Can someone explain why the answer is Guanine 3.A type of bacteria is discovered
ID: 190251 • Letter: C
Question
Can someone explain why the answer is Guanine 3.A type of bacteria is discovered in which the genetic material is a single, circular molecul double-stranded DNA in which one of the bases (either A, T, C, or G) is sometimes modified by the addition of a methyl(-CH3) group. In analyzing the DNA of this organism, the individual strands of the circular DNA molecule are first separated and then the base composition of each strand determined. One strand consists of 22% A, 26% T, 18% C, 30% G, and 496 M: th strand consists of 26% A, 22% T, 25% C, 22% G, and 596 M, where "M" representsthe chemically modified bases. Which base in double-stranded DNA does M pair with? e other A. cytosine , guanine C. adenine D. thymineExplanation / Answer
The answer is G.
As per Chargaff's rule [A]=[T], and [C]=[G] in the opposite strands.
The [A]=[T] rules apply which means they pair with each other. This means the methylated residue either pairs with [G] or [C]. No for the first strand where there are 4 [M] exactly 4 extra [G] are present (as only 18 cytosine are there so 4 guanosine are being left). Similarly, the second strand has 5 [M] and 5 extra [G] are present (as only 25 cytosine are there so 5 guanosine are being left). Thus it can be concluded that M pairs with guanosine.