A stretch of double-stranded DNA is 1200 base pairs long…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A stretch of double-stranded DNA is base pairs long. Of these, are A-T pairs.
- How many A-T pairs are there?
- How many G-C pairs are there?
- How many hydrogen bonds hold the two strands together?
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. base pairs, of them A-T.
Plan. Count the two kinds of pair, then the bonds.
Step 1. (a) A-T pairs.
Step 2. (b) G-C pairs.
Step 3. (c) hydrogen bonds.
Answer: ; ; bonds.
Check. If every pair were A-T, there would be bonds. If every pair were G-C, there would be bonds. The answer lies between them.
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