If a stretch of double-stranded DNA has a total of 560 nucleotides and 159 adenine nucleotides, what is the nucleotide composition of this DNA molecule? It has:

Question

If a stretch of double-stranded DNA has a total of 560 nucleotides and 159 adenine nucleotides, what is the nucleotide composition of this DNA molecule?  It has:

Quizplus · Accepted Answer

11ecba2d_0e73_61cb_a3bf_1f571a59fe98_MD0008_00 Purines (guanine or adenine) base pair with pyrimidines (cytosine or thymine) in DNA. Adenine (A) base pairs exclusively with thymine (T) via two hydrogen bonds, and guanine (G) base pairs with cytosine (C) via three hydrogen bonds. As a result, Chargaff's rules state that there is a 1:1 nucleotide mole ratio of pyrimidines to purines and that for any double-stranded DNA molecule: The amount of guanine equals the amount of cytosine, and the amount of adenine equals the amount of thymine (ie, G=C and A=T) The sum of purines equals the sum of pyrimidines (ie, G+A = C+T) If a stretch of DNA has 560 total nucleotides and 159 of these are adenine nucleotides, then there are also 159 thymine nucleotides (Choices A, B, and D). Nucleotide composition can be calculated as follows: Obtain the number of guanine and cytosine nucleotides by subtracting the number of adenine (159) and thymine (159) nucleotides from the total number of nucleotides (560). 560 - (2 x 159) = 560 - 318 = 242 nucleotides Divide 242 by 2 to obtain the number of guanine and cytosine nucleotides. 242/2 = 121 There are 121 guanine and 121 cytosine nucleotides in the described DNA. Educational objective: Chargaff's rules state that there is a 1:1 nucleotide mole ratio of pyrimidines to purines and that for any double-stranded DNA sample: A=T and G=C G+A = C+T

If a Stretch of Double-Stranded DNA Has a Total of 560