4. **Statement (d)**: Carboxypeptidase-A - This enzyme functions in protein digestion and contains zinc.

Step 3: Identifying the Incorrect Statement

From the evaluation: - Statement (a) is incorrect as chlorophyll contains magnesium, not calcium. - Statements (b), (c), and (d) are correct as they accurately describe the composition and role of each compound.

Key Concepts

Biological Systems

Biological systems are composed of complex interactions between various biomolecules and elements. Coordination compounds, which play an integral role in these systems, consist of metal ions bonded to molecules, known as ligands. These compounds are involved in numerous biological processes. For instance, metal ions such as iron, magnesium, and cobalt are central to the function and structure of vital biomolecules.
Metal ions in coordination compounds can catalyze biochemical reactions and stabilize complex structures. This capability is crucial for maintaining the delicate balance within biological systems. Without these processes, essential functions such as oxygen transport and energy production would be impossible. Let's delve into some specific biological roles coordination compounds fulfill.

Enzyme Actions

Enzymes act as biological catalysts that metabolize substrates rapidly and efficiently. Coordination compounds are often a key component of these enzymes. For instance, the enzyme carboxypeptidase-A contains zinc and is responsible for breaking down proteins during digestion.
The presence of a metal ion like zinc in this enzyme allows for stabilization of the substrate and activation of water molecules, which are essential for hydrolysis reactions. This function enables the enzyme to cleave peptide bonds efficiently.

• Stability: Metal ions provide structural stability to the enzyme.
• Activation: They facilitate the activation of oxygen molecules required in reactions.
• Efficiency: Accelerate enzymatic activity without altering the enzyme's structure.

Understanding these actions is vital as enzymes are fundamental to numerous biological processes, including DNA replication and energy metabolism.

Photosynthesis

Photosynthesis is a process through which plants convert light energy into chemical energy. This process is made possible by chlorophyll, a coordination compound containing magnesium. Chlorophyll absorbs sunlight, which initiates the transformation of water and carbon dioxide into glucose and oxygen.
Chlorophyll's complex structure allows it to capture light energy effectively. The central magnesium ion in chlorophyll is crucial for this function, facilitating the transfer of energy through electron excitation.
Chlorophyll ensures that plants can carry out photosynthesis efficiently, supporting oxygen production and growing their own food. This is not just crucial for plants but also forms the foundation of the food chain for most life on Earth. Coordination compounds in chlorophyll highlight the intricate balance within nature where a single metal ion can support monumental processes.

Oxygen Transport

Oxygen transport is a life-sustaining process facilitated by haemoglobin in the blood. Haemoglobin is a coordination compound with iron at its core, which plays a key role in binding and releasing oxygen molecules efficiently.
This iron ion enables haemoglobin to attach oxygen in the lungs and transport it throughout the body, ensuring that every cell receives the necessary oxygen for metabolic processes.
Once at the tissues, haemoglobin releases oxygen and picks up carbon dioxide, returning it to the lungs for release. Without this precise system, our bodies would be unable to perform essential functions that require energy.
Haemoglobin’s structure, with its central iron ion, exemplifies how coordination compounds are indispensable in biological systems, ensuring life continues to flourish with each breath we take.