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Ch. 16 - The Molecular Basis of Inheritance
Chapter 16, Problem 3

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

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Understand the base-pairing rules: In DNA, adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). This means that the number of A bases will equal the number of T bases, and the number of C bases will equal the number of G bases.
Analyze option a (A=G): This suggests that the number of adenine bases equals the number of guanine bases, which contradicts the base-pairing rules where A pairs with T and C pairs with G.
Analyze option b (A+G=C+T): This option is consistent with the base-pairing rules. Since A pairs with T and C pairs with G, the total number of purines (A and G) will equal the total number of pyrimidines (C and T).
Analyze option c (A+T=G+C): This option suggests that the sum of adenine and thymine bases equals the sum of guanine and cytosine bases. This is not necessarily true according to base-pairing rules, as it depends on the overall composition and sequence of the DNA.
Analyze option d (A=C): This suggests that the number of adenine bases equals the number of cytosine bases, which also contradicts the base-pairing rules.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Base-Pairing Rules

Base-pairing rules refer to the specific pairing of nitrogenous bases in DNA, where adenine (A) pairs with thymine (T) and guanine (G) pairs with cytosine (C). This complementary pairing is crucial for the structure of the DNA double helix and ensures accurate replication and transcription of genetic information.
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Chargaff's Rules

Chargaff's Rules

Chargaff's rules state that in a given DNA molecule, the amount of adenine equals the amount of thymine (A=T), and the amount of guanine equals the amount of cytosine (G=C). This principle underlies the base-pairing rules and is essential for understanding the stoichiometry of DNA bases in any sample.
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DNA Composition

The composition of DNA refers to the relative amounts of the four nitrogenous bases: adenine, thymine, guanine, and cytosine. Analyzing the composition helps in understanding the genetic makeup of an organism and can reveal insights into mutations, evolutionary relationships, and species identification.
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Related Practice
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In his work with pneumonia-causing bacteria and mice, Griffith found that a. the protein coat from pathogenic cells was able to transform nonpathogenic cells. b. heat-killed pathogenic cells caused pneumonia. c. some substance from pathogenic cells was transferred to nonpathogenic cells, making them pathogenic. d. the polysaccharide coat of bacteria caused pneumonia.

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Textbook Question

What is the basis for the difference in how the leading and lagging strands of DNA molecules are synthesized? a. The origins of replication occur only at the 5′ end. b. Helicases and single-strand binding proteins work at the 5′ end. c. DNA polymerase can join new nucleotides only to the 3′ end of a pre-existing strand, and the strands are antiparallel. d. DNA ligase works only in the 3′→5′ direction.

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Textbook Question

The elongation of the leading strand during DNA synthesis a. progresses away from the replication fork. b. occurs in the 3′→5′ direction. c. produces Okazaki fragments. d. depends on the action of DNA polymerase.

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Textbook Question

In a nucleosome, the DNA is wrapped around a. histones. b. ribosomes. c. polymerase molecules. d. a thymine dimer.

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