Thank you for reporting, we will resolve it shortly
Q.
A DNA sample is $13.6 \, nm$ long. It has 10% cytosine molecules calculate the number of weak hydrogen bonds in the given sample.
NTA AbhyasNTA Abhyas 2020Molecular Basis of Inheritance
Solution:
Length of DNA sample $ \, =13.6 \, nm$ . Length of $1 \, turn=3.4 \, nm$ . Thus No. of turns in the sample $=\frac{13.6 n m}{3.4 n m}=4$
No. of nucleotides in 1 turn $= \, 20$ . Thus, No. of nucleotides in the given sample $= \, 20\times 4=80$
Since cytosine is 10%, By Chargaff's rule, $G \, = \, C \, = \, 10\%$ while $A \, = \, T \, = \, 40\%$
No. of Guanine molecules $=\frac{1}{1}x \, 8=8$ . No. of Cytosine $= \, 8$
No. of Adenine $=\frac{40}{100}\times \, 80=32$ . No. of Thymine $= \, 32$
Thus, no. of horizontal steps with GC linkage $= \, 8$ and No. of horizontal steps with AT linkage $= \, 32$
GC are linked by 3 weak hydrogen bonds. Thus no. of weak hydrogen bonds due to GC linkage $= \, 8\times \, 3 \, =24$
AT are linked by 2 weak hydrogen bonds. Thus no. of weak hydrogen bonds due to AT linkage $=32\times 2=64$
Total no. of weak hydrogen bonds in the given sample $= \, 24 \, + \, 64 \, = \, 88$