Problem 61 - A Complete Resource Book in Chemistry for JEE Main

Question

The pair in which both species have iron is (a) nitrogenase, cytochromes (b) carboxypeptidase, haemoglobin (c) haemocyanin, nitrogenase (d) haemoglobin cytochromes

Step-by-Step Solution

Answer

Option (d) haemoglobin and cytochromes.

Step 1: Understanding the Problem

We need to identify which pair of biological molecules both contain iron. Consider each option and the components of the compounds.

Step 2: Analyzing Option (a)

Option (a) lists nitrogenase and cytochromes. Nitrogenase is an enzyme involved in nitrogen fixation and typically contains iron, specifically in the iron-molybdenum cofactor. Cytochromes contain heme groups that have iron, making this option a potential candidate.

Step 3: Analyzing Option (b)

Option (b) lists carboxypeptidase and haemoglobin. Carboxypeptidase is a protease enzyme, but its essential component is zinc, not iron. Haemoglobin contains iron within its heme groups. Thus, this pair does not qualify as both components having iron.

Step 4: Analyzing Option (c)

Option (c) lists haemocyanin and nitrogenase. Haemocyanin, found in some mollusks and arthropods, contains copper, not iron. Nitrogenase contains iron, but since haemocyanin has copper, this pair is not suitable.

Step 5: Analyzing Option (d)

Option (d) lists haemoglobin and cytochromes. Haemoglobin contains iron in the form of heme, and cytochromes also contain iron within their heme structures. Therefore, both molecules in this pair contain iron.

Key Concepts

Nitrogenase

Nitrogenase is a fascinating enzyme that plays a crucial role in the process of nitrogen fixation. This process is essential for converting atmospheric nitrogen gas ( N_2 ) into ammonia ( NH_3 ), a form that plants can utilize to grow. This conversion is vital to life on earth as it enables the assimilation of atmospheric nitrogen into biological molecules.
At the heart of nitrogenase is a special cluster known as the iron-molybdenum cofactor.

• This cofactor is made up of iron and molybdenum atoms.
• The presence of iron is critical for the enzyme's activity, assisting in the electron transfer necessary for reducing nitrogen gas.

Understanding nitrogenase helps us comprehend one of nature's remarkable biochemical processes and highlights the importance of iron in facilitating this vital reaction.

Cytochromes

Cytochromes are a family of proteins found in all living cells and are key players in the electron transport chain. This chain is a series of complexes that transfer electrons from electron donors to electron acceptors via redox reactions. The cytochromes are crucial for cellular respiration, which is the process cells use to generate energy in the form of ATP.
What sets cytochromes apart is their inclusion of heme groups.

• These heme groups contain iron, making cytochromes iron-containing proteins.
• The iron atom within the heme is involved in reversible oxidation and reduction, which is central to its role in electron transport.

This ability to participate in electron transfer makes cytochromes indispensable for energy production in cells.

Haemoglobin

Haemoglobin is a well-known protein found in red blood cells. Its main function is to transport oxygen from the lungs to all parts of the body and carry carbon dioxide back to the lungs for exhalation. Haemoglobin is composed of four subunits, each containing a heme group with iron at its core.
The presence of iron in haemoglobin is pivotal for several reasons:

• Iron binds to oxygen molecules, allowing haemoglobin to transport oxygen efficiently.
• The red color of blood is due to the iron present in haemoglobin.

By understanding how haemoglobin works, we gain insights into how our bodies utilize iron to nourish tissues with oxygen and remove waste gases, maintaining essential life processes.

Iron-containing Enzymes

Iron-containing enzymes are enzymes that have iron atoms within their structure, playing a vital role in various biological reactions. These enzymes can be found across different types of organisms, including bacteria, plants, and animals. Iron's ability to participate in electron transfer reactions makes it an essential component of these enzymes.
Some characteristics of iron-containing enzymes include:

• They participate in oxidation-reduction reactions, helping to convert substrates into more useful forms.
• In addition to nitrogenase and cytochrome, other examples include catalase and aconitase.

Iron-containing enzymes are crucial for maintaining cellular functions and are involved in processes such as detoxification, energy metabolism, and biosynthesis.