Question

In his analysis of different species’ DNA, E.Chargaff discovered the base-pairing rules of DNA.

1.) Chargaff’s rules state: The amount of adenine is equal to ? and the amount of cytosine is equal to ? .
2.) if a sample of jellyfish DNA is 14% cyotsine, approximately how much adenine would there be in that same sample? Show your work.

Answer 1

1. Thymine, Guanine

2. 36% Adenine

Step-by-step explanation:

1. Edwin Chargaff, who proposed the complementary base pairing rule, stated in his rule that the amount of purine bases (Adenine and Guanine) is equal to the amount of Pyrimidine bases (Cytosine and Thymine). This means that, in a DNA molecule, the amount of adenine is always equal to Thymine (A=T) and the amount of Cytosine is equal to Guanine (G=C).

Also, the total amount of the four nucleotide bases that make up a DNA molecule is equal to 1 or 100% i.e. A+T+G+C= 100%

2. Based on the rule above, if a sample of jelly fish DNA contains 14% Cytosine, the amount of its complementary pair (Guanine) will also be 14%.

Hence, Cytosine and Guanine will collectively occupy 14+14=28% of the DNA.

To find the amount of the other two bases i.e. Adenine and Thymine, we subtract 28% from 100%

That is, 100 - 28 = 72%

If both Adenine and Thymine contains 72% and each must be equal, we divide 72% by 2 to get the amount of each.

Hence, 72/2 = 36% of Adenine and 36% of Thymine.

According to the question, Adenine will contain 36% in the Jellyfish DNA.