## anonymous one year ago Given DNA structure, would a DNA strand with more adenine and guanine be more stable, or would a DNA strand with more cytosine and thymine be more stable?

1. anonymous

Are you sure you typed that in correctly? @mathmaticalmolly

2. Koikkara

$$\color{blue}{\huge\tt{DNA ~Structure:}}$$The base–pairs in DNA are adenine-thymine (A-T) and cytosine-guanine (C-G). DNA contains deoxyadenosine (deoxyribose sugar bonded to adenine), deoxyguanosine (deoxyribose sugar bonded to guanine), deoxycytidine (deoxyribose sugar bonded to cytosine), and deoxythymidine (deoxyribose sugar bonded to thymine).

3. Koikkara

$$\color{blue}{\huge\tt{Reference~(in~case)}}$$ http://highered.mheducation.com/sites/9834092339/student_view0/chapter14/dna_structure.html

4. Koikkara

$$\color{red}{\huge\tt{Stability:}}$$ When working on the structure of DNA, $$\large \mathcal{Watson~ and~ Crick}$$, figured out that the two polynucleotides in the DNA (i.e., the DNA strands) interacted through the bases, they also deduced, with the help of Chargraff's rules, that the bases were pretty picky as to whom they interacted with. $$Nucleotides$$ containing Adenine (A) would only interact with nucleotides containing Thymine (T), while nucleotides containing Cytosine (C) would only interact with nucleotides containing Guanine (G). $$Which ~Means:$$ Only two kinds of base pairs were $$\color{blue}{\large \tt{possible~GC (or CG) and ~AT (or TA)}}$$ . So, the two strands of DNA are said to 'complement each other'. This is what we call complementary base pairing. $$Picture:$$ Complementary base pairing explains Chargraff's findings. As Adenine always associates with Thymine, the number of As and Ts in DNA must always be the same. You can remember which base associates with which by using the mnemonic GCAT. @MathmaticalMolly From this we understand, the pairing between adenine and guanine or cytosine $$and$$ thymine will not be stable $$or$$ will not be possible. $$Hope~it~was~clear~for~you~!!$$

5. Koikkara

$$\color{blue}{\huge\tt{Nice~}}$$ $$\huge\mathcal{to~meet~}$$ $$\color{red}{\huge\tt{You~!}}$$

6. aaronq

Good information, but you're missing the point that one pair (AT or GC) will be more stable over the other. In one of the attachments you'll see that the GC pair has 3 hydrogen bonds holding them together, while the AT pair only has 2. Because of the larger number of H-bonds, GC pair is more stable. By stable they mean less susceptible for it to break apart/away. The nitrogenous bases (A, G, T ,C) absorb UV light strongly when they're not paired (because of their conjugated (aromatic) structure), but when paired they no longer absorb - this is called the hyperchromic effect. An experiment can be done to show the stability of the GC pair over the AT pair, synthesize two DNA strands of equal GC and AT pair content, you'll see 50% of absorption at one temperature and 50% at the other. The first (lower) temperature will indicate the melting of the A-T pair and the higher temp the GC pair |dw:1443871594366:dw|

7. anonymous

@aaronq Has it absolutely right, which is why I asked if the question is written correctly. A high C-G percentage does provide slightly more heat resistance compared to a DNA strand with a significantly lower C-G percentage.