Problem 144 - A Complete Resource Book in Chemistry for JEE Main

Question

Match the following: List I List II 1\. Nucleic acid A D.N.A. 2\. Uracil B Hormones 3\. Thymine C Polynucleotides 4\. Double helix structure D R.N.A The correct matching is 1 2 3 (a) C \(\mathrm{D}\) \(\mathrm{A}\) A (b) C \(\mathrm{A}\) \(\mathrm{A}\) D (c) C \(\mathrm{D}\) B \(\mathrm{A}\) (d) \(\mathrm{C}\) B D \(\mathrm{C}\)

Step-by-Step Solution

Answer

The correct matching is (a) C D A A.

Step 1: Understanding the Problem

We have two lists where we need to match items from List I to List II. List I contains biological components, and List II contains their descriptions or related structures.

Step 2: Analyzing List I and List II

List I: 1. Nucleic acid, 2. Uracil, 3. Thymine, 4. Double helix structure. List II: A. DNA, B. Hormones, C. Polynucleotides, D. RNA.

Step 3: Matching Nucleic Acid with List II

Nucleic acids are composed of polymers of nucleotides. The correct match for Nucleic acid is option C (Polynucleotides) since DNA and RNA are both nucleic acids made up of these structures.

Step 4: Matching Uracil with List II

Uracil is a nitrogenous base found in RNA but not in DNA. Thus, it matches with D (RNA).

Step 5: Matching Thymine with List II

Thymine is a nitrogenous base that is found in DNA. Therefore, it matches with A (DNA).

Step 6: Matching Double Helix Structure with List II

The double helix structure is a description of DNA. Therefore, it matches with A (DNA).

Step 7: Choosing the Correct Match

The correct sequence is: 1. C, 2. D, 3. A, 4. A. Hence, the correct option is (a) C D A A.

Key Concepts

DNA

DNA, short for deoxyribonucleic acid, is one of the most vital macromolecules for life as it contains the genetic instructions that are essential for the development and function of living organisms. It stores the information needed for an organism's growth and reproduction.
DNA molecules consist of two long strands that coil around each other to form a double helix.

• It's made up of building blocks called nucleotides.
• Each nucleotide includes a sugar group, a phosphate group, and one of four types of nitrogenous bases.

These nitrogenous bases are adenine (A), thymine (T), cytosine (C), and guanine (G) that pair specifically—A with T and C with G—through hydrogen bonds across the two strands.
This specific pairing is crucial for DNA's purpose in the accurate copying of genetic information during cell division.

RNA

RNA, or ribonucleic acid, plays a crucial role in converting the genetic information contained within DNA into proteins essential for cellular function. Unlike DNA, RNA is usually single-stranded, which makes it more versatile in function.
RNA is responsible for several key biological processes:

• Messenger RNA (mRNA): Carries genetic information from DNA to ribosomes for protein synthesis.
• Transfer RNA (tRNA): Brings amino acids to ribosomes to aid in protein assembly.
• Ribosomal RNA (rRNA): Combines with proteins to form ribosomes which catalyze the assembly of amino acids into protein chains.

Importantly, RNA contains the nitrogenous base uracil (U) instead of thymine, which is found in DNA. This small difference significantly affects RNA's structure and function.

Nitrogenous bases

Nitrogenous bases are organic molecules that serve as the fundamental units of the genetic code in both DNA and RNA. They are responsible for the storage and transfer of genetic information.
The bases are categorized into two groups:

• Pyrimidines: Include cytosine (C), thymine (T), and uracil (U). Thymine is unique to DNA, while uracil is only found in RNA.
• Purines: Include adenine (A) and guanine (G), which are found in both DNA and RNA.

These nitrogenous bases form base pairs through hydrogen bonding, essential for translating genetic information into amino acids and then into proteins. The specific pairing (A with T/U and C with G) is vital for the stability and replication of nucleic acids.

Double helix structure

The double helix is the iconic structure of DNA, first described by James Watson and Francis Crick in 1953. This spiral form resembles a twisted ladder, where the sugar-phosphate components form the "rails," and paired nitrogenous bases form the "rungs."
Key features of the double helix include:

• Antiparallel orientation: The two DNA strands run in opposite directions, which is essential for replication and function.
• Complementary base pairing: Adenine pairs with thymine, and cytosine pairs with guanine, ensuring accurate replication of genetic material.

This structure not only facilitates DNA replication but also ensures its stability and protection from damage. It elegantly illustrates the precision needed for genetic information to be reliably copied and passed on to succeeding generations.