Mutations and DNA Repair Quiz

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Questions and Answers

What do base analogs affect during the DNA process?

They have no effect on DNA.

They have an effect only when incorporated during DNA replication. (correct)

They only affect DNA after replication.

They are effective only during RNA transcription.

What alteration does intercalative dye induce in DNA?

It deaminates adenine and cytosine.

It promotes DNA replication.

It causes base pair deletion or insertion. (correct)

It stabilizes the double helix structure.

What type of mutations allow protein B to bind to the mutant protein A?

Missense mutations

Silent mutations

Frame shift mutations

Nonsense mutations (correct)

Which statement regarding ionizing radiation is TRUE?

It can penetrate through glass and other materials. Signup and view all the answers

What role does the altered tRNA play in suppressing mutations?

It pairs with stop codons Signup and view all the answers

What is the process of reversion in genetics?

Regaining the wild type phenotype through back mutation. Signup and view all the answers

What is the main purpose of the Ames test?

To identify potential mutagens and carcinogens Signup and view all the answers

Which mutagen specifically deaminates adenine and cytosine?

Nitrous acid. Signup and view all the answers

In the Ames test, which type of mutants are primarily used?

His- mutants of Salmonella typhimurium Signup and view all the answers

What role do free radicals play in the effects of ionizing radiation?

They inactivate macromolecules including DNA. Signup and view all the answers

What is the typical mutation rate for a bacterium per base pair?

10–7 to 10–11 Signup and view all the answers

What is a pseudoreversion?

A second-site mutation that suppresses the original mutation. Signup and view all the answers

What is a key modification in the Ames test protocol?

Adding liver enzyme preparations Signup and view all the answers

Which of the following best describes spontaneous reversion?

A natural restoration of the original phenotype Signup and view all the answers

What distinguishes an auxotroph from a prototroph?

An auxotroph has a nutritional requirement for growth. Signup and view all the answers

What happens during the formation of pyrimidine primers?

They increase misreading probability during replication. Signup and view all the answers

Which DNA repair mechanism involves correcting mispaired nucleotides?

Mismatch repair Signup and view all the answers

Which type of mutation can lead to the creation of a stop codon?

Nonsense mutation Signup and view all the answers

What is the main consequence of a frameshift mutation?

It alters the three-dimensional structure of the protein. Signup and view all the answers

What kind of enzymes are involved in modifying carcinogenic substances into their active forms within the liver?

Mixed-function oxygenases Signup and view all the answers

Which type of mutation involves the movement of a large section of chromosomal DNA?

Translocation Signup and view all the answers

How can point mutations potentially be reverted?

Through subsequent mutations. Signup and view all the answers

What occurs during a missense mutation?

The amino acid sequence changes, possibly impacting protein activity. Signup and view all the answers

What is primarily responsible for the high mutation rate in RNA genomes compared to DNA genomes?

Differences in polymerase fidelity. Signup and view all the answers

What type of mutation involves a single changed base pair?

Point mutation Signup and view all the answers

Which of the following is an example of a mutagen?

Oxygen radicals Signup and view all the answers

What characteristic defines a conditional mutation?

Mutation only expressed under specific conditions Signup and view all the answers

Which type of mutation leads to a nonfunctional or truncated polypeptide?

Nonsense mutation Signup and view all the answers

How is the phenotype represented in nomenclature?

In upper case letters Signup and view all the answers

The majority of spontaneous mutations occur due to which of the following?

Errors during DNA replication Signup and view all the answers

Which of the following describes a missense mutation?

Change that results in an entirely different amino acid Signup and view all the answers

What is the term for the process of producing a mutant?

Mutagenesis Signup and view all the answers

What generally results from the insertion of a transposable element within a gene?

Loss of function Signup and view all the answers

Which of the following describes a same-site revertant?

The mutation restoring activity occurs at the same site Signup and view all the answers

Which type of mutation is typically considered nonrevertable?

Large scale deletions Signup and view all the answers

What is the primary distinction between chemical mutagens and physical mutagens?

Chemical mutagens involve base-pair substitutions Signup and view all the answers

Which enzyme is specifically involved in repairing pyrimidine dimers through direct reversal?

Photolyase Signup and view all the answers

Alkylating agents are known to cause which of the following effects?

Induction of faulty base pairing Signup and view all the answers

What happens to DNA replication when polymerase III encounters a thymine dimer?

Replication is stalled at the site of the dimer. Signup and view all the answers

What characterizes spontaneous mutagenesis?

Occurs due to natural processes Signup and view all the answers

What is the consequence of a mutation in any of the genes involved in the excision-repair process for patients with Xeroderma pigmentosum?

Sensitivity to sunlight and risk of skin cancer. Signup and view all the answers

What is the role of nucleotide base analogs in mutagenesis?

They mimic normal bases during DNA replication Signup and view all the answers

Which type of mutagen is characterized by being able to induce changes even in nonreplicating DNA?

Alkylating agents Signup and view all the answers

Which mechanism does NOT directly involve photolyase for repairing DNA?

Excision repair Signup and view all the answers

In the context of DNA repair, what role do AP endonucleases play?

They repair apurinic sites. Signup and view all the answers

What is a common characteristic of Cockayne's syndrome in relation to DNA repair?

Increased sensitivity to UV light and developmental abnormalities. Signup and view all the answers

Which of the following statements about the SOS response is true?

It can induce cell death if damage is unrepaired. Signup and view all the answers

What is the function of glycosylases in the DNA repair process?

To remove specific damaged bases. Signup and view all the answers

Study Notes

Mutations, Mutagenesis and DNA Repair

Mutant: An organism or gene that differs from the wild type.
Examples of mutants: His- yeast, white-eyed Drosophila, Lac- in E. coli (unable to metabolize lactose).
Mutation: Any heritable change in the DNA base sequence.
Mutagen: A physical or chemical agent causing mutations.

Types of Mutagenesis

Point mutation: A change in a single base pair.
- Base substitution: One base is replaced by another.
  - Transition: A purine replaces a purine or a pyrimidine replaces a pyrimidine.
  - Transversion: A purine replaces a pyrimidine or vice versa.
- Base deletion/addition: One or more bases are removed or added to the DNA sequence.
Multiple mutation: Two to three base pairs are changed.

Mutagenesis

Spontaneous mutagenesis: Occurs naturally.
- Natural radiation: Example is part of the process.
Induced mutagenesis: Caused by a mutagen.
- Oxygen radicals: Chemically modify DNA. Example is oxidation of guanine to 8-hydroxyguanine.
- Errors in base pairing: During DNA replication.

Types of Mutations

Silent (neutral) mutation: Little to no change in amino acid sequence or protein function.
Missense (nonsense) mutation: Leads to the production of a non-functional or truncated polypeptide.

Conditional Mutations

Temperature-sensitive (ts mutant): The protein is active at one temperature but inactive at another.
Termination or nonsense mutation: Results in a stop codon.

Phenotype and Genotype Notation

Phenotype (e.g., His+, Lac+) is capitalized, while genotype (e.g., his+, lac+) is lowercase.
(+) means able to perform a function, (-) means unable.
Amp-r means ampicillin resistant, Amp-s means sensitive. Genotypes are amp-r and amp-s.

Biochemical Basis of Mutants

Destruction of three-dimensional protein structure.
- Interaction between positively charged amino acid (lysine) and negatively charged amino acid (glutamic acid) is disrupted by substitution.
- Hydrophobic structure disruption by substitution.
- Mutation in the active site.

Mutation Rates

Different mutation types occur at different rates.
Typical bacteria have mutation rates of 10⁻⁷ to 10⁻¹¹ per base pair.

Mutations in RNA Genomes

RNA genomes accumulate mutations at higher frequencies than DNA genomes, even though the error rate of the polymerases is similar.

Isolation of Mutant: Screening Versus Selection

Auxotroph: A mutant requiring a nutrient for growth.
Prototroph: The parent form from which the auxotroph derived.
E-coli with a His⁻ phenotype is a histidine auxotroph.

Replica Plating

A technique to identify mutants that won't grow in specific media.

Types of Chemical Mutagens

Nucleotide base analogs: Mimic normal bases, causing errors in base pairing.
Alkylating agents: Add alkyl groups to DNA, causing base substitution.
Intercalating agents: Insert between DNA base pairs, causing frameshift mutations.
Nitrous acid: Deaminates A and C.
Hydroxylamine: Reacts with C.

DNA Repair Mechanisms

Proofreading activity of polymerase enzymes: Correcting errors during DNA replication.
Mismatch repair: Repairing mistakes in base pairing.
DNA repair of depurination: Removing missing purines.
DNA repair of deamination: Removing missing cyanides.
DNA repair by direct reversal: Repairing damaged bases.
DNA repair by excision repair: Removing bulky lesions from DNA.
Recombinational repair: Repairing DNA with gaps.
SOS response: A complex cellular mechanism that copes with DNA damage.

Ames Test

Screening for mutagens/carcinogens.
Organisms are used as a biological marker.
Liver preparations introduced to the test.
Used to help understand potential cancer connections in different substances.

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Description

Test your knowledge on mutations, mutagenesis, and DNA repair mechanisms. This quiz covers various types of mutations, their causes, and examples of mutants. Gain insights into spontaneous and induced mutagenesis through engaging questions.