Where is a free phosphate group typically attached in a nucleotide?

In a nucleotide, a free phosphate group is primarily attached to the 5' end carbon of the sugar molecule. This arrangement is crucial for the structural formation of nucleic acids like DNA and RNA. The attachment occurs specifically through a phosphoester bond between the phosphate group and the hydroxyl group on the 5' carbon of the sugar.

This positioning allows nucleotides to link together via their phosphate groups to form a phosphodiester bond, creating the backbone of nucleic acid strands. The 3' end carbon of the sugar typically has a hydroxyl (-OH) group that can participate in bonding with the next nucleotide, highlighting the directional nature of DNA and RNA. Thus, the 5' phosphate group is integral to cell processes such as replication and transcription, emphasizing the role of nucleotides in genetic information transfer.