Which one of the following statement is incorrect regarding the work of Erwin Chargaff?
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Chargaff's rules can be summarized in two main points: 1) A=T and G=C, so Purines=Pyrimidines. 2) The exact percentage of these bases varies between different species. The incorrect statement violates the second point.
The base composition of DNA don't varies from one species to another.
DNA specimens isolated from different tissues of the same species have the same base composition.
The base composition of DNA in a given species does not change with an organism's age, nutritional state, or changing environment.
The sum of the purine residues equals the sum of the pyrimidine residues; that is, A + G = T + C.
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The Correct Option isA
Solution and Explanation
Step 1: Understanding the Concept:
Erwin Chargaff's experiments on the base composition of DNA led to the formulation of "Chargaff's rules," which were crucial for Watson and Crick's discovery of the DNA double helix structure. We need to identify the statement that contradicts these rules. Step 2: Detailed Explanation:
Let's analyze each statement in the context of Chargaff's findings:
(A) The base composition of DNA don't varies from one species to another. This statement is incorrect. A key finding by Chargaff was that the relative amounts of A, G, C, and T bases do vary from one species to another. For example, the ratio of (A+T) to (G+C) is different in humans compared to E. coli.
(B) DNA specimens isolated from different tissues of the same species have the same base composition. This is correct. Chargaff found that for a given species, the DNA base composition is consistent across all tissues.
(C) The base composition of DNA in a given species does not change with an organism's age, nutritional state, or changing environment. This is correct. The base composition is a stable characteristic of a species.
(D) The sum of the purine residues equals the sum of the pyrimidine residues; that is, A + G = T + C. This is correct. This is the most famous of Chargaff's rules, often stated as the amount of adenine (A) equals the amount of thymine (T), and the amount of guanine (G) equals the amount of cytosine (C). This implies A+G (purines) = T+C (pyrimidines).
Step 3: Final Answer:
The incorrect statement is (A), as it directly contradicts one of Chargaff's primary discoveries.
