As suggested by the thermodynamic parameters, increasing the GC content for this
ID: 275385 • Letter: A
Question
As suggested by the thermodynamic parameters, increasing the GC content for this length of nucleic acid ________ the disorder of the system, which favors the ____________.
increases; melting of duplex DNA
increases; formation of duplex DNA
decreases; melting of duplex DNA
decreases; formation of duplex DNA
Therefore, the thermodynamic parameters indicate that the _______ of duplex DNA is enthalpically opposed and entropically favored, while the _________ of duplex DNA is enthalpically favored and entropically opposed (hint: see the discussion of entropy in Chapter 1).
Therefore, the thermodynamic parameters indicate that the _______ of duplex DNA is enthalpically opposed and entropically favored, while the _________ of duplex DNA is enthalpically favored and entropically opposed (hint: see the discussion of entropy in Chapter 1).
melting; formation formation; meltingExplanation / Answer
Option 'd' is the correct answer.
As suggested by the thermodynamic parameters, increasing the GC content for this length of nucleic acid decreases the disorder of the system, which favors the formation of duplex DNA. The GC pair is bound by 3 hydrogen bonds as compared to AT pair which is bound by only 2 hydrogen bonds, thus a nucleotide sequence with high GC content will be relatively more stable than a sequence rich in AT pair. The destabilizing entropic effects are more prominent in bases with the formation of second and third hydrogen bonds, which leads to decrease in the disorder of the system. Also, GC pairs have more favourable base stacking energy because of the relative positions of exocyclic groups than in the A:U pairs, which favours the formation of duplex DNA. Higher the GC content, higher the melting temperature (Tm) of the nucleotide sequence.
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