Which of the following equalities is not true for double-stranded DNA?
(G+C)=(A+T)

Verified step by step guidance

1. Understand the structure of double-stranded DNA: DNA is composed of two complementary strands, where adenine (A) pairs with thymine (T) and guanine (G) pairs with cytosine (C). This pairing is governed by Chargaff's rules.
2. Recall Chargaff's rules: In double-stranded DNA, the amount of adenine (A) is equal to the amount of thymine (T), and the amount of guanine (G) is equal to the amount of cytosine (C). Mathematically, this can be expressed as A = T and G = C.
3. Analyze the given equality: The problem states (G + C) = (A + T). This implies that the total number of guanine and cytosine bases is equal to the total number of adenine and thymine bases.
4. Evaluate the equality based on Chargaff's rules: While A = T and G = C individually hold true, there is no requirement for (G + C) to equal (A + T). The proportions of G+C and A+T can vary depending on the organism's genome composition.
5. Conclude that the equality (G + C) = (A + T) is not universally true for double-stranded DNA, as the GC content and AT content can differ across species.

Key Concepts

Base Pairing Rules

In double-stranded DNA, the base pairing rules dictate that adenine (A) pairs with thymine (T) and guanine (G) pairs with cytosine (C). This complementary pairing is crucial for the stability of the DNA structure and ensures accurate replication and transcription processes.

Chargaff's Rules

Chargaff's rules state that in a double-stranded DNA molecule, the amount of adenine is equal to thymine (A=T) and the amount of guanine is equal to cytosine (G=C). This leads to the conclusion that the total amount of purines (A+G) equals the total amount of pyrimidines (C+T), but does not imply that (G+C) equals (A+T) in all cases.

DNA Composition

The composition of DNA varies among different organisms and can affect the ratios of the nucleotide bases. While the sum of G and C may not equal the sum of A and T in all species, the overall structure and function of DNA remain consistent, highlighting the diversity of genetic material across life forms.