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Q.
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 :
EAMCETEAMCET 2003
Solution:
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 $