Question

Which end of a polynucleotide chain contains a free phosphate group?

Options

• The 3′ end

• The 5′ end

• Neither end has a free phosphate group

• Both the 5′ and 3′ ends

Answer 1

The 5′ end of a polynucleotide chain has a free phosphate group attached to the 5′ carbon of the terminal sugar molecule. This is the starting end of the chain. The 3′ end has a free hydroxyl (–OH) group attached to the 3′ carbon of the terminal sugar.