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Questions and Answers
What type of mutation results in the protein being truncated?
What type of mutation results in the protein being truncated?
Which type of mutation occurs when a purine is replaced by a pyrimidine?
Which type of mutation occurs when a purine is replaced by a pyrimidine?
What can somatic cell mutations potentially cause?
What can somatic cell mutations potentially cause?
Which category of mutations can affect transcriptional regulation?
Which category of mutations can affect transcriptional regulation?
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How does a missense mutation affect protein structure?
How does a missense mutation affect protein structure?
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What is the role of DNA-damaging agents in cancer therapy?
What is the role of DNA-damaging agents in cancer therapy?
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What is the main consequence of a silent mutation?
What is the main consequence of a silent mutation?
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Which type of mutation affects adult size and shape in progeny?
Which type of mutation affects adult size and shape in progeny?
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What is codon bias?
What is codon bias?
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What is the primary method by which 99% of spontaneous replication errors are corrected?
What is the primary method by which 99% of spontaneous replication errors are corrected?
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Spontaneous mutations can arise during which of the following processes?
Spontaneous mutations can arise during which of the following processes?
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Why is mismatch repair important?
Why is mismatch repair important?
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How often does DNA polymerase typically make replication errors?
How often does DNA polymerase typically make replication errors?
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What is a potential side effect of chemotherapy or radiotherapy?
What is a potential side effect of chemotherapy or radiotherapy?
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Which of the following is NOT a characteristic of cancer cells?
Which of the following is NOT a characteristic of cancer cells?
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What role does proofreading activity play in DNA replication?
What role does proofreading activity play in DNA replication?
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What can cause DNA damage leading to mismatches during DNA synthesis?
What can cause DNA damage leading to mismatches during DNA synthesis?
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What can DNA slippage lead to?
What can DNA slippage lead to?
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Which term describes a mutation caused by external factors?
Which term describes a mutation caused by external factors?
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What method is commonly used to repair mismatches in DNA?
What method is commonly used to repair mismatches in DNA?
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What typically accounts for most replication errors?
What typically accounts for most replication errors?
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Which of the following statements is false regarding silent mutations?
Which of the following statements is false regarding silent mutations?
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What can cause a wrong base to be inserted during DNA replication?
What can cause a wrong base to be inserted during DNA replication?
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What sequence is used by CRISPR to identify the target DNA for cutting?
What sequence is used by CRISPR to identify the target DNA for cutting?
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Which components are essential for Cas9 to successfully cut DNA?
Which components are essential for Cas9 to successfully cut DNA?
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What is the role of the guide RNA in the CRISPR/Cas9 system?
What is the role of the guide RNA in the CRISPR/Cas9 system?
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What is a significant characteristic of the CRISPR system in bacteria?
What is a significant characteristic of the CRISPR system in bacteria?
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In genome editing using CRISPR/Cas9, what is a potential outcome for the target organism?
In genome editing using CRISPR/Cas9, what is a potential outcome for the target organism?
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What is one way that CRISPR can be introduced into the target organism?
What is one way that CRISPR can be introduced into the target organism?
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What is the role of trancrRNA in the CRISPR/Cas9 system?
What is the role of trancrRNA in the CRISPR/Cas9 system?
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What type of organisms have been cited as editable using the CRISPR/Cas9 technique?
What type of organisms have been cited as editable using the CRISPR/Cas9 technique?
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What is the primary role of MutS in the mismatch repair process?
What is the primary role of MutS in the mismatch repair process?
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Which statement accurately describes the actions of MutH in mismatch repair?
Which statement accurately describes the actions of MutH in mismatch repair?
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Which gene defects are commonly associated with hereditary non-polyposis colon cancer?
Which gene defects are commonly associated with hereditary non-polyposis colon cancer?
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In which organism's DNA repair system are MSH and MLH genes first studied?
In which organism's DNA repair system are MSH and MLH genes first studied?
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What is the first step in base excision repair?
What is the first step in base excision repair?
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What type of mutations are associated with hereditary non-polyposis colon cancer?
What type of mutations are associated with hereditary non-polyposis colon cancer?
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What enzyme is known to be missing in eukaryotes for incision during mismatch repair?
What enzyme is known to be missing in eukaryotes for incision during mismatch repair?
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Which repair pathway involves excision of a damaged region and using complementary DNA as a template?
Which repair pathway involves excision of a damaged region and using complementary DNA as a template?
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What type of DNA damage is primarily repaired by nucleotide excision repair?
What type of DNA damage is primarily repaired by nucleotide excision repair?
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Which proteins are part of the multienzyme complex in bacteria involved in nucleotide excision repair?
Which proteins are part of the multienzyme complex in bacteria involved in nucleotide excision repair?
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What is a major consequence of uncorrected DNA double-strand breaks?
What is a major consequence of uncorrected DNA double-strand breaks?
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What is the role of DNA helicase in nucleotide excision repair?
What is the role of DNA helicase in nucleotide excision repair?
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Xeroderma pigmentosum is associated with a defect in which DNA repair mechanism?
Xeroderma pigmentosum is associated with a defect in which DNA repair mechanism?
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What is a primary method of repair for DNA double-strand breaks?
What is a primary method of repair for DNA double-strand breaks?
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What is the initial step in the homologous recombination repair process?
What is the initial step in the homologous recombination repair process?
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What is a critical function of ligase in DNA repair mechanisms?
What is a critical function of ligase in DNA repair mechanisms?
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Study Notes
DNA Mutation and Repair
- Learning Outcomes:
- Explain DNA structure, organization, DNA replication mechanisms, and repair mechanisms.
- Demonstrate understanding of various modern molecular biology techniques.
- Peppered Moth Example:
- A study identified the gene responsible for the peppered moth adapting to pollution by turning black.
- This adaptation occurred due to a genetic mutation.
- Types of Mutations:
- Mutations alter DNA sequence.
- Point mutation: A single nucleotide change.
- Insertion: Addition of one or more nucleotides.
- Deletion: Removal of one or more nucleotides.
- Transversion mutation: A purine is replaced by a pyrimidine, or vice-versa.
- Transition mutation: A purine is replaced by a purine, or a pyrimidine is replaced by a pyrimidine.
- Location of Mutations:
- Germ cells (sperm/eggs): Cause heritable defects.
- Somatic cells (non-reproductive cells): Can cause diseases like cancer.
- Cells in developing embryos: Can lead to developmental defects.
- Effects of Mutations in Genes:
- Coding genes: Affect protein expression or structure.
- Non-coding RNA (e.g., rRNA, tRNA): Affect translation, transcription, or splicing.
- Non-transcribed regions (e.g., promoters, enhancers): Affect transcriptional regulation.
- Mutations can occur anywhere in the genome.
- Effects on Proteins:
- Nonsense mutation: Truncates the protein.
- Missense mutation: Changes a single amino acid.
- Frameshift mutation: Changes the reading frame, altering subsequent amino acids.
- Silent mutation: No effect on the amino acid sequence.
- Silent Mutations:
- No effect on amino acid sequences.
- Can affect transcription or translation.
- Multiple codons may code for a single amino acid.
- Some organisms prefer particular codons for an amino acid (codon bias).
- DNA Mutations:
- Spontaneous (occur during normal cellular processes):
- Errors during DNA replication.
- Modifications of DNA bases.
- Replication errors (wrong bases, skipping bases).
- Spontaneous (occur during normal cellular processes):
- Replication Errors:
- Most replication errors are corrected by proofreading activity of DNA polymerase (3' to 5' exonuclease activity).
- Errors are relatively rare (1 in 105 to 106 base pairs).
- Replication slippage:
- Can potentially result in repetitive sequences, as errors accumulate (e.g., in the Huntingtin gene, associated with Huntington's disease).
- Induced Mutations:
- Caused by exogenous agents (mutagens).
- Discuss examples of mutagens in pairs.
- Caused by exogenous agents (mutagens).
- Use of Mutations in Research:
- Mutagens (e.g., EMS, ENU) can be used to create targeted mutations.
- This allows mutations in genes to be linked to phenotypes and help identify genes involved in diseases.
- Use of Mutations in Therapy:
- DNA-damaging agents (e.g., chemo/radiotherapy) are more effective against rapidly dividing cancer cells.
- DNA repair:
- Many repair systems exist to maintain genetic stability following DNA damage.
- Repair of Mismatches:
- Mismatches arise during DNA synthesis & other ways
- ~99% of replication errors repaired by DNA polymerase's proofreading (3' to 5' exonuclease activity)
- Mismatch repair (in E. coli);
- MutS recognizes mismatch.
- MutL activates MutH.
- MutH creates a nick nearby the methylated sequence.
- Mismatch Repair in Humans:
- Similar process in humans.
- Uses MutS homologs (MSH1, MSH2) and MutL homologs (MLH1).
- Mismatch Repair and Colon Cancer:
- A defect of Mismatch repair enzymes is involved in hereditary non-polyposis colon cancer (HNPCC, aka Lynch syndrome).
- Excision Repair:
- Base excision repair: Removes damaged bases.
- Nucleotide excision repair: Removes damaged segments of DNA.
- Double-Strand Breaks:
- Difficult to repair.
- Homologous Recombination:
- Involves pairing with a homologous DNA sequence.
- More complex than other repair mechanisms.
- Non-homologous End Joining (NHEJ):
- Repairs double-strand DNA breaks.
- CRISPR/Cas9 system
- Bacterial defense system creating 'immunological memory'
- Bacteria cuts foreign DNA.
- Uses Guide RNA to target a specific DNA sequence and cuts the targeted DNA
- Used in genome editing.
- Genome Editing Using CRISPR/Cas9:
- Used to introduce targeted mutations.
- What Next?
- Further research to explore the potential in therapeutic applications and ethical considerations.
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Description
Explore the mechanisms of DNA structure, replication, and repair in this quiz. Understand various types of mutations with real-world examples like the peppered moth. Test your knowledge on the implications of mutations in germ and somatic cells.
