Final answer:
The term "antiparallel structure" in DNA refers to the orientation of the two strands, with the 5' end of one strand facing the 3' end of the other. This is essential for DNA replication and the correct pairing of nitrogenous bases.
Step-by-step explanation:
When we say that DNA has an "antiparallel structure," we are referring to the orientation of the two strands that make up the DNA molecule. In the double-helix structure of DNA, one strand runs in the 5' to 3' direction, while the other strand runs in the 3' to 5' direction. This means that the 5' end of one strand faces the 3' end of the other strand, creating an antiparallel arrangement. This antiparallel nature is crucial for DNA replication and various nucleic acid interactions.
This configuration allows the nitrogenous bases adenine, thymine, cytosine, and guanine to pair up across the strands, with adenine always pairing with thymine and cytosine always with guanine. These complementary base pairs are connected by hydrogen bonds, and they stack in the interior of the helix like the steps of a staircase, contributing to the structural stability of DNA.
The antiparallel structure is a key feature of DNA and helps to ensure that when DNA replicates, each new double helix contains one old strand and one new strand, a process known as semiconservative replication.