Which group marks the 5' end of DNA?

Which group marks the 5' end of DNA?

• A. -OH group
• B. Phosphate
• C. Amino group
• D. Methyl group

Answer: (B)

The 5' end is marked by a phosphate group attached to the 5' carbon of the sugar in the DNA backbone. DNA strands are built by linking the 5' phosphate of one nucleotide to the 3' hydroxyl of the previous one, so the terminus at that end carries a phosphate, while the other end ends with a free 3' hydroxyl. This distinction between a terminal phosphate at the 5' end and a free -OH at the 3' end is what defines the directionality of DNA strands. The other groups aren’t used to mark the ends: the -OH marks the 3' end, while amino or methyl groups aren’t involved in defining the termini.

The 5' end is marked by a phosphate group attached to the 5' carbon of the sugar in the DNA backbone. DNA strands are built by linking the 5' phosphate of one nucleotide to the 3' hydroxyl of the previous one, so the terminus at that end carries a phosphate, while the other end ends with a free 3' hydroxyl. This distinction between a terminal phosphate at the 5' end and a free -OH at the 3' end is what defines the directionality of DNA strands. The other groups aren’t used to mark the ends: the -OH marks the 3' end, while amino or methyl groups aren’t involved in defining the termini.