Question

Given the DNA sequence 5’ CCTAGAA 3’, the complementary strand would read:

• A. 3’ GGATCTT 5’
• B. 3’ AAGATCC 5’
• C. 5’ GGTATTC 3’
• D. 5’ GGATCTT 3’

Answer 1

The correct option is A

3’ GGATCTT 5’

Adenine (A) and guanine (G) are the purines, while thymine (T) and cytosine (C) are the pyrimidines in DNA. A purine always pairs up with a pyrimidine. A and T form a pair, and so do G and C. A base on one DNA strand would form a base pair with its respective counterpart in the complementary strand. The two DNA strands would also run in opposite directions; one of them would be in the 5’-->3’ direction, while the complementary strand would run in the 3’-->5’ direction.