Question:

In nucleoside, the base is attached to which position of the sugar molecule?

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In nucleosides, the base is always attached to the C-1 position of the sugar. This is key in distinguishing nucleosides from nucleotides.
Updated On: May 21, 2025
  • C-1
  • C-2
  • C-3
  • C-5
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The Correct Option is A

Approach Solution - 1

In nucleosides, the nitrogenous base is attached to the C-1 position of the sugar molecule (which is typically a pentose sugar such as ribose or deoxyribose). The C-1 carbon of the sugar connects to the base through a glycosidic bond. Thus, the correct answer is (1) C-1.
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Approach Solution -2

Step 1: Understanding Nucleosides
Nucleosides are molecules formed by the attachment of a nitrogenous base to a sugar molecule. Unlike nucleotides, nucleosides do not have phosphate groups attached. The sugar in nucleosides is either ribose (in RNA) or deoxyribose (in DNA).

Step 2: Structure of the Sugar Molecule
The sugar in nucleosides is a five-carbon sugar called a pentose. The carbons in the sugar are numbered from 1’ to 5’. The 1’ carbon is the carbon to which the base attaches, while the 5’ carbon is where the phosphate group would attach in nucleotides.

Step 3: Attachment of the Base
The nitrogenous base is attached specifically to the 1’ carbon of the sugar via a glycosidic bond. This bond connects the N-9 atom of purines (adenine, guanine) or the N-1 atom of pyrimidines (cytosine, thymine, uracil) to the 1’ carbon of the sugar.

Step 4: Conclusion
Therefore, in a nucleoside, the base is attached to the C-1 position of the sugar molecule, forming the characteristic structure essential for nucleic acid formation.
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