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

(b) haemoglobin

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. These can include metal ions, vitamins, or organic compounds.

Step 2: Identifying Prosthetic Groups

Look for the mentioned proteins and determine if they have any non-protein unit tightly bound: 1. Glycoprotein - contains carbohydrate groups attached to the polypeptide chain, not typically classified as a prosthetic group. 2. Haemoglobin - contains the heme group, which is tightly bound and essential for its function to carry oxygen. 3. Nucleoprotein - contains nucleic acids bound to proteins, sometimes contains tightly bound non-polypeptide elements.

Step 3: Analyzing Options

Based on the definitions: - Haemoglobin contains the heme prosthetic group. - Glycoprotein and nucleoprotein can contain carbohydrate or nucleic acid components which are essential but not as tightly bound or universally recognized as classical prosthetic groups.

Step 4: Conclusion

Out of the options given, haemoglobin (choice b) is known to contain a recognized prosthetic group (heme) required for its function. Thus, haemoglobin is the correct choice.

Key Concepts

Glycoprotein

Glycoproteins are fascinating molecules that play essential roles in many biological processes. They are proteins that have carbohydrate groups attached to the polypeptide chain. These carbohydrate groups can include sugars like glucose, mannose, and galactose.
Glycoproteins serve various important functions:

• They are crucial in cell-cell recognition, which is vital for immune response.
• They help in stabilizing protein structures, ensuring they fold correctly and function well.
• They can play roles in signaling pathways, acting as receptors on cell surfaces.

Though these carbohydrate groups are integral to the protein's function, unlike a prosthetic group, they are not tightly or permanently attached. Instead, they are attached through glycosidic bonds which can be broken under certain conditions. Therefore, while glycoproteins are essential, their carbohydrate components are not typically classified as prosthetic groups.

Haemoglobin

Haemoglobin is a critical protein found in red blood cells responsible for transporting oxygen throughout the body. This protein's ability to bind oxygen is due to its prosthetic group, called heme. The heme group contains an iron ion core that can bind to oxygen, enabling haemoglobin to play its vital role in respiration.
Here are some interesting aspects of haemoglobin's structure and function:

• The heme group is a complex organic structure with an iron atom at its center, indispensable for oxygen binding.
• Haemoglobin consists of four polypeptide chains, each containing a heme group, allowing it to bind up to four oxygen molecules.
• It not only carries oxygen from the lungs to tissues but also helps carry carbon dioxide back to the lungs for exhalation.

The unique feature of haemoglobin is that its heme group is permanently attached, a classic example of a prosthetic group. This attachment is essential for the protein's functionality, showcasing why haemoglobin is the textbook case of a protein with a prosthetic group.

Nucleoprotein

Nucleoproteins are an intriguing group of complexes formed when nucleic acids, such as DNA or RNA, are bound to proteins. This binding is crucial for many cellular functions, including the organization of genetic material and the regulation of gene expression.
Key roles and characteristics of nucleoproteins include:

• They participate in the packaging of DNA in structures called chromatin, aiding in the efficient storage and regulation of genetic information.
• Nucleoproteins are involved in various cellular processes such as DNA replication and repair.
• They can form part of ribonucleoprotein complexes involved in protein synthesis and RNA processing.

While nucleoproteins do involve non-protein components, like nucleic acids, these are not tightly bound in the way prosthetic groups, like heme, are. Therefore, while essential, these components do not fit the classical definition of a prosthetic group as heme does in haemoglobin. Instead, nucleoproteins illustrate the complexity of interactions that cells use to control and execute their various functions.