Question

In a double helix of DNA molecule of 10 coils, if there are 30 adenine nitrogen bases, what is the number of guanine, nitrogen bases :

• A. 30
• B. 60
• C. 70
• D. 80

Answer 1

Answer: (C)

Total number of coils in a DNA molecule =10. We know that total number of nitrogen bases are present in a coil =20 (or 10 pairs). Thus, total number of bases in 10 coils $=10\times 20=200$ Acc. to Chargaff Total number of purine = pyrimidine $A+G=C+T$ $\therefore$ out of 200 bases $A+G=100;C+T=100$ A = 30 (given); Thus, $G=100-30=70$