Biology Chapter 10: DNA Mutability and Repair

The low mutation rate is maintained through error-checking during DNA replication and repair mechanisms. This rate is critical for ensuring the accurate transmission of genetic information across generations.

Transitions involve the substitution of a pyrimidine for a pyrimidine or a purine for a purine, while transversions involve the substitution of a pyrimidine for a purine or vice versa.

Transposons, or 'jumping genes,' can insert themselves into various locations within the genome, causing mutations or disrupting gene function. Their activity can lead to genetic instability and variability within populations.

<p>Cells distinguish the parental strand from the daughter strand using specific markers such as DNA methylation patterns that are characteristic of the original template DNA.</p> Signup and view all the answers

<p>A balance between mutation and repair fosters genetic diversity essential for natural selection and adaptation, driving the formation of new species while maintaining genomic integrity.</p> Signup and view all the answers

<p>They cause drastic changes in DNA.</p> Signup and view all the answers

<p>'Hot spots' are areas where mutations occur at a high frequency, such as DNA microsatellites.</p> Signup and view all the answers

<p>It helps to correct misincorporated nucleotides during DNA synthesis.</p> Signup and view all the answers

<p>It rapidly scans for mismatches and corrects them accurately on the newly synthesized strand.</p> Signup and view all the answers

<p>MutS detects mismatches in the DNA.</p> Signup and view all the answers

<p>Dam methylase adds a methyl group to adenine residues in the parental strands.</p> Signup and view all the answers

<p>MutH binds to hemimethylated sites and nicks the unmethylated strand.</p> Signup and view all the answers

<p>Rapid scanning for mismatches and accurate correction of the newly synthesized strand.</p> Signup and view all the answers

<p>Thymine is generated from the deamination of cytosine.</p> Signup and view all the answers

<p>Alkylation can generate methylguanine, which mispairs with thymine.</p> Signup and view all the answers

<p>Reactive oxygen species oxidize guanine, resulting in oxoguanine.</p> Signup and view all the answers

<p>Ultraviolet radiation causes the formation of thymine dimers.</p> Signup and view all the answers

<p>They primarily cause double-strand breaks in the DNA.</p> Signup and view all the answers

<p>Base analogs are incorporated into DNA and can lead to inaccurate base-pairing.</p> Signup and view all the answers

<p>Intercalating agents slip between DNA bases, causing insertions or deletions.</p> Signup and view all the answers

<p>Bleomycin causes breaks in DNA, targeting rapidly dividing cells.</p> Signup and view all the answers

<p>Thymine dimers can block DNA replication and transcription.</p> Signup and view all the answers

<p>Deamination of cytosine results in a conversion from C:G to T:A, creating a transition mutation.</p> Signup and view all the answers

<p>Photolyase uses energy from light to break the covalent bonds linking pyrimidines in thymine dimers.</p> Signup and view all the answers

<p>Glycosylases hydrolyze the glycosidic bond of damaged bases, allowing for their removal.</p> Signup and view all the answers

<p>Nucleotide excision repair cleaves DNA on either side of a lesion, while base excision repair targets individual damaged bases.</p> Signup and view all the answers

<p>Translesion Polymerase synthesizes DNA across the site of damage, allowing replication to continue despite DNA lesions.</p> Signup and view all the answers

<p>If not removed, the oxoG:A pair may form, potentially causing a mispairing during replication.</p> Signup and view all the answers

<p>Methyltransferase removes the methyl group from methylguanine, transferring it to its own cysteine residue.</p> Signup and view all the answers

<p>They degrade DNA in the 5' to 3' direction, specifically removing mismatched DNA cleaved on the 5' side of the mismatch.</p> Signup and view all the answers

<p>Exonuclease I degrades DNA in the 3' to 5' direction and is used when the nick is on the 3' side of the mismatch.</p> Signup and view all the answers

<p>MSH proteins recruit mismatch repair proteins to both the lagging and leading strands to facilitate the repair process.</p> Signup and view all the answers

<p>Mutations in MutS and MutL can lead to an increased risk of colon cancer.</p> Signup and view all the answers

<p>DNA damage can occur due to spontaneous hydrolysis, environmental factors like radiation, and chemical mutagens.</p> Signup and view all the answers

<p>Cytosine deamination generates uracil, an unnatural base in DNA, which can disrupt pairing and lead to mutations.</p> Signup and view all the answers

<p>Thymine helps in distinguishing between natural and damaged bases, reducing the occurrence of mutations.</p> Signup and view all the answers

<p>The Ames Test is used to identify potential mutagens by measuring their effect on mutation frequency in bacteria.</p> Signup and view all the answers

<p>UvrA and UvrB scan the DNA for lesions.</p> Signup and view all the answers

<p>UvrC creates two incisions, one 4-5 nucleotides 3’ and another 8 nucleotides 5’ to the lesion.</p> Signup and view all the answers

<p>RNA polymerase scans for DNA damage and recruits nucleotide excision repair proteins when it encounters lesions.</p> Signup and view all the answers

<p>XPC detects distortions in the DNA helix.</p> Signup and view all the answers

<p>TFIIH unwinds the DNA template and includes helicase activity for lesion melting.</p> Signup and view all the answers

<p>NHEJ processes broken ends and joins them, but sequence information is lost, making it mutagenic.</p> Signup and view all the answers

<p>XPA forms a bubble by helicase activity, and ERCC1-XPF cuts DNA 5’ to the lesion.</p> Signup and view all the answers

<p>DSBs can block replication and cause cell death, repaired by non-homologous end joining or homologous recombination.</p> Signup and view all the answers

Permanent changes in DNA sequence, affecting phenotype and driving evolution.

Inaccuracies during DNA replication, a major source of mutations.

A change in a single nucleotide in a DNA sequence.

A point mutation where a purine replaces a purine or a pyrimidine replaces a pyrimidine.

A point mutation where a purine replaces a pyrimidine or vice versa.

The frequency at which mutations occur naturally during DNA replication.

Short, repeated DNA sequences (e.g., CA repeats) that are prone to mutation.

A system that corrects errors in DNA replication that were missed by the proofreading step.

A built-in mechanism in DNA replication machinery that checks for and corrects errors.

A protein that detects mismatched nucleotides in DNA.

A protein that assists in mismatch repair by working with MutS and MutH

Newly synthesized DNA strand that is not yet methylated, while the template (parental) strand is.

An enzyme that adds a methyl group to adenine residues in DNA, crucial for mismatch repair.

DNA damage can block replication and transcription or lead to mutations.

Two adjacent thymine bases covalently linked, blocking DNA replication and transcription.

Cytosine loses its amino group, converting it to uracil, which pairs with adenine, causing a C:G to T:A mutation.

A DNA repair mechanism that removes damaged nucleotides by cutting out the damaged section and replacing it with the correct sequence.

Repairing double-strand breaks in DNA by using homologous recombination to copy an undamaged section of DNA.

A specialized DNA polymerase that can bypass damaged DNA regions, allowing replication to continue.

This repair process uses light energy to break the covalent bonds linking pyrimidines in a thymine dimer.

An enzyme that removes a methyl group from methylguanine, a common DNA damage, by transferring it to one of its own cysteine residues.

A modified form of cytosine found in higher eukaryotes. It's involved in silencing genes and can deaminate to thymine, causing a C to T mutation.

When methyl or ethyl groups attach to DNA bases, they can disrupt base pairing. For example, methylguanine pairs with thymine instead of cytosine, introducing an error.

Reactive oxygen species (ROS) can oxidize guanine, creating oxoguanine. This modified base pairs with both adenine and cytosine, leading to errors in replication.

Ultraviolet radiation causes thymine dimers, where two adjacent thymines fuse together. This distortion blocks DNA replication.

Gamma radiation and X-rays can break both strands of DNA, leading to severe damage. This can be lethal to the cell.

Chemicals that resemble normal DNA bases are incorporated into DNA during replication. They pair inaccurately, causing mutations. Example: 5-bromouracil mimics thymine.

Molecules that slip between DNA base pairs, causing insertions or deletions of nucleotides. This disrupts the reading frame and leads to errors in protein synthesis.

A DNA repair mechanism that removes damaged or altered nucleotides from a DNA strand by excising a short segment of DNA containing the lesion and replacing it with a new, correctly synthesized segment.

A set of four proteins (UvrA, UvrB, UvrC, and UvrD) that are involved in nucleotide excision repair in bacteria like E. coli.

A key protein in eukaryotic NER that detects distortions or abnormalities in the DNA helix, signaling the need for repair.

A multi-protein complex important in both gene transcription and transcription-coupled repair (TCR). It unwinds the DNA template during both processes.

A specialized type of NER specifically for removing damage from actively transcribed DNA. RNA polymerase, during transcription, detects damage and recruits repair proteins.

A DNA repair mechanism used for repairing double-strand breaks (DSB) in DNA. It joins broken ends together directly, but may result in loss of sequence information. Although it is prone to mistakes, it is crucial for protecting cells from DSBs.

A severe DNA damage where both strands of the DNA molecule are broken. If left unrepaired, DSBs can lead to serious consequences like chromosome loss and cell death.

Both mechanisms repair DNA damage, but use different strategies. Excision repair removes and replaces damaged DNA using the undamaged strand as a template. Recombination repair uses undamaged DNA as a template to replace the damaged segment.

These exonucleases degrade DNA in a 5' to 3' direction, removing single-stranded DNA between a nick and a mismatch when the nick is on the 5' side of the mismatch.

This exonuclease degrades DNA in a 3' to 5' direction, removing single-stranded DNA between a nick and a mismatch when the nick is on the 3' side of the mismatch.

Eukaryotic proteins homologous to MutL, working with MSH to initiate mismatch repair.

The removal of an amino group (-NH2) from a base in DNA, leading to the formation of a different base. Cytosine deamination generates uracil.

An unnatural base in DNA, formed by cytosine deamination. It results in the substitution of a G-C pair with an A-U pair.

A widely used method to identify potential mutagens, which are chemical agents that increase mutation frequency.

Unnatural bases formed by deamination of adenine and guanine, respectively. Hypoxanthine pairs with cytosine, while xanthine pairs with cytosine with weaker bonding.