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

The correct pair is (d) haemoglobin, cytochromes.

Step 1: Understanding the Task

We need to identify the pair of species that both contain iron. This involves recalling what each species contains and their components.

Step 2: Analyzing Each Option

Examine each pair of species: (a) Nitrogenase typically contains iron and molybdenum; cytochromes contain iron within their heme groups. (b) Carboxypeptidase contains zinc; haemoglobin contains iron. (c) Haemocyanin contains copper; nitrogenase contains iron. (d) Haemoglobin contains iron; cytochromes contain iron within their heme groups.

Step 3: Identifying the Correct Pair

Identify the option where both species in the pair explicitly contain iron: After analyzing the components, option (d) haemoglobin and cytochromes both contain iron.

Key Concepts

Haemoglobin

Haemoglobin is a vital iron-containing protein found in red blood cells. It plays a crucial role in transporting oxygen from the lungs to different parts of the body and returning carbon dioxide from the tissues back to the lungs. This protein has a distinctive red color, which is why blood appears red.
Haemoglobin is made up of four subunits, each containing a heme group. The heme group includes an iron ion ( abla) that binds oxygen. The iron in haemoglobin allows it to efficiently capture oxygen molecules and release them where needed.

• Each molecule of oxygen binds to the iron atom in the haem group's porphyrin ring.
• The binding of oxygen causes a conformational change in haemoglobin, enhancing its ability to transport oxygen.
• Iron plays an essential role in maintaining the structure and function of haemoglobin.

By understanding the structure of haemoglobin, we grasp how critical iron is to its functionality and why haemoglobin is featured in coordination chemistry discussions.

Cytochromes

Cytochromes are essential iron-containing proteins found within the cells that are involved in electron transfer processes. Integral to cell respiration and photosynthesis, cytochromes aid in ATP production by facilitating the transport of electrons in the electron transport chain.
These proteins contain heme groups similar to haemoglobin, with iron as a central feature enabling electron mobility.

• Cytochromes play a key role in mitochondrial respiration where they act as electron carriers.
• The iron within the heme group alternates between different oxidation states, allowing electron transfer.
• Important examples of cytochromes include cytochrome c, which is pivotal in the electron transport chain.

This consistent electron shuffling facilitated by iron's versatile oxidation states underscores why both cytochromes and haemoglobin are central to essential biological processes.

Iron-containing Proteins

Iron-containing proteins, as suggested by their name, house iron within their structures, which is crucial for a myriad of biological functions. These proteins encompass a wide range, from enzymes involved in DNA synthesis to those regulating oxygen transport.

• Iron-sulfur proteins participate in electron transfer and enzymatic functions.
• Transferrin is a protein that binds and transports iron in the bloodstream, essential for regulating iron levels.
• Iron's ability to catalyze redox reactions makes it indispensable in the realms of metabolism and cell respiration.

Understanding iron-containing proteins reveals how iron's unique chemical properties support life on multiple fronts.

Nitrogenase

Nitrogenase is a remarkable enzyme that catalyzes the conversion of atmospheric nitrogen ( abla N_2) into ammonia ( abla NH_3), a process known as nitrogen fixation. This process is vital for providing a usable form of nitrogen to plants.
Nitrogenase is complex and its activity hinges on the presence of both iron and molybdenum in its structure.

• Iron and molybdenum are found in the FeMo-cofactor, the active site of nitrogenase.
• Through this cofactor, electrons are transferred to nitrogen, reducing it to ammonia.
• Nitrogenase action is crucial for agricultural productivity and ecological balance.

The enzyme highlights the versatility of iron in facilitating essential biochemical transformations, further showcasing coordination chemistry’s role in life's processes.

Haemocyanin

Haemocyanin is an oxygen-carrying protein similar in function to haemoglobin but distinct in composition. Found in the blood of many arthropods and mollusks, it uses copper instead of iron for binding oxygen.
This copper-containing protein imparts a blue color to the blood, contrasting the red hue provided by haemoglobin’s iron.

• Haemocyanin is less efficient than haemoglobin at oxygen transport, fitting the needs of cold-blooded animals.
• Oxygen binds directly to copper ions within haemocyanin.
• Its efficiency varies significantly with temperature change, adapting the organism’s oxygen supply to external conditions.

Haemocyanin's reliance on copper rather than iron illustrates the diverse strategies of oxygen transport across different species, offering intriguing insights into evolution and adaptation.