A piece of double-stranded DNA, which is 200 base pairs in length, contains 50 thymine bases - VCE - SSCE Chemistry - Question 9 - 2008 - Paper 1
Question 9
A piece of double-stranded DNA, which is 200 base pairs in length, contains 50 thymine bases.
The number of guanine bases in the piece of DNA is
A. 50
B. 100
C. 125
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Worked Solution & Example Answer:A piece of double-stranded DNA, which is 200 base pairs in length, contains 50 thymine bases - VCE - SSCE Chemistry - Question 9 - 2008 - Paper 1
Step 1
Calculate the total base pairs
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Answer
The total length of the DNA is 200 base pairs.
Step 2
Identify the number of adenine bases
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Answer
In double-stranded DNA, adenine (A) pairs with thymine (T). Therefore, if there are 50 thymine bases, there must also be 50 adenine bases.
Step 3
Determine remaining bases
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Answer
Since there are 50 adenine and 50 thymine bases, the combined total of A and T is 100 bases. Thus, the total number of guanine (G) and cytosine (C) bases is 200 - 100 = 100 bases.
Step 4
Consider base pairing
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Answer
In double-stranded DNA, guanine (G) pairs with cytosine (C). Therefore, the number of guanine and cytosine bases is equal.
Step 5
Calculate the number of guanine bases
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Let the number of guanine bases be represented as G, then cytosine bases will also be G. Since G + C = 100, we have 2G = 100, leading to G = 50. Thus, there are 50 guanine bases.
Step 6
Finalize answer
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Answer
Since the calculated number of guanine bases is 50, the answer is:
A. 50
