Two strands of DNA are linked together by hydrogen bonding between bases on each strand - AQA - A-Level Chemistry - Question 30 - 2019 - Paper 3
Question 30
Two strands of DNA are linked together by hydrogen bonding between bases on each strand.
Which row shows the number of hydrogen bonds between the pair of bases?
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Worked Solution & Example Answer:Two strands of DNA are linked together by hydrogen bonding between bases on each strand - AQA - A-Level Chemistry - Question 30 - 2019 - Paper 3
Step 1
Base 1: adenine, Base 2: guanine
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Answer
Adenine pairs with guanine, and this pair is known to have 2 hydrogen bonds.
Step 2
Base 1: cytosine, Base 2: thymine
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Answer
Cytosine pairs with thymine, which has 3 hydrogen bonds.
Step 3
Base 1: guanine, Base 2: cytosine
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Answer
Guanine pairs with cytosine, forming 3 hydrogen bonds.
Step 4
Base 1: adenine, Base 2: thymine
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Answer
Adenine pairs with thymine via 2 hydrogen bonds.
Step 5
Final Answer
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Answer
The correct answer is option C: guanine and cytosine, which have 3 hydrogen bonds.
