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In a sample of DNA, 23% of the bases are cytosine - OCR Gateway - GCSE Biology - Question 8 - 2020 - Paper 1
Question 8
In a sample of DNA, 23% of the bases are cytosine. What percentage of the bases are adenine? A 23% B 27% C 46% D 54% Your answer
Worked Solution & Example Answer:In a sample of DNA, 23% of the bases are cytosine - OCR Gateway - GCSE Biology - Question 8 - 2020 - Paper 1
Step 1
What percentage of the bases are adenine?
Answer
To find the percentage of adenine in the DNA, we must consider the base pairing rules. In DNA, adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G).
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Identify Given Information: We know that 23% of the bases are cytosine (C). Since the amount of guanine (G) is equal to the amount of cytosine (C), we conclude that 23% of the bases are also guanine.
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Calculate Percentage of Total Bases: The percent composition of bases in DNA must total 100%. Therefore, we have:
%A + %T + %C + %G = 100%
Given that %C = 23% and %G = 23%, we can simplify this to:
%A + %T + 23 ext{%} + 23 ext{%} = 100 ext{%}
Which simplifies to: %A + %T = 54 ext{%}
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Using Base Pairing Rules: Since adenine pairs with thymine, we know %A = %T. Let %A = %T = x. Thus, we have: 2x = 54 ext{%}
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Solving for x: x = 27%. Therefore, %A (adenine) = 27%.
Hence, the answer to the question is B 27%.