Chargaff's Rule, Definition, Case Pairing, and Importance

Chargaff's rule is a key concept in understanding the structure of DNA. It provided essential insight into the relationship between the nitrogenous bases in DNA, contributing to the discovery of the double-helix structure of DNA by Watson and Crick. For the NEET Exam , this rule is significant because it helps explain DNA replication and genetic variation, both of which are relevant for the exam.

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Definition of Chargaff's Rule

A = T and C = G

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Complementary Base Pairing

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Importance of Chargaff's Rule

• Chargaff's rule contributed to the discovery of the double helix structure of DNA. It explained why the two DNA strands could be complementary, with the base pairing between adenine and thymine, and cytosine and guanine, forming a stable structure.
• The rule ensures that during DNA replication, each strand can serve as a template to create an identical complementary strand. This guarantees the accurate duplication of genetic material in cell division.
• Chargaff's rule helps maintain genetic stability, ensuring that the genetic code is passed on correctly from one generation to the next. The pairing pattern supports the fidelity of DNA copying, minimizing the risk of errors or mutations.
• Chargaff's rule is fundamental in genetic research and the study of species differences. By comparing the base ratios in the DNA of different organisms, scientists can identify and classify species based on their genetic makeup.

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MCQs of Chargaff's Rule

Q1. Which of the following statement is correct?

1. Guanine pairs with cytosine through two H-bond
2. Pentose sugar and nitrogen base are linked through phosphoester linkage
3. Adenine does not pair with thymine.
4. Adenine pairs with thymine through two H-bonds.

Q2. Match the following List-I with List-II and choose the correct option.

List-I                                                     List-II

1. (A)-(III); (B)-(I); (C)-(II)
2. (A)-(II); (B)-(III); (C)-(I)
3. (A)-(I); (B)-(III); (C)-(II)
4. (A)-(II); (B)-(I); (C)-(III)

Q3. Statement-I: In a dsDNA, always a purine comes opposite to a pyrimidine.

Statement-II: Nitrogen bases are positioned linearly to the sugar-phosphate backbone and they face inside.

1. Statement I and Statement II both are correct.
2. Statement I is correct but Statement II is incorrect.
3. Statement I is incorrect but Statement II is correct.
4. Statement I and Statement-II both are incorrect.

Answers of MCQs of Chargaff's Rule