Calculate the number of hydrogen bonds in DNA molecule having 500 deoxyribose sugar. Assume that 30% of nitrogenous bases is cytosine.

No. of nitrogenous bases= No. of deoxyribose sugar.
No. of cytosine= 500*0.3
                        = 150
No. of cytosine= No. of guanine= 150
Total G+C= 300
Total A+T= 500-300=200
No. of A= No. of T= 200/ 2= 100
Between A and T there is the presence of 2 hydrogen bonds and between G and C there is the presence of 3 hydrogen bonds.
Therefore, total number of hydrogen bond in the DNA = (100*2)+( 150*3)= 200+450= 650.