Question

The base sequence on one of the strands of DNA is TAC TAG GAT.

1. Give the base sequence of its complementary strand.
2. What is the distance maintained between the two consecutive paired bases in the DNA molecule?
3. Who contributed the base complementarity rule?
4. Categorise these bases using their full names.
5. What holds these base pairs together?

Answer 1

1. The base sequence of the complementary DNA strand is ATG ATC CTA.
2. The distance maintained between two consecutive base pairs in a DNA molecule is 0.34 nm (or 3.4 Å).
3. Erwin Chargaff contributed the base complementarity rule (often called Chargaff’s Rules), which states that in a DNA molecule, the amount of Adenine equals Thymine and the amount of Guanine equals Cytosine.
4. The nitrogenous bases are categorised into two groups:
   • Purines: Adenine and Guanine.
   • Pyrimidines: Thymine and Cytosine.
5. The base pairs are held together by Hydrogen bonds. Specifically, there are two hydrogen bonds between Adenine and Thymine (A = T) and three hydrogen bonds between Guanine and Cytosine (G ≡ C).