Question

the figure below is an illustration of a double - stranded dna molecule. the 3’ end of the strand on the left is labeled. which nucleotide was the last nucleotide added during synthesis of the lefthand strand?

Explanation:

Step1: Recall DNA synthesis direction

DNA synthesis occurs in the 5' to 3' direction. The 3' - end of the left - hand strand is labeled. So the last nucleotide added is at the 5' - end of the left - hand strand.

Step2: Identify the 5' - end nucleotide

Looking at the left - hand strand, the nucleotide at the opposite end of the labeled 3' - end (i.e., the 5' - end) is the one at the top. In the figure, the top - most nucleotide on the left - hand strand is 'a'.

Answer:

a