Question

If a DNA molecule is found to be composed of 40% thymine, what percentage of guanine would be expected.

Answer 1

Answer:

10%

Explanation:

Chargaff postulated the complementary base pairing rule, where he stated that in the DNA molecule, Adenine (A) will always pair with Thymine (T) and Guanine (G) with Cytosine (C) i.e. A-T, G-C

Chargaff stated that the concentration of purines (Adenine and Guanine) is always equal to that of pyrimidines (Thymine and Cytosine) i.e. {A} + {G} = {C} + {T}

These equal concentration equals 100% in totality i.e. A+G+C+T= 100%

Thymine pairs with Adenine, if there is 40% of Thymine in the DNA molecule, it means there will be 40% of Adenine also. 40 + 40 = 80%. This leaves us with 100-80 = 20% for Guanine and Cytosine.

Since there will be an equal amount of Guanine and Cytosine too, Guanine will therefore, be 20/2 = 10%.

That is, 10% Guanine, 10% Cytosine.

Answer 2

If a DNA molecule is found to be composed of 40% thymine, the percentage of guanine would be expected - 10%

Chargaff's rule

• the DNA from any cell of all organisms should have a 1:1 ratio of purine bases and pyrimidine bases.
• Purines are adenine and thymine in DNA and pyrimidines are guanine and cytosine.

• The amount of guanine should be equaled to cytosine and the amount of adenine should be equaled to thymine.

Given is - 40% of thymine.

• If you have 40% of thymine then you have 40% of adenine because the amount of adenine and thymine is equal.
• 40% plus 40% is 80% of adenine and thymine.
• From 100% DNA bases subtract 80% and you will get 20%.
• Then divide this by 2 and you will get 10%.
• 10% of guanine and 10% of cytosine, because their amounts are equal in the DNA strand.

Thus, If a DNA molecule is found to be composed of 40% thymine, the percentage of guanine would be expected - 10%

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