Final answer:
The DNA strands running in opposite directions in a double helix, one from 5' to 3' and the other from 3' to 5', is known as having an antiparallel orientation.
Step-by-step explanation:
When two strands of DNA in a double helix run in opposite directions, one being 5' to 3' and the other 3' to 5', this characteristic is called antiparallel orientation. This means the 5' end of one strand faces the 3' end of the other strand, which is crucial for many cellular processes including DNA replication and nucleic acid interactions.
Each strand has a backbone made up of sugar (deoxyribose) and phosphate, and these run like the rails of a spiral stair ladder with the nitrogenous bases adenine, thymine, guanine, and cytosine forming the steps through hydrogen bonds.