In analyzing the number of different bases in a DNA sample, which result would be consistent with the ­ base-pairing rules?
a. A=G
b. A+G=C+T
c. A+T=G+C
d. A=C

Verified step by step guidance

1. Understand the base-pairing rules in DNA: Adenine (A) pairs with Thymine (T), and Guanine (G) pairs with Cytosine (C). This means the amount of A should equal the amount of T, and the amount of G should equal the amount of C.
2. Consider the option A=G. This would imply that the amount of Adenine is equal to the amount of Guanine, which contradicts the base-pairing rules since A pairs with T, not G.
3. Evaluate the option A+G=C+T. This option suggests that the sum of Adenine and Guanine equals the sum of Cytosine and Thymine. This is consistent with the base-pairing rules because A pairs with T and G pairs with C, so the total number of purines (A and G) should equal the total number of pyrimidines (C and T).
4. Analyze the option A+T=G+C. This implies that the sum of Adenine and Thymine equals the sum of Guanine and Cytosine. While this might seem consistent at first glance, it does not necessarily follow the base-pairing rules directly, as it does not account for the specific pairing of A with T and G with C.
5. Consider the option A=C. This suggests that the amount of Adenine is equal to the amount of Cytosine, which contradicts the base-pairing rules since A pairs with T, not C.

Key Concepts

Base Pairing Rules

Base pairing rules in DNA refer to the specific pairing between nitrogenous bases: adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C). This complementary base pairing is due to hydrogen bonding, where A forms two hydrogen bonds with T, and G forms three hydrogen bonds with C, ensuring the DNA double helix structure is stable and consistent.

Chargaff's Rule

Chargaff's Rule states that in a DNA molecule, the amount of adenine (A) is equal to thymine (T), and the amount of guanine (G) is equal to cytosine (C). This rule is derived from the base pairing rules and implies that the total purines (A+G) equal the total pyrimidines (C+T), maintaining a consistent ratio across different organisms.

DNA Structure

DNA is structured as a double helix, composed of two strands running in opposite directions. Each strand is made up of a sugar-phosphate backbone and nitrogenous bases. The specific pairing of bases (A with T and G with C) across the two strands allows for the replication and transmission of genetic information, as each strand can serve as a template for creating a new complementary strand.