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: Introduction to Coordination Compounds

Coordination compounds play a crucial role in various biological systems. Examples include chlorophyll in plants, haemoglobin in blood, vitamin B12, and enzymes like carboxypeptidase-A. Each of these compounds is characterized by a central metal atom that coordinates with surrounding ligands.

Step 2: Analyze Chlorophyll

Chlorophyll is a green pigment responsible for the absorption of light to provide energy for photosynthesis in plants, algae, and some bacteria. Chlorophyll contains magnesium (Mg), not calcium. Thus, statement (a) is incorrect as it wrongly states chlorophyll contains calcium.

Step 3: Analyze Haemoglobin

Haemoglobin is a protein in red blood cells responsible for transporting oxygen in the blood of vertebrates. It contains iron (Fe) as part of its structure, held within the heme group. Statement (b) is correct.

Step 4: Analyze Cyanocobalamin

Cyanocobalamin is a synthetic form of Vitamin B12, which is essential for normal blood formation and neurological function. It contains cobalt (Co) at its core. Thus, statement (c) is correct.

Step 5: Analyze Carboxypeptidase-A

Carboxypeptidase-A is a zinc-containing enzyme that is critical for digestion in animals. It requires zinc (Zn) to function properly, making statement (d) correct.

Step 6: Conclusion: Identify Incorrect Statement

From the analysis, statement (a) about chlorophyll containing calcium is incorrect. It should have mentioned magnesium instead.

Key Concepts

Biological Systems

Biological systems are complex networks of biologically relevant entities and processes. They are critical for sustaining life and maintaining health. Coordination compounds, which are molecules with a central metal atom bound to surrounding ligands, have pivotal roles in these systems.
For instance:

• Chlorophyll in plants absorbs sunlight for photosynthesis.
• Haemoglobin in blood transfers oxygen throughout the body.
• Vitamin B12 supports blood formation and neurological function.
• Enzymes like carboxypeptidase-A facilitate digestion.

Understanding coordination compounds expands our knowledge of how biological systems function and sustain life.

Chlorophyll

Chlorophyll is the pigment that gives plants their green color and is vital for photosynthesis. During photosynthesis, chlorophyll absorbs light energy, which is converted into chemical energy. This process is crucial for the survival of plants and, indirectly, all life on Earth. Chlorophyll contains a central magnesium ion coordinated by a porphyrin ring.

• It captures light primarily in the blue and red wavelengths.
• Magnesium (Mg) at its core plays a crucial role in maintaining the structure essential for its function.
• Contrary to some misconceptions, chlorophyll does not contain calcium.

Thus, it is important in both energy production and as a component of the ecosystem's oxygen cycle.

Haemoglobin

Haemoglobin is a protein complex essential for transporting oxygen from the lungs to other parts of the body, and for facilitating the return of carbon dioxide to the lungs for expulsion.
It is a tetramer, composed of four subunits, each containing a heme group that holds an iron ion.

• The iron (Fe) ion is crucial for oxygen binding.
• Each molecule of haemoglobin can carry four oxygen molecules.
• This oxygen-carrying function is vital for cellular respiration.

Without efficient haemoglobin, our bodies would not get enough oxygen to sustain vital processes.

Vitamin B12

Vitamin B12, or cyanocobalamin, is a water-soluble vitamin crucial for maintaining healthy nerve cells and producing DNA and red blood cells.
Its structure includes a central cobalt ion, uniquely characterized by a coordination with a corrin ring.

• The cobalt ion is essential for the vitamin's biological activity.
• It assists in the body's utilization of folic acid and helps in the synthesis of new cells.
• A deficiency in vitamin B12 can lead to anemia and neurological issues.

This vitamin illustrates how coordination chemistry plays a role in nutrition and health.

Coordination Chemistry

Coordination chemistry examines the complexes formed between metal ions and ligands. These compounds have diverse structures and functions, influencing numerous biological processes.

• Central metal ions can vary, including Mg, Fe, Zn, and Co, as seen in chlorophyll, haemoglobin, enzymes, and vitamin B12 respectively.
• Ligands are typically organic molecules or ions that surround the metal ion to stabilize the complex.
• These complexes can bond and interact with biological molecules, affecting pathways and reactions.

By studying coordination chemistry, scientists gain insights into how metals are used and regulated in living organisms, enhancing our comprehension of life at the molecular level.