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Thirty percent (30%) of the nucleotide bases in human DNA are adenine (A) - HSC - SSCE Biology - Question 7 - 2009 - Paper 1
Question 7
Thirty percent (30%) of the nucleotide bases in human DNA are adenine (A). What is the percentage of guanine (G) bases in human DNA? (A) 20% (B) 30% (C) 40% (D)... show full transcript
Worked Solution & Example Answer:Thirty percent (30%) of the nucleotide bases in human DNA are adenine (A) - HSC - SSCE Biology - Question 7 - 2009 - Paper 1
Step 1
To find the percentage of guanine (G) bases in human DNA:
Answer
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Since adenine (A) bases constitute 30% of the total bases, the remaining bases (cytosine (C), guanine (G), and thymine (T)) account for 70% of the total.
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In DNA, adenine pairs with thymine (A with T) and guanine pairs with cytosine (G with C). Therefore, the percentage of guanine (G) must equal the percentage of cytosine (C).
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If we denote the percentage of guanine (G) as x, then the percentage of cytosine (C) is also x.
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Thus, we can set up the equation: 30% (A) + x (G) + x (C) + y (T) = 100%
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However, we can also assume that guanine (G) and cytosine (C) are equal, which gives us: 30% + 2x + 30% = 100%.
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Rearranging gives 2x = 40%, leading to x = 20%.
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Therefore, the percentage of guanine (G) bases in human DNA is 20%.