Final answer:
The description "anti-parallel" refers to the arrangement of the two strands in the DNA double helix, where they run in opposite directions, with one strand oriented 5' to 3' and the other 3' to 5'. This anti-parallel orientation is crucial for DNA replication and transcription, ensuring proper base pairing and stable DNA structure.
Step-by-step explanation:
The term "anti-parallel" describes the orientation of the two strands that make up the double helix structure of DNA. Within this structure, the strands run in opposite directions, meaning one strand runs from the 5' to the 3' end, while the complementary strand runs from the 3' to the 5' end. This orientation is critical for many DNA processes, such as replication and transcription, because it allows the enzyme machinery of the cell to interact with DNA in a consistent direction.
Each strand has a backbone made of alternating sugar (deoxyribose) and phosphate groups, with the nitrogenous bases (adenine, thymine, cytosine, and guanine) attached to the sugar. These bases form hydrogen bonds with their complementary bases on the opposite strand—adenine pairs with thymine and cytosine pairs with guanine. The anti-parallel nature of the two strands enables the bases to align perfectly for the formation of these hydrogen bonds, giving the DNA its stability and specificity.
Through the efforts of James D. Watson and Francis Crick, and based on the research of Rosalind Franklin and others, it was concluded that DNA is composed of two nucleic acid chains running anti-parallel to each other, twisted into a double helix. This discovery was pivotal in understanding how genetic information is stored, replicated, and expressed within living organisms.