Final answer:
In a DNA strand with 35% adenine (A), there must also be 35% thymine (T) because of the rules of complementary base pairing where adenine pairs with thymine and guanine with cytosine.
Step-by-step explanation:
Understanding DNA Complementary Base Pairing
If a strand of DNA is composed of 35% adenine (A), it must also contain 35% thymine (T) due to the complementary base pairing rule discovered by Erwin Chargaff. Chargaff's rules state that the amount of adenine (A) is always equal to the amount of thymine (T), and the amount of guanine (G) is always equal to the amount of cytosine (C). Since DNA is a double helix, with each strand being a complement to the other, it is essential that the percentages of A and T, and G and C, match to form the correct base pairs that hold the two strands together with hydrogen bonds.
Note: This clarification is vital because there is a typographical error in one of the provided reference points, which incorrectly states that adenine pairs with cytosine and guanine pairs with thymine. The correct base pairing is adenine with thymine and guanine with cytosine.
In conclusion, for the given DNA strand, if there's 35% adenine, the same strand must also contain 35% thymine. The remaining 30% would be split equally between guanine (G) and cytosine (C), each being 15%