The two ends of a strand of DNA are called the
A. starting end and the ending end, based on the orientation of the DNA within the chromosome.
B. 5′ and the 3′ end, based on modifications in the deoxyribose sugar.
C. sense end and the antisense end, based on the location of the phosphate groups.
D. codon and the anticodon, based on the order of the deoxyribose sugars and the phosphate groups.

DNA is a large molecule which acts as genetic material of the organisms. DNA exists in intertwined double helical form consisting of two DNA chains or strands.

Each DNA strand is a long, continuous thread like structure made up of repeating units called nucleotides. Each nucleotide comprises of three subunits: five carbon sugar called deoxyribose, phosphate group and nitrogen-containing bases.

Each nucleotide is connected to next nucleotide by the formation of phopho-diester bond between free 5’ phosphate (PO³⁻₄ ) group of one nucleotide and the 3’-OH group of another deoxy-ribose sugar. This gives a phosphate-sugar-phosphate-sugar chain which forms the backbone of DNA molecule and is read in 5’ -> 3’ direction.

Thus, option B is the correct answer.