BIOCHEMISTRY TOPIC 2: MUTATION AND REPAIR

Mismatch repair: Repairs a broken chromsome using genetic information from same chromosome inherited from other parent. Fixes single damaged nucleotides Fixes multiple damaged nucleotides Fixes mistakes made by DNA polymerase during DNA replication

Correct answer Fixes mistakes made by DNA polymerase during DNA replication

What is the proper order of the steps involved in excision repair? Recognize the damage, resynthesize the sequence, remove the damage, ligate the DNA backbone. Recognize the damage, remove the damage, resynthesize the sequence, ligate the DNA backbone. Recognize the damage, remove the damage, ligate the DNA backbone, resynthesize the sequence. Recognize the damage, ligate the DNA backbone, remove the damage, resynthesize the sequence.

Correct answer Recognize the damage, remove the damage, resynthesize the sequence, ligate the DNA backbone.

Homologous recombination: Fixes single damaged nucleotides Repairs a broken chromosome using genetic information from same chromosome inherited from other parent. Fixes mistakes made by DNA polymerase during DNA replication Fixes multiple damaged nucleotides

Correct answer Repairs a broken chromosome using genetic information from same chromosome inherited from other parent. Feedback Homologous refers to the pair of same chromosomes (same genes in same order, except different alleles) you inherit from each parent - for example, the two chromosome 12s in your cells, one from your mother and one from your father. Homologous recombination fixes broken chromosomes using DNA in the same position on the homologous chromosome as a template to fix the broken chromosome. Homologous recombination also shuffles DNA between the pair of chromosomes adding genetic variation.

Point mutations change the number of nucleotides in a mutant gene compared to the normal gene. Examples are missense, nonsense, and silent mutations. change the number of nucleotides in a mutant gene compared to the normal gene. Examples are insertion and deletion mutations. change a single nucleotide in a mutant gene compared to the normal gene. Examples are insertion and deletion mutations change a single nucleotide in a mutant gene compared to the normal gene. Examples are missense, nonsense, and silent mutations.

Correct answer change a single nucleotide in a mutant gene compared to the normal gene. Examples are missense, nonsense, and silent mutations.

Frameshift mutations change the number of nucleotides in a mutant gene compared to the normal gene. Examples are missense, nonsense, and silent mutations. change the number of nucleotides in a mutant gene compared to the normal gene. Examples are insertion and deletion mutations. change a single nucleotide in a mutant gene compared to the normal gene. Examples are insertion and deletion mutations change a single nucleotide in a mutant gene compared to the normal gene. Examples are missense, nonsense, and silent mutations.

Correct answer change the number of nucleotides in a mutant gene compared to the normal gene. Examples are insertion and deletion mutations. Feedback A frameshift mutation results from insertions or deletions of nucleotides into a gene. This changes the way in which mRNA codons are read in order to make a protein.

A deletion mutation is a type of point mutation. is a type of silent mutation. always results in a shorter amino acid sequence than the normal gene. might cause a nonsense mutation.

Correct answer might cause a nonsense mutation. Feedback A deletion mutation removes nucleotides from a gene and is a type of frameshift mutation. Deletion mutations always change an amino acid sequence by either removing amino acid(s) from the protein or changing the way codons are read, changing the entire amino acid sequence past the mutation. This mutation could cause the regular stop codon to be split between two adjacent codons, allowing translation to occur beyond the stop codon in the normal gene. Alternatively, the change in "reading frame" could introduce a premature stop codon.

The mutation that causes color blindness by making a shorter opsin protein could have resulted from a malfunction of __________. Primase DNA polymerase RNA polymerase Helicase

Correct answer DNA polymerase Feedback DNA polymerase could have added an erroneous nucleotide, and it's proofreading activity could have missed it. While this type of event is rare, DNA polymerase is known to make a mistake that it doesn't correct about one in one hundred million!

When the wrong nucleotide is added to a newly forming DNA strand during DNA replication Distortion of the double helix structure occurs because of uncomplimentary pairing of the nucleotides The DNA can not be repaired The cell dies Thymine dimers occur

Correct answer Distortion of the double helix structure occurs because of uncomplimentary pairing of the nucleotides Feedback A mismatch (A with C or G, T with C or G) causes a bump to form in the DNA double helix, which is recognized by proofreading enzymes and fixed by excision repair. See the Inheritance of Genes > DNA Damage and Repair > Mismatch Repair section of the Module 1 text for more information.

Base excision repair: Fixes single damaged nucleotides Repairs a broken chromosome using genetic information from same chromosome inherited from other parent. Fixes mistakes made by DNA polymerase during DNA replication Fixes multiple damaged nucleotides

Correct answer Fixes single damaged nucleotides Feedback Base excision repair replaces a single damaged nucleotide.

Which statement is true with respect to mismatch repair and nucleotide excision repair (NER)? Mismatch repair fixes thymine dimers caused by exposure to UV light, while NER fixes errors in DNA replication. Mismatch repair follows the same steps as NER. Mismatch repair uses genetic information on the opposite strand of the DNA double helix while NER uses information on the homologous chromosome. None of the above are true.

Correct answer Mismatch repair follows the same steps as NER. Feedback The basic steps of excision repair are given as bullet points at the very beginning of Lesson 1: DNA and RNA; Chapter - Inheritance of Genes; Subchapter - DNA Damage and Repair; Section - Excision Repair Corrects The Most Frequent DNA Lesions.

In sickle cell anemia, the DNA coding strand is mutated from GAG to GTG. This results in an amino acid change from Glutamic Acid to Valine. Which of the following terms correctly describes this mutation? (check all that apply) Nonsense mutation Missense mutation Silent mutation Frameshift mutation Point mutation Insertion

Correct answer Missense mutation Point mutation Feedback GAG in the normal gene is mutated to GTG in sickle cell anemia, changing the amino acid from valine (Val) to glutamate (Glu). A single nucleotide change in a codon (point mutation) that also changes one amino acid in the protein is a missense mutation.

A specific kind of mutation in the opsin gene related to color blindness causes a premature termination of the translation process. This results in a shorter opsin protein than usual. What *specific* type of mutation could have caused this? Frameshift mutation Missense mutation Point mutation Nonsense mutation

Correct answer Nonsense mutation Feedback A nonsense mutation is a kind of point mutation that changes a single base pair in a codon to a stop codon resulting in termination of the translational signal. This results in a truncated protein.

Several components of cigarette smoke, including benzopyrene, insert themselves (intercalate) into the DNA and lead to several types of mutations such as frameshift mutations, including both insertions and deletion. Which of the following repair pathways would be used to repair this type of damage? Base excision repair Mismatch Repair Nucleotide Excision Repair Homologous Recombination

Correct answer Nucleotide Excision Repair Feedback Nucleotide excision repair is used to repair deletions, insertions, and helix-distorting lesions, such as thymine dimers. To learn more about this, please visit Lesson 1: DNA and RNA; Chapter - Inheritance of Genes; Subchapter - DNA Damage and Repair; Section - Excision Repair Corrects The Most Frequent DNA Lesions.

Which of the following is NOT a step in base excision repair? Ligation to restore continuity of the DNA backbone Synthesis of an RNA primer Recognition of the damage Removal of the damage by excising part of one strand to leave a gap

Correct answer Synthesis of an RNA primer Feedback Synthesis of an RNA primer is part of DNA replication, not DNA repair.

A patient with xeroderma pigmentosum is prone to developing multiple skin cancers starting in childhood. This occurs because of a mutation in a gene that codes for enzymes that help repair DNA damage through the nucleotide excision repair (NER) pathways. How does NER differ from other repair mechanisms? In NER: Only one nucleotide is removed and DNA polymerase replaces the one abnormality The error in one strand of DNA is removed as well as several nucleotides on either side of the error. The gap that was removed is filled in by DNA polymerase The entire homologous chromosome is used to repair the double stranded DNA error The affected DNA strand and its complementary strand is discarded and a new double stranded DNA is created

Correct answer The error in one strand of DNA is removed as well as several nucleotides on either side of the error. The gap that was removed is filled in by DNA polymerase Feedback Nucleotide excision repair replaces several damaged nucleotides plus additional nucleotides and uses the DNA on the opposite strand as a template to fill in the gap.

Nonsense mutations are point mutations that change a single base pair in a codon to a stop codon that terminates translation. True False

Correct answer True Feedback A single nucleotide change in a codon (point mutation) introduces a premature stop codon into an amino acid sequence is a nonsense mutation. See Figure 1-19 in the Module 1 text for more information.

Silent mutations are point mutations that result in no change in amino acid sequence True False

Correct answer True Feedback A single nucleotide change in a codon (point mutation) which does not change the amino acid sequence is a silent mutation.

A nonsense mutation inserts or deletes nucleotides in a mutant gene compared to a normal gene. causes a double-stranded break in a chromosome. changes a codon to introduce a premature stop codon. has no effect on an amino acid sequence.

Correct answer changes a codon to introduce a premature stop codon. Feedback A single nucleotide change in a codon (point mutation ) which introduces a premature stop codon is a nonsense mutation. See Figure 1-19 in the Module 1 text for more information.

A missense mutation inserts or deletes nucleotides in a mutant gene compared to a normal gene. causes a double-stranded break in a chromosome. changes a single amino acid in a protein. has no effect on an amino acid sequence.

Correct answer changes a single amino acid in a protein. Feedback A single nucleotide change in a codon (point mutation ) which changes the amino acid sequence is a missense mutation. See Figure 1-19 in the Module 1 text for more information.

A mutation that results in a mutant gene with more nucleotides compared to the normal gene is a ________________ mutation insertion nonsense point missense

Correct answer insertion Feedback An insertion mutation adds nucleotides to a gene and is a type of frameshift mutation, which changes the way the mRNA codons are read, changing the amino acid sequence. See Figure 1-19 in the Module 1 text for more information.

Missense mutations are insertions or deletions of one or more base pairs (if the number of base pairs is not a multiple of 3) that disrupt the coding of a protein. True False

False Feedback A single nucleotide change in a codon (point mutation) which changes the amino acid sequence is a missense mutation. See Figure 1-19 in the Module 1 text for more information.

Frameshift mutations are point mutations that change a single base pair in a codon such that the codon now encodes a different amino acid. True False

False Feedback Frameshift mutations insert or delete nucleotides from a gene, changing the way mRNA codons are read, changing the amino acid sequence of a protein. See Figure 1-19 in the Module 1 text for more information.

Nucleotide excision repair: Fixes single damaged nucleotides Fixes mistakes made by DNA polymerase during DNA replication Fixes multiple damaged nucleotides Repairs a broken chromsome using genetic information from same chromosome inherited from other parent.

Feedback Nucleotide excision repair replaces several damaged nucleotides.

When comparing a normal and mutant gene sequence, how do you identify a frameshift mutation? The number of nucleotides between the normal and mutant gene sequences is identical and the amino acid sequence is different. The number of nucleotides between the normal and mutant gene sequences is identical and the amino acid sequence is identical. The number of nucleotides between the normal and mutant gene sequences is different and the amino acid sequence is identical. The number of nucleotides between the normal and mutant gene sequences is different and the amino acid sequence is different.

The number of nucleotides between the normal and mutant gene sequences is different and the amino acid sequence is different. Feedback Point mutations (single nucleotide change in a codon) do not increase or decrease the number of nucleotides in a gene, and they might (missense and nonsense mutations) or might not (silent mutations) change the amino acid sequence of the protein. Frameshift mutations occur when nucleotides are added or deleted, changing the way mRNA is read to make a protein. See Figure 1-19 in the Module 1 text for more information.

Which of the following DNA repair mechanisms can fix the damage done by UV radiation in the form of thymine dimers? base excision repair nucleotide excision repair homologous recombination mismatch repair

nucleotide excision repair Feedback Nucleotide excision repair replaces several damaged nucleotides (such as thymine dimers) plus additional nucleotides and uses the DNA on the opposite strand as a template to fill in the gap. See Figure 1-22 in the Module 1 text for more information.

A mutation that changes the sequence of a codon but not the amino acid sequence describes a frameshift mutation. missense mutation. nonsense mutation. silent mutation.

silent mutation Feedback A single nucleotide change in a codon (point mutation ) which does not change the amino acid sequence is a silent mutation.