Question 13 of 25beginner🧠 RememberShort Answer2 marks

Group the following as nitrogenous bases and nucleosides: Adenine, Cytidine, Thymine, Guanosine, Uracil and Cytosine.

Correct Answer

Nitrogenous bases: Adenine, Thymine, Uracil, Cytosine

Nucleosides: Cytidine, Guanosine

A nitrogenous base is a fundamental component of nucleic acids. There are two types – Purines (Adenine and Guanine) and Pyrimidines (Cytosine, Uracil and Thymine). Adenine, Thymine, Uracil and Cytosine are all nitrogenous bases.

A nucleoside is formed when a nitrogenous base is linked to the OH of 1°C pentose sugar through a N-glycosidic linkage. Examples include adenosine, guanosine, cytidine and uridine. Thus, Cytidine and Guanosine are nucleosides – they consist of a base attached to a sugar without any phosphate group.

Exercise: EXERCISES | Q: 1 | (Page 31)
For More Understanding

Explanation

The question tests the student's understanding of the difference between nitrogenous bases and nucleosides. According to the NCERT context, nitrogenous bases are of two types - Purines (Adenine and Guanine) and Pyrimidines (Cytosine, Uracil and Thymine). A nucleoside is formed when a nitrogenous base links to pentose sugar through N-glycosidic linkage (e.g., adenosine, guanosine, cytidine, uridine). The '-osine' or '-idine' suffix indicates a nucleoside, while '-ine' suffix typically indicates a nitrogenous base.

Solution Steps

  1. Step 1: Identify that nitrogenous bases include Purines (Adenine, Guanine) and Pyrimidines (Cytosine, Uracil, Thymine)

  2. Step 2: Recognize that nucleosides are formed by base + sugar linkage (names end with -osine or -idine)

  3. Step 3: Group Adenine, Thymine, Uracil, Cytosine as nitrogenous bases and Cytidine, Guanosine as nucleosides

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