Problem 116 - Arihant Objective Approach to Organic Chemistry for IIT JEE and NEET all Medical Entrances Part 4

Question

The base present in \(\mathrm{DNA}_{;}\)but not in RNA is : (a) guanine (b) adenine (c) uracil (d) thymine

Step-by-Step Solution

Answer

Thymine is the nitrogenous base present in DNA but not in RNA.

Step 1: Understanding the Question

The question asks us to identify a nitrogenous base that is present in DNA but not in RNA. In other words, we need to recall the specific bases that make up DNA and RNA.

Step 2: Identifying DNA Bases

DNA consists of four nitrogenous bases: adenine (A), thymine (T), cytosine (C), and guanine (G). These are the building blocks of DNA's double helix structure.

Step 3: Identifying RNA Bases

RNA also has four bases, but they are slightly different: adenine (A), uracil (U), cytosine (C), and guanine (G). Notice how uracil replaces thymine in RNA.

Step 4: Comparing the Bases

By comparing the bases found in DNA and RNA, we see that thymine is unique to DNA while uracil is unique to RNA. The other bases, adenine, cytosine, and guanine, are found in both DNA and RNA.

Step 5: Answering the Question

The base present in DNA but not in RNA is thymine, as it is replaced by uracil in RNA.

Key Concepts

Nitrogenous Bases

Nitrogenous bases are essential components of nucleotides, which are the building blocks of genetic material in living organisms. These bases come in a few varieties and play a crucial role in storing genetic information.
In both DNA and RNA, nitrogenous bases are categorized into two types:

• Pyrimidines: These are single-ring structures. In DNA, they include thymine (T) and cytosine (C), while in RNA, thymine is replaced by uracil (U), with cytosine remaining the same.
• Purines: These are double-ring structures and include adenine (A) and guanine (G) in both DNA and RNA.

These bases pair with each other through hydrogen bonds, forming the steps of the DNA double helix ladder or coding regions in RNA. In DNA, adenine pairs with thymine, and cytosine pairs with guanine, while in RNA, adenine pairs with uracil. Understanding these bases is crucial for comprehending how genetic information is encoded and transmitted.

Difference between DNA and RNA

DNA (Deoxyribonucleic acid) and RNA (Ribonucleic acid) are both nucleic acids present in cells, but they have distinct differences in their structures and functions.
Firstly, their sugar components differ. DNA contains deoxyribose sugar, which lacks one oxygen atom compared to the ribose sugar in RNA. This small difference affects the overall stability and functionality of these molecules.
Another key difference is in their nitrogenous bases. DNA uses adenine (A), thymine (T), cytosine (C), and guanine (G), whereas RNA uses uracil (U) in place of thymine, along with the other three bases (A, C, G).
Moreover, DNA is typically double-stranded, forming a stable double helix structure, while RNA is usually single-stranded, allowing it more versatility in function. DNA serves as the long-term storage of genetic information, whereas RNA plays a more immediate role, including acting as a messenger (mRNA), participating in protein synthesis (tRNA and rRNA), and regulating gene expression. Comprehending these differences is vital for understanding how genetic material functions in biological processes.

Genetic Material

Genetic material refers to the molecules responsible for inheritance and the storage of genetic information in organisms. The primary genetic material in cellular life forms is composed of DNA and, to some extent, RNA.
DNA is the main carrier of genetic information in most organisms, stored in the chromosomes within a cell's nucleus or in plasmids for prokaryotes. This genetic information dictates everything about an organism's form, functions, and traits. It's like a biological instruction manual.
RNA, on the other hand, plays a multifaceted role when it comes to genetic material. Not only does it help decode the genetic instructions from DNA into functional proteins through mRNA, tRNA, and rRNA, but some viruses, like retroviruses, store their genetic information in RNA instead of DNA.
The knowledge of how genetic material operates is fundamental to fields such as genetics, biotechnology, and medicine, influencing how we understand development, disease, and inheritance.