DNA Repair and Associated Diseases

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Questions and Answers

What is the primary role of telomerase in cellular aging?

To increase the rate of apoptosis

To enhance DNA mutations

To replicate the entire chromosome

To prevent telomere shortening (correct)

How do mutations caused by chemical agents generally affect the cell?

They can lead to pathological conditions (correct)

They have no effect on DNA

They only cause replication errors

They always produce beneficial traits

What mechanism is responsible for repairing single-strand DNA breaks?

Homologous recombination

Base excision repair

Site-specific recombination

Non-homologous end joining (correct)

Which type of repair process is specifically designed to correct replication errors?

Mismatch repair Signup and view all the answers

Covalent modifications of DNA can lead to which of the following consequences?

Altered gene expression Signup and view all the answers

What is a characteristic feature of the base excision repair mechanism?

It involves the removal of damaged bases Signup and view all the answers

What effect do intercalating agents have on DNA?

They cause deletions or insertions Signup and view all the answers

Which of the following mutations is characterized by the addition or loss of nucleotides?

Indel mutations Signup and view all the answers

What type of mutation creates a stop codon that may result in a truncated protein?

Nonsense mutation Signup and view all the answers

What is the primary effect of indel mutations involving 1-2 base pair deletions or insertions?

Causes translation frameshift impacting all subsequent codons Signup and view all the answers

Which type of DNA repair is responsible for correcting replication errors?

Mismatch repair Signup and view all the answers

What is a recognized consequence of an abasic site in DNA?

It can lead to mutations via mutation of the bases Signup and view all the answers

What role does telomerase play in relation to aging and telomere shortening?

It helps maintain telomere length Signup and view all the answers

Which of the following agents is known for causing chromosomal breaks?

Clastogen Signup and view all the answers

What can be a beneficial effect of mutations in DNA?

Enhancing genetic variability Signup and view all the answers

Which type of agent is categorized as causing tumor initiation?

Carcinogen Signup and view all the answers

What is a characteristic of a point mutation?

Alteration of a single nucleotide Signup and view all the answers

Which type of mutation involves a purine-to-pyrimidine change?

Transversion mutation Signup and view all the answers

What is one potential effect of mutations?

Pathological consequences like diseases Signup and view all the answers

Which mechanism is responsible for repairing replication errors?

DNA mismatch repair Signup and view all the answers

Which type of chromosomal alteration involves the fusion of DNA regions from different chromosomes?

Translocation Signup and view all the answers

What is the impact of excessive DNA damage that is not properly repaired?

Development of leukemias Signup and view all the answers

What is a known cause of mutations?

Both spontaneous and induced factors Signup and view all the answers

Which of the following DNA repair processes corrects single- and double-strand breaks?

Non-homologous end joining Signup and view all the answers

Study Notes

DNA Repair

Double-strand DNA breaks can be repaired by homologous recombination or non-homologous end joining.
Mutations result from spontaneous replication errors, chemical agents, and physical agents.
Beneficial mutations can provide genetic variability and contribute to the antibody repertoire.
Pathological mutations can lead to diseases and cancer.
DNA repair mechanisms include excision repair (BER and NER), mismatch repair, and repair of single- or double-strand DNA breaks.

DNA Repair Diseases

Ataxia telangiectasia is caused by a loss-of-function mutation in the ATM gene, encoding a protein that activates DNA repair.
Werner syndrome (progeria) is caused by a mutation in a helicase/exonuclease required for telomere maintenance.
Xeroderma pigmentosum is caused by a dysfunctional DNA repair system, leading to sensitivity to UV light.

DNA Replication

The abasic sugar-phosphate unit is unstable and degrades, resulting in a single nucleotide gap in the DNA strand.
Cells can repair this type of damage quickly and precisely, making it rarely mutagenic.

Genotoxic Environmental Agents

Carcinogens cause tumorigenic transformation and the initiation of tumors.
Oncogenes support the proliferation, survival, and evolution of tumor cells.
Mutagens cause mutations, but not necessarily carcinogenic or oncogenic.
Teratogens cause developmental abnormalities in embryos and fetuses.
Clastogens cause chromosomal breaks.

Point Mutations in the Coding DNA Region

Synonomous mutations result in different codons but encode the same amino acid.
Non-synonymous mutations result in different codons that encode different amino acids, potentially affecting protein function.
Nonsense mutations create a stop codon, resulting in a shorter, truncated protein.
Readthrough mutations eliminate a stop codon, potentially extending the protein.

Indel Mutations in the Coding Region

1-2 basepair deletions or insertions (or multiples) cause a translation frameshift, leading to a garbled amino acid sequence and premature stop codon.
3 bp deletions or insertions (or multiples) remove or insert entire codons, potentially affecting amino acid sequence and protein function.

Mutations

Mutations are small alterations in the DNA sequence affecting a few nucleotides.
They occur randomly due to environmental agents or replication errors.
Mutations are sometimes necessary and natural in the body, such as in antibody-coding genes.
Mutations contribute to the variability of amino acid sequences in antibodies.

Chromosomal Alterations

Recombination, including the exchange of DNA regions with homologous sequences, can occur during meiosis and DNA repair.
Chromosomal aberrations, such as deletions, inversions, translocations, and amplifications, can affect large regions of DNA.
Chromosome copy number changes are discussed in detail in Genetics.
Chromosomal translocations can lead to oncogenes and diseases such as leukemia (e.g., Philadelphia chromosome).

Types of Mutations

Point mutations involve the alteration of a single nucleotide.
Transitions involve purine-purine or pyrimidine-pyrimidine changes (e.g., adenine to guanine, cytosine to thymine).
Transversions involve purine-pyrimidine or pyrimidine-purine changes (e.g., adenine to cytosine, thymine to guanine).
Insertions or deletions (indels) involve the insertion or deletion of one or a few nucleotides.

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Description

Explore the fascinating mechanisms of DNA repair, including homologous recombination and non-homologous end joining. This quiz covers various mutations, their impact on genetic variability and diseases like Ataxia telangiectasia and Xeroderma pigmentosum. Test your understanding of DNA replication and the significance of repair mechanisms.