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Chapter 25: Problem 30

The "melting point" of a DNA molecule is the temperature at which the double- helical strand breaks apart. Suppose you are given two DNA samples. One sample contains 45 percent C-G base pairs while the other contains 64 percent C-G base pairs. The total number of bases is the same in each sample. Which of the two samples has a higher melting point? Why?

Short Answer

Expert verified
The DNA sample with 64% C-G base pairs has a higher melting point because C-G base pairs, forming three hydrogen bonds, contribute more to the DNA molecule's stability than A-T base pairs, which form only two hydrogen bonds.

Step by step solution

01

Understanding DNA base pairs

DNA has four bases: adenine (A), thymine (T), cytosine (C), and guanine (G). Adenine pairs with thymine through two hydrogen bonds, while cytosine pairs with guanine through three hydrogen bonds.
02

Relate base pairs to DNA melting point

The strength of DNA base pairing is determined by the number of hydrogen bonds. This means that C-G base pairs, with three hydrogen bonds, contribute more to the stability of the DNA molecule than A-T base pairs. As a result, DNA samples with a higher C-G percentage will have a higher melting point.
03

Compare DNA samples

We know that a DNA sample with 45% C-G pairs and another with 64% C-G pairs have the same total number of bases. Thus, the sample with 64% C-G pairs has more C-G pairs, i.e., more three-bonded pairs, which contributes to a higher melting point.

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Most popular questions from this chapter

The following are data obtained on the rate of product formation of an enzyme- catalyzed reaction: $$ \begin{array}{cc} \hline \text { Temperature }\left({ }^{\circ} \mathbf{C}\right) & \begin{array}{c} \text { Rate of Product } \\ \text { Formation }(M / s) \end{array} \\ \hline 10 & 0.0025 \\ 20 & 0.0048 \\ 30 & 0.0090 \\ 35 & 0.0086 \\ 45 & 0.0012 \\ \hline \end{array} $$ Comment on the dependence of rate on temperature. (No calculations are required.)

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