In a double-stranded DNA molecule, the percentage of Guanine can never be more than ___%. Why?

In a double-stranded DNA molecule, the percentage of Guanine (G) can never be more than 50%.

This is because DNA is composed of two complementary strands, where each base pairing consists of Adenine (A) with Thymine (T), and Guanine (G) with Cytosine (C). The two strands are held together by hydrogen bonds between these base pairs.

The total percentage of G and C collectively is equal to the total percentage of A and T. When DNA is denatured, or separated into single strands, the percentage of G in one strand will be equal to the percentage of C in the other strand, since they pair together. Similarly, the percentage of A in one strand will be equal to the percentage of T in the other strand.

Hence, the G percentage can never exceed 50% in a double-stranded DNA molecule because the percentage of C would be equal to G, and collectively they would make up 100% of the GC pairs.