Final answer:
DNA is composed of two strands arranged antiparallel to each other, with the 5' end of one strand opposite the 3' end of the other, forming a double helix where the phosphate backbones are on the outside and the bases are on the inside, specifically pairing adenine with thymine and guanine with cytosine.
Step-by-step explanation:
The concept of antiparallel strands in DNA refers to the orientation of the two complementary strands of the double helix. In a DNA molecule, the two strands are arranged next to each other, such that the 5' to 3' direction of one strand is opposite to the 3' to 5' direction of the other strand. This antiparallel arrangement is crucial for the function and replication of DNA.
The phosphate backbones of DNA are on the outside of the molecule, while the nitrogenous bases are on the inside, forming hydrogen bonds with complementary bases across the two strands. These bases pair specifically: adenine with thymine and guanine with cytosine. The antiparallel nature allows for the bases to be aligned so that hydrogen bonding can occur between them.
This structure was elucidated by James Watson and Francis Crick in 1953, with contributions from scientists such as Rosalind Franklin. The antiparallel strands twist to form the iconic double helix structure, resembling a spiral staircase, with the complementary bases forming the steps, or rungs, of the staircase.