Question

dna and rna structureperiod: ________ date: ________assignment – student editionvi. a sequence of dna (shown to the right) was found to have adenine (a) repeated 300 times. state how many times the following nucleotides would appear1. cytosine (c)2. thymine (t)3. guanine (g)4. explain how you worked out your answers to questions 1, 2 and 3.copyright © iteachly.com5

Explanation:

Step1: Apply base pairing rule for T

In DNA, adenine (A) pairs with thymine (T), so their counts are equal.
$n(T) = n(A) = 300$

Step2: Analyze sample DNA ratio

From the DNA diagram, the ratio of A:T:C:G is 2:2:2:2, so $n(C)=n(G)$, and $n(A)+n(T) = n(C)+n(G)$.

Step3: Calculate total of C+G

Total of A and T: $300 + 300 = 600$, so $n(C)+n(G)=600$.

Step4: Solve for C and G

Since $n(C)=n(G)$, divide total by 2:
$n(C) = \frac{600}{2} = 300$
$n(G) = \frac{600}{2} = 300$

Answer:

1. Cytosine (C): 300
2. Thymine (T): 300
3. Guanine (G): 300
4. DNA follows Chargaff's base pairing rules: adenine (A) always pairs with thymine (T), so their counts are equal (300 each). The sample DNA shows equal ratios of all four bases, so the total number of cytosine (C) and guanine (G) equals the total of A and T. Since C pairs with G, they are also equal, so each is 300.