Question

1: Four given molecules of nucleic acids have the following composition of nitrogenous bases:

Molecule 1: 30% A, 20% G, 30% T, 20% C, 0% U

Molecule 2: 20% A, 30% G, 0% T, 30% C, 20% U

Molecule 3: 20% A, 50% G, 10 % T, 20% C, 0%U

Molecule 4: 10% A, 60% G, 0% T, 15% C, 15% U

Which type of nucleic acids are these - DNA or RNA? Also describe if they are single stranded or double stranded?

Answer 1

Molecule 1: 30% A, 20% G, 30% T, 20%C, 0% U- This is a double stranded DNA molecule. Because it has A, T, G and C with ratio of 1 for A:T and G:C (according to Chargaff rule).

Molecule 2: 20% A, 30% G, 0% T, 30% C, 20% U- This is a double stranded RNA molecule. Because it has A, U, G and C with ratio of 1 for A:U and G:C.

Molecule 3: 20% A, 50% G, 10% T, 20% C, 0% U- This is a single stranded DNA molecule. Because it has A, T, G and C and it is not following the Chargaff rule of ratio 1 for A:T and G:C.

Molecule 4: 10% A, 60% G, 0% T, 15% C, 15% U- This is a single stranded RNA molecule. Because it has A, U, G and C and it is also not following the Chargaff rule ratio 1 for A:U and G:C.