A double-stranded DNA molecule contains 2000 base pairs. If 20% of the nucleotides are guanine (G), how many adenine (A) nucleotides are in the molecule?

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1600

1200

1400

2400

answer is A.

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Detailed Solution

Since the DNA molecule is double-stranded, the percentage of G nucleotides should be equal to the percentage of cytosine (C) nucleotides. Therefore, the combined percentage of G and C is 40% (20% G + 20% C). The remaining 60% must be the percentage of A and thymine (T) nucleotides.

To determine the number of A nucleotides in the DNA molecule, we need to know the total number of nucleotides. Since the molecule has 2000 base pairs, it has 4000 nucleotides (two nucleotides per base pair).

The percentage of A nucleotides can be calculated as follows:

% A = 60% / 2 = 30%

Therefore, the number of A nucleotides in the molecule is:

Number of A nucleotides = 30% x 4000 = 1200

Answer: There are 1200 adenine nucleotides in the DNA molecule.

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