A DNA molecule typically consists of two strands. These strands are intertwined to form the iconic double helix structure.
Understanding the Double Helix
The two strands are held together by hydrogen bonds between complementary base pairs: adenine (A) with thymine (T), and guanine (G) with cytosine (C). Each strand runs in an opposite direction to the other (antiparallel). This specific pairing and arrangement are crucial for DNA's function in storing and transmitting genetic information.
- Example: Imagine a twisted ladder; the sides represent the sugar-phosphate backbones of each strand, and the rungs are the base pairs connecting them.
Several sources support this:
- The provided text states: "The two strands of DNA in a double helix are held together by pairing between the nitrogenous bases..."
- Genome.gov describes DNA as "made of two linked strands that wind around each other".
- Wikipedia confirms the "two strands of DNA run in opposite directions to each other".
- Vanderbilt University research guide indicates that "Each chromosome consists of a single two-stranded DNA molecule".
Important Note on Chromosome Number and DNA Strands
While a single DNA molecule has two strands, it's important to distinguish this from the total number of DNA strands within a cell. Human cells, for example, contain 46 chromosomes. Since each chromosome is composed of a single, double-stranded DNA molecule, human somatic cells have 92 total strands of DNA. This distinction is crucial for clarity.
However, it's also worth noting that while a double helix is the most common structure, other DNA structures like quadruplex DNA have been discovered. These are rare and less common.
