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

Question

Which of the following contain prosthetic group? (a) glycoprotein (b) haemoglobin (c) nucleoprotein (d) all of these

Step-by-Step Solution

Answer

Haemoglobin (b) contains a prosthetic group, the heme group.

Step 1: Understanding Prosthetic Groups

A prosthetic group is a non-polypeptide unit that is tightly and permanently attached to a protein and is essential for its biological activity.

Step 2: Examining Glycoproteins

Glycoproteins contain carbohydrate groups covalently attached to polypeptide chains. These carbohydrate groups are not considered prosthetic groups because they don't usually fulfill the tight and permanent attachment required.

Step 3: Examining Haemoglobin

Haemoglobin is a protein that has a heme group tightly bound to it. The heme group, which contains iron, is essential for the protein's ability to transport oxygen, thus acting as a prosthetic group.

Step 4: Examining Nucleoproteins

Nucleoproteins are complexes of proteins with nucleic acids. The nucleic acids don't function as prosthetic groups since they're not permanently attached in a manner that fulfills a critical non-covalent role for a singular protein's function.

Step 5: Determining the Correct Option

Among the options listed, haemoglobin contains a prosthetic group in the form of the heme group. Glycoproteins and nucleoproteins do not meet the criteria for containing prosthetic groups.

Key Concepts

Haemoglobin

Haemoglobin is an essential protein found in red blood cells and plays a crucial role in transporting oxygen from the lungs to the rest of the body. It is composed of four polypeptide chains, each containing a heme group. The heme group is a porphyrin ring that tightly binds an iron ion, which is vital for oxygen transport.
The heme group functions as a prosthetic group within haemoglobin. This means it is a non-polypeptide unit tightly and permanently attached to the protein, crucial for its biological function. Haemoglobin's ability to bind and release oxygen molecules efficiently depends on the presence of this iron-containing heme group. Without it, haemoglobin would lose its functionality in oxygen transport.
Additionally, the heme group's iron ion allows haemoglobin to exhibit its signature red color, which is why blood appears red. This unique property highlights not only the functional but also the aesthetic significance of prosthetic groups like heme in biological systems.

Glycoprotein

Glycoproteins are proteins that have carbohydrate groups covalently bonded to them. These carbohydrates play various roles, including cell signaling, immune response, and cellular recognition processes.
Unlike prosthetic groups, the carbohydrate components in glycoproteins are not permanently or tightly attached in a way that fulfills a critical function for the protein itself. While these carbohydrate groups can be essential for the protein's role in cellular communication or immune system defense, they don't have the same permanent and integral nature as prosthetic groups like the heme in haemoglobin.
In essence, while glycoproteins are essential for various cellular processes due to their carbohydrate components, these components do not meet the criteria to be considered prosthetic groups. They are more involved in transient and reversible biological interactions.

Nucleoprotein

Nucleoproteins are complexes formed from proteins and nucleic acids, such as DNA or RNA. These complexes are crucial in various biological activities, including the storage and expression of genetic information within the cell.
The key aspect of nucleoproteins is their association with nucleic acids. While these associations are vital for many functions, such as the stabilization of DNA or regulation of gene expression, the nucleic acids are not considered prosthetic groups. The connection between proteins and nucleic acids in nucleoproteins doesn't fulfill the tight and permanent criteria for a prosthetic group.
Furthermore, nucleoproteins like histones in chromatin help package DNA into chromosomes, ensuring proper regulation and accessibility. This functional role emphasizes their importance, but again, this relationship is more about dynamic interaction rather than serving as a permanently integrated prosthetic role.