Final answer:
Option 1.
Anti-parallel describes the orientation of the two DNA strands that run in opposite directions, which is fundamental for DNA's structure and function.
Step-by-step explanation:
The term anti-parallel in reference to the DNA double helix means that the two strands of DNA run in opposite directions. Specifically, one strand runs from the 5' to the 3' direction, and the other strand runs from 3' to 5' direction. This orientation is crucial for various DNA functions, like replication and nucleic acid interactions. In this anti-parallel configuration, the sugar and phosphate components form the backbone of the DNA structure, and the nitrogenous bases (adenine, thymine, cytosine, and guanine) are in the interior, forming base pairs connected by hydrogen bonds.
Therefore, the correct option is: The two strands of DNA run in opposite directions.