GeneticsLesson 2 of 3 in the course Mechanisms of Microbial Genetics

Mutation Types, DNA Damage, Repair, and Mutant Screening

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

Mutations change DNA and can alter the proteins a cell produces. This lesson introduces common DNA-sequence changes and explains how they can affect protein structure and phenotype.

A mutation is a heritable change in an organism's DNA sequence. An organism carrying a mutation is a mutant. The wild type is the phenotype most commonly observed in nature.

All flashcards

What is the wild type?
The phenotype most commonly observed in nature, used as a reference when describing mutant phenotypes.
What is a silent mutation?
A DNA-sequence change that leaves the encoded amino acid unchanged. It often has no effect on protein structure.
How does a missense mutation affect a protein?
It changes a codon so that a different amino acid is incorporated. The impact depends on the amino acid's properties and location.
What is a nonsense mutation?
A mutation that converts an amino-acid codon into a stop codon, ending translation prematurely and usually producing a shortened protein.
What causes a frameshift mutation?
An insertion or deletion of a number of nucleotides that is not a multiple of three, shifting downstream codon grouping.

Quiz questions

  1. Which statement correctly distinguishes mutagens from carcinogens?Answer: Mutagens increase mutation frequency; carcinogens cause cancer.
  2. What occurs during nucleotide excision repair of a DNA lesion?Answer: A damaged DNA segment is removed, replaced using the intact strand, and sealed.
  3. In the Ames test, what result suggests that a chemical is mutagenic?Answer: More revertant colonies grow on histidine-free medium than in the unexposed control.
  4. In replica plating, which growth pattern identifies a candidate nutrient auxotroph?Answer: A colony grows on complete medium but fails to grow on medium lacking a nutrient.
  5. How does photolyase repair a thymine dimer during photoreactivation?Answer: With visible light, it breaks the bonds linking the adjacent thymines.

Based on Microbiology by Nina Parker, Mark Schneegurt, Anh-Hue Thi Tu, Philip Lister, Brian M. Forster (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.

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