Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

8. DNA Replication

Overview of DNA Replication

Genetics

8. DNA Replication

Overview of DNA Replication

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2:31 minutes

Problem 20c

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.
No initiation occurs.

Verified step by step guidance

Identify the process of initiation in E. coli. In the context of genetics, initiation refers to the beginning of DNA replication, transcription, or translation. Since the problem involves temperature-sensitive mutants, focus on the enzymes or proteins involved in these processes.

Consider the enzymes or proteins required for initiation in DNA replication. In E. coli, the enzyme DnaA is responsible for recognizing the origin of replication (oriC) and initiating the unwinding of DNA. A mutation affecting DnaA could prevent initiation of DNA replication.

Examine the initiation of transcription. RNA polymerase, specifically its sigma factor (σ), is essential for recognizing promoter sequences and initiating transcription. A mutation affecting the sigma factor could prevent transcription initiation.

Analyze the initiation of translation. The small ribosomal subunit, along with initiation factors (IF1, IF2, and IF3), is required to assemble the ribosome at the start codon of mRNA. A mutation affecting one of these initiation factors could prevent translation initiation.

Determine which initiation process is most likely affected based on additional experimental data or context provided. For example, if the mutant strain fails to grow due to lack of protein synthesis, the issue may lie in translation initiation. If DNA replication is halted, the mutation likely affects DnaA.

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Key Concepts

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

Gene Expression Regulation

Gene expression regulation involves the processes that control the timing and amount of gene product (RNA or protein) produced in a cell. In bacteria like E. coli, this regulation is crucial for responding to environmental changes, including temperature. Mutations affecting initiation can disrupt the transcription or translation processes, leading to a failure in producing necessary proteins.

Transcription Initiation

Transcription initiation is the first step in gene expression, where RNA polymerase binds to the promoter region of a gene to begin synthesizing RNA. In E. coli, this process requires specific proteins and factors, such as sigma factors, to recognize the promoter. Mutations that affect these components can prevent the initiation of transcription, resulting in no RNA synthesis.

Temperature-Sensitive Mutations

Temperature-sensitive mutations are genetic alterations that result in a protein functioning normally at one temperature but becoming inactive or dysfunctional at another. In the context of E. coli, these mutations can affect enzymes or proteins involved in critical cellular processes, such as initiation of transcription or translation, leading to observable phenotypic changes at non-permissive temperatures.

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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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Textbook Question

Suppose that E. coli synthesizes DNA at a rate of 100,000 nucleotides per minute and takes 40 minutes to replicate its chromosome.

(a) How many base pairs are present in the entire E. coli chromosome?

(b) What is the physical length of the chromosome in its helical configuration—that is, what is the circumference of the chromosome if it were opened into a circle?

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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

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.

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.

Newly synthesized DNA contains many mismatched base pairs.

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Textbook Question

DNA supercoiling, which occurs when coiling tension is generated ahead of the replication fork, is relieved by DNA gyrase. Supercoiling may also be involved in transcription regulation. Researchers discovered that enhancers operating over a long distance (2500 bp) are dependent on DNA supercoiling, while enhancers operating over shorter distances (110 bp) are not so dependent [Liu et al. (2001). Proc. Natl. Acad. Sci. USA 98:14,883–14,888]. Using a diagram, suggest a way in which supercoiling may positively influence enhancer activity over long distances.

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Textbook Question

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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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.

Key Concepts

Gene Expression Regulation

Transcription Initiation

Temperature-Sensitive Mutations

Watch next

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.