Textbook Question
Which of the following equations are true for the percentages of nucleotides in double-stranded DNA?
(A+G)/(C+T)=1.0
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7. DNA and Chromosome Structure
DNA Structure
1:40 minutesProblem 17a
Textbook Question
Which of the following equalities is not true for double-stranded DNA?
(G+T)=(A+C)
Verified step by step guidance1
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 is known as Chargaff's rule.
Recall Chargaff's rule: In double-stranded DNA, the amount of adenine (A) equals the amount of thymine (T), and the amount of guanine (G) equals the amount of cytosine (C). Mathematically, this can be expressed as A = T and G = C.
Combine the base pair relationships: Since A = T and G = C, the total purines (A + G) will equal the total pyrimidines (T + C). This can be expressed as (A + G) = (T + C).
Analyze the given equality: The problem asks whether the equality (G + T) = (A + C) is true. Rearrange the bases into purines and pyrimidines to check if this equality aligns with Chargaff's rule.
Conclude based on Chargaff's rule: If the equality (G + T) = (A + C) does not align with the purine-pyrimidine balance established by Chargaff's rule, then it is not true for double-stranded DNA.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
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.
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Chargaff's Rules
Chargaff's rules state that in any given DNA molecule, the amount of adenine equals thymine (A = T) and the amount of guanine equals cytosine (G = C). This leads to the conclusion that the total amount of purines (A + G) equals the total amount of pyrimidines (C + T), which is essential for understanding the stoichiometry of DNA.
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DNA Composition
The composition of DNA includes four nucleotide bases: adenine, thymine, guanine, and cytosine. The equality (G + T) = (A + C) reflects the balance of these bases in a double-stranded DNA molecule, which is critical for maintaining the integrity and function of genetic information.
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