Question 20

The complementary strand of DNA would read 3' TCGATCGGA 5'

The sequence of bases on the complementary strand is 3' TCGATCGGA 5', which pairs with the original strand of DNA through base pairing rules, where adenine pairs with thymine and cytosine pairs with guanine.

A) 5' UCGUAGCCA 3'

This option is incorrect as it represents an RNA sequence, not a complementary DNA strand. In DNA, thymine (T) is present instead of uracil (U), which makes this option invalid.

B) 5' TCGTACGGT 3'

This option is also incorrect. Although it starts with thymine, the sequence does not correctly complement the original DNA strand provided, failing to follow proper base pairing.

C) 3' AGCTAGGGT 5'

This option is incorrect because it is an exact copy of the original strand, merely reversed in direction. The complementary strand must consist of bases that pair correctly with those of the original strand.

D) 3' TCGATCGGA 5'

This option is correct as it is the properly base-paired complementary sequence to the original strand. Adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C), yielding the correct complementary bases.

Conclusion

The correct answer is D) 3' TCGATCGGA 5' because it accurately reflects the complementary base pairing with the original DNA strand. All other options either misrepresent the base pairing rules or fail to provide a complementary sequence. Thus, option D is the only one that aligns with the principles of DNA complementarity.