Chapter 12 Flashcards
DNA mutation
An inheritable change in DNA sequence
The change of a single base pair is known as
point mutation
where one purine-pyrimidine base pair is exchanged for another purine-pyrimidine pair (C≡G becomes T=A or vice versa)
transition mutation
where a purine-pyrimidine base pair is replaced with a pyrimidine-purine base
pair, or vice versa (ex: C≡G becomes either G≡C or A=T).
transversion mutation
does not change any amino acid in the protein (due to the redundancy of codons).
silent mutation
a point mutation generating a change in a single amino acid. [example: glutamate
(GAA) to glutamine (CAA) exchange]
missense mutation
induces instead of an amino acid codon, a stop codon. This generates a truncated
protein.
nonsense mutation
Mutations are incorporated in how many steps
two-step process
A mutation caused by insertion of one or more extra bases between successive bases in DNA.
insertion mutation
A mutation resulting from the deletion of one or more nucleotides from a gene or chromosome. Compare insertion mutation.
deletion mutation
A collective term for insertion and deletion mutations
indels
A mutation caused by insertion or deletion of one or more paired nucleotides, changing the reading frame of codons during protein synthesis; the polypeptide product has an altered amino acid sequence beginning at the mutated codon.
frameshift mutation
The duplication of a large tract of DNA, leading to an increased dosage of genes in the affected area.
duplication mutation
A mutation that results from the inversion of a large segment of DNA in a chromosome.
inversion mutation
A mutation that results from the exchange of large segments of DNA between nonhomologous chromosomes.
translocation mutation
causes of indels
- abberant recombination
- template slippage by dna polymerase
The enzymatic removal of amino groups from biomolecules such as amino acids or nucleotides
deamination
A position in an intact DNA backbone that is missing the base. Also called an AP (apurinic or apyrimidinic) site.
abasic site
A mutation in a gene that reverses a previous mutation. Also called a back mutation. A true reversion restores the original gene sequence; a second-site reversion restores the functionality (phenotype)
reversion mutation
the addition of an alkyl group to atoms in the
nucleotide bases or to the phosphodiester bond
alkylation
A covalently joined dimer of two adjacent pyrimidine residues in DNA, induced by absorption of UV light; most commonly derived from two adjacent thymines
pyrimidine dimer
a cross-linking agent. It alkylates DNA at
the N7 position of purines
cisplatin
effects of cisplatin
can form either intra-strand or inter-strand cross-links that are hard to repair and usually stop the
replication fork, ultimately leading to cell death.
a complex biomolecule isolated from a bacterium.
bleomycin
effects of bleomycin
binds an atom of iron and activates molecular
oxygen to form hydroxyl radicals that damage
DNA. It typically does so by binding to DNA.
A structure formed by the condensation of two double-bonded C5=C6 atoms on adjacent pyrimidine bases in DNA.
cyclobutane ring
can be used to damage dna such as uv light
ionizing radiation
An enzymatic system for repairing base mismatches (non-Watson-Crick pairs) in DNA.
mismatch repair (mmr)
An enzyme of E. coli that methylates adenine residues in the palindromic sequence GATC on both strands of the DNA. Transient hemimethylation of a DNA duplex following replication distinguishes the parental strand from the daughter strand.
dam methylase
scans the DNA: using
ATP it moves bidirectional on the two directions of
the strand, forming a DNA loop. The complex
scans the DNA until it finds a hemimethylated
GATC sequence
MutS-MutL complex
which unwinds DNA towards the mismatch
Helicase II
The repair of a cyclobutane pyrimidine dimer by electron transfer from a DNA photolyase
photoreactivation
A flavoprotein enzyme that becomes an electron donor when activated by visible light. DNA photolyases can repair pyrimidine dimers and other lesions caused by ultraviolet light
dna photolyase
A DNA repair pathway that involves excision of a damaged base by DNA glycosylase, followed by cleavage of the DNA backbone adjacent to the site by an AP endonuclease. Nick translation, DNA polymerization, and ligation complete the repair.
Base Excision Repair (BER)
An enzyme that hydrolyzes the N-β-glycosyl bond between a nucleotide base and pentose, creating an abasic site in the DNA.
dna glycosylase
Enzymes that cleave the DNA backbone at an AP (apurinic or apyrimidinic; abasic) site as part of the base excision repair pathway
ap endonucleases
a DNA polymerase synthesizes a new DNA strand by elongating the 3’-OH and by doing so displaces the old 5’-end of the nicked strand.
long patch repair
Pol β inserts a single
nucleotide and then a ligase completes the work.
short patch repair
A DNA repair pathway that involves excinuclease-catalyzed cleavage of the phosphodiester bond on either side of a bulky DNA lesion such as a pyrimidine dimer or base adduct, followed by removal of the segment containing the lesion, then DNA polymerization and ligation to fill the gap
nucleotide excision repair
An enzyme that cleaves a phosphodiester bond in the DNA on either side of a bulky lesion in DNA. Also called an excision endonuclease.
excinuclease
scans the DNA looking for damage during nucleotide excision repair
UvrA2 -UvrB
A nucleotide excision repair pathway in eukaryotes that is triggered when RNA polymerase encounters a lesion in the DNA and stalls.
transcription-coupled repair (TCR)
A pathway for replicating DNA across lesions that occur in unwound DNA at the replication fork. The pathway uses a TLS polymerase that lacks a proofreading exonuclease and has a less-selective active site. Although this polymerase may introduce a mutation, it allows replication to proceed.
translesion synthesis (TLS)
