Final answer:
The backbone of the polynucleotide strand consists of alternating sugars and phosphate groups.
Step-by-step explanation:
Nucleic acids such as DNA and RNA consist of long chains of nucleotides that have a sugar-phosphate backbone with nitrogenous bases attached to the sugar. In the structure of DNA, a double helix is formed where two polynucleotide strands are held together by hydrogen bonds between complementary nitrogenous bases with adenine pairing with thymine and guanine pairing with cytosine.
The structure is stabilized by these bonds, forming a unique pattern in which the sugar-phosphate components create the outer framework of the DNA strand, while the pairs of nitrogenous bases (A-T and G-C) are oriented inside, much like the steps of a staircase. These strands run in opposite directions, an arrangement known as antiparallel, with one strand running from the 5' to the 3' direction and the other from 3' to 5'.
This polarity is critical for the function of DNA during processes such as replication and transcription.