Question

Which carbon atom of ribose sugar is joined to nitrogen base to form nucleoside?

• A. C $-$ 2'
• B. C $-$ 5'
• C. C $-$ 3'
• D. C $-$ 1'

Hint:

To easily remember nucleoside/nucleotide structure, use the "1-3-5" rule for the sugar attachments:
The Base is always at position 1', the next nucleotide connects at position 3', and the Phosphate group is at position 5'.

Answer 1

The Correct Option is D

Step 1: What is a nucleoside?
A nucleoside is just a sugar joined to a nitrogen base. We want the carbon of the sugar that holds the base.

Step 2: Number the sugar carbons.
In ribose the carbons are marked with a dash, like 1', 2', 3', and so on. This keeps them separate from the numbers used on the base.

Step 3: Find the joining carbon.
The base always sits on the first carbon, C-1'. This is the carbon that was part of the open chain carbonyl group.
\[ \boxed{\text{C-1'}} \]