Answer:
1. A
2. C
3. B
Explanation:
1. The DNA here has a Guanine(G) content of 15% and as G is equal to C,
[tex]$GC=G+C$[/tex]
= 15% + 15%
= 30%
As the GC content is less than 50 % , so the DNA is not a GC rich DNA. Therefore, for a DNA to be GC rich in content, G+C should be more than 50%.
Therefore the correct option is (A), The strand has a GC content of 30%.
2. With a content of 15% Guanine, we calculate the proportions of the four bases. They are :
[tex]$A+T=G+C$[/tex] and [tex]$A=T, G=C$[/tex]
∴ [tex]$A+T=15\% +15\%$[/tex]
[tex]$=30\%$[/tex]
So when we substract 30% from 100% , we get 70%. Now this 70% is then distributed in the equal proportions for [tex]$A$[/tex] and [tex]$T$[/tex].
Therefore, we have:
[tex]$A=30\%, T=35\%, G=15\%$[/tex] and [tex]$C=15\%$[/tex]
Therefore we calculate the content of purines [tex]$(A,G)$[/tex] and pyrimidines [tex]$(C,T)$[/tex].
Purine content : [tex]$A+G = 35\% + 15\%$[/tex]
[tex]$=50\%$[/tex]
Pyrimidine content : [tex]$C+T=15\%+35\%$[/tex]
[tex]$=50\%$[/tex]
Therefore, the correct option is (C).
3. Yes, the GC rich strand of the DNA is more stable the a GC low content DNA. But this stability is not due to the hydrogen bonds, it is mainly due to the stacking interaction known as base stacking.
So the correct option is (B).