Textbook Question
Why is DNA synthesis expected to be more complex in eukaryotes than in bacteria? How is DNA synthesis similar in the two types of organisms?
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Ch. 10 - DNA Replication
Klug10th EditionEssentials of GeneticsISBN: 9780135588789
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Table of contents
- Ch. 1 - Introduction to Genetics16
- Ch. 2 - Mitosis and Meiosis28
- Ch. 3 - Mendelian Genetics37
- Ch. 4 - Modification of Mendelian Ratios53
- Ch. 5 - Sex Determination and Sex Chromosomes32
- Ch. 6 - Chromosome Mutations: Variation in Number and Arrangement37
- Ch. 7 - Linkage and Chromosome Mapping in Eukaryotes36
- Ch. 8 - Genetic Analysis and Mapping in Bacteria and Bacteriophages24
- Ch. 9 - DNA Structure and Analysis38
- Ch. 10 - DNA Replication29
- Ch. 11 - Chromosome Structure and DNA Sequence Organization22
- Ch. 12 - The Genetic Code and Transcription36
- Ch. 13 - Translation and Proteins27
- Ch. 14 - Gene Mutation, DNA Repair, and Transposition34
- Ch. 15 - Regulation of Gene Expression in Bacteria22
- Ch. 16 - Regulation of Gene Expression in Eukaryotes37
- Ch. 17 - Recombinant DNA Technology27
- Ch. 18 - Genomics, Bioinformatics, and Proteomics30
- Ch. 19 - The Genetics of Cancer21
- Ch. 20 - Quantitative Genetics and Multifactorial Traits37
- Ch. 21 - Population and Evolutionary Genetics45
Chapter 10, Problem 20c
Several temperature-sensitive mutant strains of E. coli display the following characteristics. Predict what enzyme or function is being affected by each mutation.
No initiation occurs.
Verified step by step guidance1
Step 1: Understand the biological context — the problem involves temperature-sensitive mutants of E. coli that show no initiation of a process, likely DNA replication or transcription, at the non-permissive temperature.
Step 2: Identify what 'no initiation occurs' means — in molecular biology, initiation refers to the beginning step of processes like DNA replication or transcription, where specific proteins or enzymes bind to DNA to start the process.
Step 3: Recall key enzymes involved in initiation — for DNA replication in E. coli, initiation requires the DnaA protein binding to the origin of replication (oriC) to unwind DNA and recruit other proteins; for transcription, initiation requires RNA polymerase binding to the promoter region.
Step 4: Analyze which enzyme or function is likely affected — since no initiation occurs, the mutation probably affects the protein responsible for recognizing the start site and beginning the process, such as DnaA for replication initiation or RNA polymerase for transcription initiation.
Step 5: Conclude that the mutation likely affects the initiation factor or enzyme (e.g., DnaA protein for replication initiation) that is essential for starting the process, preventing the cell from initiating DNA replication or transcription at the restrictive temperature.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Temperature-Sensitive Mutations
Temperature-sensitive mutations cause proteins to function normally at a permissive temperature but lose function at a restrictive, usually higher, temperature. These mutations help identify essential genes or enzymes by observing which cellular processes fail when the temperature shifts.
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Mutations and Phenotypes
Initiation of DNA Replication in E. coli
Initiation of DNA replication in E. coli involves the assembly of a protein complex at the origin of replication (oriC), including DnaA binding to initiate unwinding. Proper function of initiator proteins and helicases is critical to start replication; defects here prevent initiation.
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Role of Enzymes in DNA Replication Initiation
Key enzymes like DnaA (initiator), DnaB (helicase), and DnaC (helicase loader) coordinate to open the DNA helix and recruit DNA polymerase. Mutations affecting these enzymes can block initiation, causing no replication to start, which explains the phenotype of no initiation in mutant strains.
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Related Practice
Textbook Question
Several temperature-sensitive mutant strains of E. coli display the following characteristics. Predict what enzyme or function is being affected by each mutation.
Newly synthesized DNA contains many mismatched base pairs.
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Textbook Question
Several temperature-sensitive mutant strains of E. coli display the following characteristics. Predict what enzyme or function is being affected by each mutation.
Okazaki fragments accumulate, and DNA synthesis is never completed.
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Textbook Question
Several temperature-sensitive mutant strains of E. coli display the following characteristics. Predict what enzyme or function is being affected by each mutation.
Synthesis is very slow.
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Textbook Question
Several temperature-sensitive mutant strains of E. coli display the following characteristics. Predict what enzyme or function is being affected by each mutation.
Supercoiled strands remain after replication, which is never completed.
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Textbook Question
Many of the gene products involved in DNA synthesis were initially defined by studying mutant E. coli strains that could not synthesize DNA.
The dnaE gene encodes the α subunit of DNA polymerase III. What effect is expected from a mutation in this gene? How could the mutant strain be maintained?
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