If a double stranded DNA has 20 per cent of cytosine, calculate the percent of adenine in the DNA.

Answer 1

DNA has four different types of bases that come in complementary pairs.

1) Adenine (A) binds with thymine (T)

2) Cytosine (C) binds with guanine (G)

From 2), if there is 20% C, we know there is also 20% G.

C and G bases together make up 40% of the DNA, leaving 60% to be split between A and T. From 1), we know that % A = % T. Therefore, there is 30% A and 30% T in the DNA.