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Question
In a double-stranded DNA, the sequence of base pairs in one strand is AGCTAAGC. What is the complementary sequence on the other strand?
In a double-stranded DNA, the sequence of base pairs in one strand is AGCTAAGC. What is the complementary sequence on the other strand?
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Solution
The correct option is A TCGATTCG
According to Watson and Crick model, DNA has four nitrogenous bases, that includes two purines and two pyrimidines, in its nucleotide chains. The purines are adenine and guanine and pyrimidines are namely cytosine, thymine. In a dsDNA, a purine always pairs with a pyrimidine and a pyrimidine base pairs with purine base only; thus, adenine pairs with thymine (A-T) and guanine pairs with cytosine (G-C). A DNA strand with sequence "AGCTAAGC" will have a complementary strand with the sequence "TCGATTCG". Uracil (U) is a pyrimidine base that is present in RNA in place of T; it is not found in DNA. The sequence given in option B and D have "U", which makes them wrong. A DNA strand cannot have the same base sequence in its complementary strand; thus option C is wrong.
According to Watson and Crick model, DNA has four nitrogenous bases, that includes two purines and two pyrimidines, in its nucleotide chains. The purines are adenine and guanine and pyrimidines are namely cytosine, thymine. In a dsDNA, a purine always pairs with a pyrimidine and a pyrimidine base pairs with purine base only; thus, adenine pairs with thymine (A-T) and guanine pairs with cytosine (G-C). A DNA strand with sequence "AGCTAAGC" will have a complementary strand with the sequence "TCGATTCG". Uracil (U) is a pyrimidine base that is present in RNA in place of T; it is not found in DNA. The sequence given in option B and D have "U", which makes them wrong. A DNA strand cannot have the same base sequence in its complementary strand; thus option C is wrong.
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