This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: JIPMER 2018, Subject name: Biochemistry
Melting temperature of DNA is:- 
Select and explain. 
A. Propoional to AT pairs, B. Propoional to GC pairs, C. No relation with base pair composition, D. Directly propoional to length of DNA
B: Propoional to GC pairs
Answer: B: Propoional to GC pairs 
Explanation: Denaturation or melting of two DNA strands means the separation of the two strands of DNA. In this process, hydrogen bonds between the complementary base pairs are broken, leading to separation Melting temperature (Tm) of DNA- that temperature at which half of the DNA duplex gets dissociated to become single-stranded. Tm of DNA is between 85-95degC. *Primers with melting temperatures in the range of 52-58degC generally produce the best results. *Tm is propoional to G C pairs because there are three hydrogen bonds between G & C, as compared to the two hydrogen bonds between A & T. So more G C content gives thermostability to DNA. *For every 10 % increase in G C content, melting temperature raises by 5degC.