Question

Recall that two hydrogen bonds bind A and T, but three hydrogen bonds bind G and C. The stability of DNA is affected by the number of hydrogen bonds, with more bonds promoting more stability. Double-stranded DNA molecules that have greater stability require more heat to be broken into single strands. Which double-stranded DNA molecules would likely require the lowest temperature in PCR?A. A molecule with 16 percent A B. A molecule with 23 percent T C. A molecule with 30 percent C D. A molecule with 35 percent G E. More information is required to answer this question

Answer 1

A) A molecule with 16 percent A

Step-by-step explanation:

Two hydrogen bonds are present between adenine and thymine(A=T).

The higher the number of hydrogen bonds, the stronger the bonds between the organic bases, holding the DNA strands, the higher the resistance of the DNA double strands to heat, and thus the higher the stability of the DNA structure to temperature.

Therefore, according to Chargaff's rule; the amount of adenine is always equal to thymine, thus 16 % Adenine will provide 16% Thymine in the complementary DNA strands structure. Thus the percentages of 2-hydrogen bonds A=T is higher in the DNA double strands structure.

Consequently, if the number of hydrogen bonds between bases determine the stability of DNA strands, then a DNA strands with more 2- hydrogen bonds of 16 % adenine=thymine will have low stability and therefore lowest temperature in PCR.

Answer 2

A molecule with 35 percent

Step-by-step explanation:

With more bonds, more heat is required to break the bonds. Hence more heat is required to break C:G with three bonds compared to A:T with two bonds.

Since A:T are bonded, likewise, C:G, they will have the same proportion in DNA, i.e. a molecule with 16 percent A will also have 16 percent of T. This means that A:T is 32% (16+16).

If A:T is 32%, the other bases will be 100% - 32% = 68%

So, C:G will be 68%.

Recall that C:G will also have equal proportion.

Therefore the proportion of C is 68/2=34% (same as G).

Recall that A:T is joined by two bonds and C:G is joined by three bonds.

In option D, 35% G means that C:G is 70% and A:T is 30% (100%-7-%).

Hence a molecule with 70% of C:G will require more heat than that with 68% C:G.