Problem 33 - Objective Biology for NEET

Question

Select the incorrect matching regarding the following diagram: (a) Purine Its metabolism forms uric acid (b) Uracil \(-\) It is exclusively found in RNA only (c) Adenylic acid \(-\) Monomer of both RNA and DNA (d) Cholesterol \(-\) Forms a part of cell membrane

Step-by-Step Solution

Answer

All the matchings are correct.

Step 1: Purine

The first statement is correct. Purine metabolism indeed forms uric acid. Therefore, (a) is not the incorrect matching.

Step 2: Uracil

The second statement is also correct. Uracil is only found in RNA, replacing Thymine which is found in DNA. Therefore, (b) is not the incorrect matching.

Step 3: Adenylic Acid

The third statement is correct. Adenylic Acid, also known as Adenine, is a base part of the genetic material and can be a part of DNA as well as RNA. Therefore, (c) is not the incorrect matching.

Step 4: Cholesterol

The fourth statement is correct. Cholesterol is a lipid that forms part of the cell membrane and is important for cell fluidity and integrity. Therefore, (d) is not the incorrect matching.

Key Concepts

Purine metabolism

Purine metabolism is a crucial biological process where purine bases are synthesized and broken down. This process is vital for producing nucleotides, which are the building blocks of DNA and RNA. Purines, such as adenine and guanine, are metabolized to yield uric acid. This is the final breakdown product in humans. Understanding purine metabolism is essential for diagnosing certain medical conditions, like gout, where excess uric acid accumulates in the body.
Purine metabolism involves several steps including:

• Synthesis: The body creates purines from simpler molecules; this is called de novo synthesis.
• Salvage: The body reuses purines obtained from the breakdown of nucleotides.
• Degradation: Purines are broken down into uric acid, which is excreted in urine.

Managing purine intake and metabolism is crucial for maintaining optimal health.

Uracil in RNA

Uracil is one of the four nucleobases in the nucleic acid of RNA. It is unique to RNA and replaces thymine, which is found in DNA. Uracil pairs with adenine in RNA, helping to form the structure of the RNA molecule.
The role of uracil in RNA includes:

• Forming hydrogen bonds with adenine to help stabilize the RNA structure.
• Participating in coding, decoding, regulation, and expression of genes.
• Being a part of various forms of RNA, such as mRNA, tRNA, and rRNA.

Uracil's presence makes RNA less stable than DNA, which fits its role as a temporary carrier of genetic information.

Adenylic acid

Adenylic acid, also known as adenosine monophosphate (AMP), is a nucleotide found in RNA and DNA. It consists of an adenine base attached to a ribose sugar and a single phosphate group. In the cell, AMP plays several roles:

• As a part of RNA, it helps in protein synthesis and other cellular processes.
• In DNA, it contributes to the formation of the DNA double helix.
• Regulation of energy through its relation to ATP and ADP; AMP can be converted to form ATP, the energy currency of the cell.

Understanding adenylic acid is important for grasping how energy is managed and genetic information is stored and expressed.

Cholesterol in cell membrane

Cholesterol is a type of lipid found within the cell membrane. It plays a crucial role in maintaining the membrane's structure and function. Cholesterol molecules fit between phospholipid molecules in the cell membrane, providing stability and flexibility.
The role of cholesterol in the cell membrane includes:

• Modulating membrane fluidity, making it less permeable to very small water-soluble molecules that might otherwise pass freely through.
• Participating in cell signaling, impacting how cells communicate and adapt to changes in their environment.
• Assisting in the creation of lipid rafts, which are involved in various cellular processes, including trafficking of proteins and cell communication.

Without adequate cholesterol, cells could become too rigid or too fluid, impeding their function and communication.