Two samples of double-stranded DNA were analysed…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Two samples of double-stranded DNA were analysed.
Sample 1 has adenine.
Sample 2 has of its bases as G and C together.
- In sample 1, what per cent is thymine?
- In sample 1, what per cent is guanine?
- In sample 2, what per cent is adenine?
Need a reminder? The key ideaShow
In a double-stranded DNA, A equals T and G equals C, so the purines equal the pyrimidines. A pairs with T by 2 hydrogen bonds. G pairs with C by 3 hydrogen bonds. The two strands run in opposite directions. A single strand, or an RNA with uracil, does not follow the rule.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. Sample 1: A. Sample 2: G + C.
Plan. Use A T and G C, and a total of .
Step 1. (a) Thymine equals adenine, so T is .
Step 2. (b) A and T together are . G and C share , so G is .
Step 3. (c) A and T share , so A is .
Answer: ; ; .
Check. In sample 1 the purines are , and the pyrimidines are .
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