Problem 132 - Arihant Objective Approach to Organic Chemistry for IIT JEE and NEET all Medical Entrances Part 4

Question

The purine base present in RNA is: (a) guanine (b) thymine (c) cytosine (d) uracil

Step-by-Step Solution

Answer

The purine base present in RNA is (a) guanine.

Step 1: Understand the Question

The question asks us to identify which purine base is present in RNA from the given options. RNA is one of the nucleic acids found in cells, and it is important to know its base composition.

Step 2: Recall the Bases in RNA

RNA is composed of four nitrogenous bases: adenine, uracil, guanine, and cytosine. Among these, we need to determine which bases are purines. Remember, RNA does not contain thymine.

Step 3: Differentiate Between Purines and Pyrimidines

There are two types of bases in nucleic acids: purines and pyrimidines. Purines include adenine and guanine, while pyrimidines include cytosine and uracil in the context of RNA.

Step 4: Identify the Correct Purine Base

From Step 2 and Step 3, we know that the purine bases are adenine and guanine. Among the given options, only guanine is a purine. Therefore, guanine is the purine base present in RNA.

Key Concepts

Nucleic Acids

Nucleic acids are essential biomolecules in every living cell that play a vital role in storing and transmitting genetic information. There are two main types of nucleic acids: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). Each type has a different function but shares a similar structural framework.

Nucleic acids are composed of long chains of monomers known as nucleotides. Each nucleotide consists of three components:

• A phosphate group
• A five-carbon sugar (deoxyribose in DNA and ribose in RNA)
• A nitrogenous base

These components work together to form the backbone of nucleic acids and facilitate the encoding of genetic information. RNA, in particular, is often single-stranded and plays a crucial role in translating genetic information into proteins. Understanding these structures and functions helps us appreciate how genetic traits are inherited and expressed.

Nitrogenous Bases

Nitrogenous bases are a class of organic molecules that are essential components of nucleotides in nucleic acids. These bases come in five primary forms: adenine, guanine, cytosine, thymine, and uracil. In the context of DNA and RNA, these bases pair in specific ways, known as base pairing rules, to form the rungs of the nucleic acid structure.

In RNA, the nitrogenous bases are adenine (A), uracil (U), guanine (G), and cytosine (C). Uracil replaces thymine, which is found in DNA. The bases pair in a way that ensures the proper transmission of genetic information:

• Adenine pairs with uracil in RNA
• Guanine pairs with cytosine in both RNA and DNA

These base pairings are essential for the accurate decoding of genetic instructions during processes like transcription and translation.

Purines and Pyrimidines

Purines and pyrimidines are the two categories of nitrogenous bases found in nucleic acids. These categories are distinguished by their ring structures, which have implications for their roles in nucleotide pairing and overall nucleic acid structure.

Purines are characterized by a two-ring structure and include:

• Adenine (A)
• Guanine (G)

Pyrimidines, on the other hand, have a single-ring structure and include:

• Cytosine (C)
• Uracil (U) in RNA, and thymine (T) in DNA

In RNA, the purine bases are adenine and guanine. Guanine is the purine base listed in the original exercise options, making it the correct answer. Understanding the structural differences helps in recognizing how these bases pair to form the stable double helical structure of DNA and the functional structures of RNA.