Final answer:
The 5′ end of a nucleic acid refers to the phosphate group found at the 5′ carbon of the first nucleotide, anchoring the start of the nucleic acid chain.
Step-by-step explanation:
The 5′ end of a nucleic acid molecule refers to the phosphate group on the 5′ carbon of the first nucleotide. In the structure of nucleic acids, nucleotides are linked together through a series of covalent bonds known as phosphodiester bonds between the phosphate group of one nucleotide and the hydroxyl group on the 3′ carbon of the adjacent nucleotide. This structure gives nucleic acids their sense of directionality, with a free phosphate group at the 5′ end and a free hydroxyl group at the 3′ end.