Textbook Question
List the order in which the following proteins and enzymes are active in E. coli DNA replication: DNA pol I, SSB, ligase, helicase, DNA pol III, and primase.
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Ch. 7 - DNA Structure and Replication
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172
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Table of contents
- Ch. 1 - The Molecular Basis of Heredity, Variation, and Evolution64
- Ch. 2 - Transmission Genetics144
- Ch. 3 - Cell Division and Chromosome Heredity81
- Ch. 4 - Gene Interaction87
- Ch. 5 - Genetic Linkage and Mapping in Eukaryotes103
- Ch. 6 - Genetic Analysis and Mapping in Bacteria and Bacteriophages73
- Ch. 7 - DNA Structure and Replication71
- Ch. 8 - Molecular Biology of Transcription and RNA Processing79
- Ch. 9 - The Molecular Biology of Translation110
- Ch. 10 - Eukaryotic Chromosome Abnormalities and Molecular Organization100
- Ch. 11 - Gene Mutation, DNA Repair, and Homologous Recombination86
- Ch. 12 - Regulation of Gene Expression in Bacteria and Bacteriophage90
- Ch. 13 - Regulation of Gene Expression in Eukaryotes38
- Ch. 14 - Analysis of Gene Function via Forward Genetics and Reverse Genetics72
- Ch. 15 - Recombinant DNA Technology and Its Applications69
- Ch. 16 - Genomics: Genetics from a Whole-Genome Perspective49
- Ch. 17 - Organelle Inheritance and the Evolution of Organelle Genomes27
- Ch. 18 - Developmental Genetics43
- Ch. 19 - Genetic Analysis of Quantitative Traits66
- Ch. 20 - Population Genetics and Evolution at the Population, Species, and Molecular Levels105
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
Chapter 7, Problem 21
Raymond Rodriguez and colleagues demonstrated conclusively that DNA replication in E. coli is bidirectional. Explain why locating the origin of replication on one side of the circular chromosomes and the terminus of replication on the opposite side of the chromosome supported this conclusion.
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Understand the structure of the E. coli chromosome: It is a circular DNA molecule, meaning that replication can proceed in either one or two directions from the origin of replication (OriC).
Recall the concept of bidirectional replication: In bidirectional replication, DNA synthesis occurs in two opposite directions from the origin of replication, eventually meeting at the terminus of replication.
Consider the experimental setup: Raymond Rodriguez and colleagues identified the origin of replication (OriC) on one side of the circular chromosome and the terminus of replication (Ter) on the opposite side.
Analyze the implications of the findings: If replication were unidirectional, the replication fork would travel around the entire chromosome in one direction, taking longer to reach the terminus. However, the observed replication pattern showed that replication forks moved in opposite directions, meeting at the terminus, which is consistent with bidirectional replication.
Conclude the reasoning: The placement of the origin and terminus on opposite sides of the chromosome, combined with the observation of replication forks moving in both directions, provided strong evidence that DNA replication in E. coli is bidirectional.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Bidirectional DNA Replication
Bidirectional DNA replication refers to the process where DNA strands are synthesized in two opposite directions from a single origin of replication. In prokaryotes like E. coli, this means that replication forks move away from the origin towards the terminus, allowing for efficient and rapid duplication of the circular chromosome.
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Steps to DNA Replication
Origin and Terminus of Replication
The origin of replication is the specific location on the DNA where replication begins, while the terminus is the point where replication ends. In E. coli, the positioning of these sites on opposite sides of the circular chromosome indicates that replication occurs simultaneously in both directions, reinforcing the bidirectional nature of the process.
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Circular Chromosome Structure
E. coli possesses a circular chromosome, which allows for a unique replication mechanism. The circular structure means that once replication reaches the terminus, the two newly synthesized DNA strands can be separated efficiently, completing the replication process without the complications that linear chromosomes face, such as end replication problems.
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Related Practice
Textbook Question
Two viral genomes are sequenced, and the following percentages of nucleotides are identified:
Genome 1: A=28%, C=22%,G=28%,T=22%
Genome 2: A=22%, C=28%,G=28%,T=22%
Are the DNA molecules in each genome single-stranded or double-stranded?
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Textbook Question
Matthew Meselson and Franklin Stahl demonstrated that DNA replication is semiconservative in bacteria. Briefly outline their experiment and its results for two DNA replication cycles, and identify how the alternative models of DNA replication were excluded by the data.
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Textbook Question
Joel Huberman and Arthur Riggs used pulse–chase labeling to examine the replication of DNA in mammalian cells. Briefly describe the Huberman–Riggs experiment, and identify how the results exclude a unidirectional model of DNA replication.
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Textbook Question
Why do the genomes of eukaryotes, such as Drosophila, need to have multiple origins of replication, whereas bacterial genomes, such as that of E. coli, have only a single origin?
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Textbook Question
Bloom syndrome (OMIM 210900) is an autosomal recessive disorder caused by mutation of a DNA helicase. Among the principal symptoms of the disease are chromosome instability and a propensity to develop cancer. Explain these symptoms on the basis of the helicase mutation.
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