If a portion of a strand of DNA bases reads 5' AGCTAGCGT 3', what would the sequence of bases on the complementary strand read?

Rationale

3' TCGATCGCA 5'

The complementary DNA strand is formed by pairing each base with its matching counterpart: adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). Therefore, for the original sequence 5' AGCTAGCGT 3', the complementary sequence reads 3' TCGATCGCA 5'.

A (3' AGCTAGCGT 5') YOUR ANSWER

This choice is incorrect because it presents the same sequence as the original strand but in the reverse orientation. The complementary strand should contain the correct base pairs rather than repeating the original sequence.

B (5' UCGAUCGCA 3') YOUR ANSWER

This option incorrectly uses uracil (U) instead of thymine (T), which is not present in DNA. Uracil is found in RNA, and the question pertains specifically to a DNA sequence, making this choice invalid.

C (3' TCGATCGCA 5') CORRECT

This choice correctly reflects the complementary base pairing of the original DNA strand. Each base is paired with its complement: A with T, C with G, and the sequence is written in the correct 3' to 5' orientation.

D (5' TCGUTCGCU 3') YOUR ANSWER

This option incorrectly includes uracil (U) instead of thymine (T), similar to option B. Since the question specifies a DNA sequence, the presence of uracil disqualifies this answer as a valid complementary strand.

Conclusion

The complementary DNA strand is determined by pairing each base with its appropriate complement, taking into account the correct orientation. In this case, the correct complementary sequence to the original strand 5' AGCTAGCGT 3' is 3' TCGATCGCA 5'. The other options either misrepresent the base pairs or incorrectly incorporate RNA components, highlighting the importance of accurate base pairing in DNA structure.

If a portion of a strand of DNA bases reads 5' AGCTAGCGT 3', what would the sequence of bases on the complementary strand read?

3' TCGATCGCA 5'

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