If one strand of a DNA has the sequence ATGCTTCA, sequence of the bases in complementary strand is :

Solution

Chemistry ma’am · 3 steps

Go base by base and swap each one for its partner: A pairs with T, and G pairs with C.

1. Pairing rule. In DNA, adenine always pairs with thymine through 2 hydrogen bonds. Guanine always pairs with cytosine through 3 hydrogen bonds. So A ↔ T and G ↔ C.
2. Swap each base. Read the given strand one base at a time: A → T, T → A, G → C, C → G, T → A, T → A, C → G, A → T.

   A T G C T T C A ; T A C G A A G T

3. So. The complementary strand reads TACGAAGT, which is option (b).

The idea to keep. A complementary strand is never a copy. Each base is replaced by its partner, A with T and G with C, and you keep the same order.

Answer from the NTA final answer key. Solution by PrepWiser.