Final answer:
Phosphate groups are linked to the 5' end and ribose or deoxyribose sugars are found at the 3' end in nucleic acid structures, forming a sugar-phosphate backbone with a specific orientation crucial for DNA replication and transcription.
Step-by-step explanation:
Phosphate is attached to the 5' end while ribose (or deoxyribose in DNA) is a part of the structure at the 3' end of a nucleic acid strand. In nucleic acids, the sequence of nucleotide building blocks is joined together by phosphodiester linkages that connect the 3' hydroxyl group of one nucleotide's sugar to the phosphate attached to the 5' carbon of the next nucleotide. This creates a backbone with a repeating pattern of sugar-phosphate-sugar-phosphate, with the bases sticking out away from this backbone.
In a completed DNA or RNA strand, one end will have an exposed phosphate group at the 5' carbon of its terminal sugar, known as the 5' end. The other end will have an exposed hydroxyl group at the 3' carbon of its terminal sugar, referred to as the 3' end. This orientation is significant because DNA synthesis occurs in the 5' to 3' direction and plays a crucial role in processes such as DNA replication and transcription.