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Ch. 11 - Gene Mutation, DNA Repair, and Homologous Recombination
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
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Tutti i libri di testoSanders 3rd EditionCh. 11 - Gene Mutation, DNA Repair, and Homologous RecombinationProblema 13a
Capitolo 11, Problema 13a

Answer the following questions concerning the accuracy of DNA polymerase during replication.
What general mechanism do DNA polymerases use to check the accuracy of DNA replication and identify errors during replication?

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DNA polymerases use a mechanism called 'proofreading' to ensure the accuracy of DNA replication. This involves the enzyme checking each newly added nucleotide against the template strand to confirm correct base pairing.
If an incorrect nucleotide is incorporated, the DNA polymerase detects the mismatch due to improper hydrogen bonding between the bases.
The enzyme pauses and activates its 3' to 5' exonuclease activity, which removes the incorrectly paired nucleotide from the growing DNA strand.
After the incorrect nucleotide is removed, the DNA polymerase resumes synthesis by adding the correct nucleotide to the strand.
This proofreading mechanism significantly reduces the error rate during DNA replication, ensuring high fidelity in the process.

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DNA Polymerase Function

DNA polymerases are enzymes responsible for synthesizing new DNA strands by adding nucleotides complementary to the template strand. They play a crucial role in DNA replication, ensuring that the genetic information is accurately copied. Their activity is essential for cell division and the maintenance of genetic integrity.
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Functional Genomics

Proofreading Mechanism

DNA polymerases possess a proofreading ability that allows them to identify and correct errors during DNA replication. This mechanism involves a 3' to 5' exonuclease activity, which removes incorrectly paired nucleotides. By excising these errors, DNA polymerases enhance the fidelity of DNA synthesis, reducing the mutation rate.
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Proofreading

Mismatch Repair System

In addition to the proofreading function of DNA polymerases, cells have a mismatch repair system that further ensures replication accuracy. This system detects and repairs mismatched base pairs that escape the proofreading process. It involves a series of proteins that recognize the error, excise the incorrect segment, and fill in the correct nucleotides, thus maintaining genomic stability.
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Repair Pathways
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Domanda del libro di testo

Two different mutations are identified in a haploid strain of yeast. The first prevents the synthesis of adenine by a nonsense mutation of the ade-1 gene. In this mutation, a base-pair substitution changes a tryptophan codon (UGG) to a stop codon (UGA). The second affects one of several duplicate tRNA genes. This base-pair substitution mutation changes the anticodon sequence of a tRNAᵀʳᵖ from


   3′−ACC−5′ to 3′−ACU−5′


Assuming there are no other mutations in the genome, will this double-mutant yeast strain be able to grow on minimal medium? If growth will occur, characterize the nature of growth relative to wild type.

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Domanda del libro di testo

Answer the following questions concerning the accuracy of DNA polymerase during replication.

If a DNA replication error is detected by DNA polymerase, how is it corrected?

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Domanda del libro di testo

Two different mutations are identified in a haploid strain of yeast. The first prevents the synthesis of adenine by a nonsense mutation of the ade-1 gene. In this mutation, a base-pair substitution changes a tryptophan codon (UGG) to a stop codon (UGA). The second affects one of several duplicate tRNA genes. This base-pair substitution mutation changes the anticodon sequence of a tRNAᵀʳᵖ from


   3′−ACC−5′ to 3′−ACU−5′


Do you consider the second mutation to be a forward mutation or a reversion? Why?

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Domanda del libro di testo

Answer the following questions concerning the accuracy of DNA polymerase during replication.

If a replication error escapes detection and correction, what kind of abnormality is most likely to exist at the site of the replication error?

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Domanda del libro di testo

Answer the following questions concerning the accuracy of DNA polymerase during replication.

Identify two mechanisms that can correct the kind of abnormality resulting from the circumstances identified in part (c).

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Domanda del libro di testo

What is the phenotypic effect of inserting a Ds element into the maize C gene? How do Ds and Ac produce maize kernels that are mostly yellow with purple spots?

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