Equal Length Of A–T and C–G Pairs Means A Ladder With Perfectly Uniform Rungs
- The stability of the DNA double helix depends on the fact that base pairs always consist of one purine and one pyrimidine.
- These rungs are formed by adenine-thymine (A-T) and cytosine-guanine (C-G) pairs.
These rungs are formed by adenine-thymine (A-T) and cytosine-guanine (C-G) pairs.
Why Do A-T and C-G Pairs Have Equal Length?
- Base pairing in DNA always links one purine with one pyrimidine:
- Adenine (A) and guanine (G) are purines, which have a double-ring structure.
- Thymine (T) and cytosine (C) are pyrimidines, which have a single-ring structure.
- If two purines paired together, the rung would be too wide.If two pyrimidines paired, the rung would be too narrow.
- However, pairing one purine with one pyrimidine ensures a constant width of the DNA helix.
- Despite A–T pairs having two hydrogen bonds and C–G pairs having three hydrogen bonds, the distance between the two strands remains consistent because the pairing geometry compensates for this difference.
