chapter 11 part 1 Flashcards
what are germ-line mutations?
mutations that occur in germ-line cells giving rise to sperm & egg
can germ line mutations be passed on from one generation to the next?
yes
what are somatic mutations?
mutations not in the germ line cells
what are cells not in the germ line called?
somatic cells
will somatic mutations be passed on?
they will only be passed on to direct descendants of the original mutated cell
they divide my mitosis
what do gene mutations do to one or more DNA base pairs?
substitute, add, or delete one or more base pairs
what are point mutations and where do they occur
they are localized mutations that occur at a specific, identifiable position in a gene
what are genes with elevated mutation rates called?
mutation hotspots
-large gene size, regions rich in CpG dinucleotides, long stretches of trinucleotide repeats
what is the DYS gene associated with?
Duchenne muscular dystrophy
what is the NF1 gene associated with?
neurofibromatosis are large genes each with a mutation rate of about 10^-4
what is a base pair substitution mutation from purine to purine or pyrimidine to pyrimidine called?
transition
what is a base pair substitution mutation from pyrimidine to purine and vise-versa called?
transversion
what are the types of base-pair substitution mutations>
silent (synonymous) mutation
missense mutation
nonsense mutation
silent (synonymous) mutation
a type of bp mutation where there is no amino acid change
missense mutation
a type of bp mutation where there is a change in amino acid
nonsense muation
a type of bp mutation where a stop codon is created
what is a frameshift mution
insertion or deletion of one or more base pairs altering the reading frame of the message
what are frame shift mutations also called
INDEL mutions
-INsertion or DELetion mutations
what results from a frameshift mutation?
the wrong amino acid sequence is produced downstream of the altered nucleotides
-premature stop codons are commonly encountered
what are promoter mutations
mutations that alter consensus sequence nucleotides of promoters
what do promoter mutations interfere with?
interfere with efficient transcription initiation
what is a splicing mutation?
when the specific splicing sequence is altered due to a mutation
what requires specific sequences at either end of the intron?
splicing
efficient splicing of introns from mRNA requires specific sequences at either end of the intron
what do splicing mutations result in?
result in splicing errors & the production of mutant proteins due to the retention of intron sequences in the mRNA
what do some base-pair substitutions do?
they produce new splice sites that replace or compete with authentic splice sites during mRNA processing
what are cryptic splice sites?
when a base-pair substitution mutation results in a new splice site that replaces or competes with the authentic splice sites during mRNA processing
polyadenylation mutations
mutations of the polyadenylation signal sequence at the 3’ end of eukaryotic mRNA can block the proper 3’ processing of mRNA
where do we know of that polyadenylation mutations occur?
in a rare mutant form of the human beta globin gene, leading to severe reduction in functional beta globin protein produced
forward mutation
convers a wild-type allel to a mutant allele
reverse mutations are also called what
reversion mutations
reverse mutation
converts mutant alleles to wild-type or near wild-type
true reversion
wild-type DNA sequence (or amino acid sequence) is restored by a second mutation with the same codon
intragenic reversion
occurs through mutation elsewhere in the same gene
second site reversion
occurs by mutation in a different gene & together the two mutations restore the organism to wild-type
what are second site mutations also known by and why?
suppressor mutations since the second mutation “suppresses” the mutant phenotype caused by the first mutation
spontaneous mutations
arise in cells without exposure to agents capable of inducing mutation (mutagens)
how do spontaneous mutations primarily arise?
through errors in DNA replication or spontaneous changes in the chemical structure of a nucleotide base
does DNA replication have high or low fidelity?
very high do to the DNA polymerases ‘proofreading’ ability as well as their accuracy & efficiency of mismatch repair
what rate do mismatches due to replication errors occur?
about 1 x 10^-9 in wild type e.coli & about the same in eukaryotes
what does alteration in number of DNA repeats occur via?
strand slippage
strand slippage
the DNA polymerase of the replisome temporarily dissociates from the template & a portion of the newly replicated DNA forms a temporary hairpin
-resumption of replication leads to re-replication of some of the repeats & an overall increase in the number of repeats on the daughter strand
what are trinucleotide repeat disorders?
a special class of mutations causing some hereditary diseases in humans & other organisms
-wild-type alleles of the genes in question have a characteristic number of DNA trinucleotide repeats
-increases in the number of repeats beyond a certain threshold causes the disorders
what is depurination
the loss of a purine from a nucelotide by breaking the covalent bond linking the nucleotide base to the sugar
what is a lesion of depurination called?
apurinic sitte
are most apurinic sites repaired before replication?
yes
what happens if apurinic sites are left unrepaired?
DNA polymerase will usually compensate by putting adenine into the site during replication
what is deamination?
the loss of an amino group (NH2) from a nucleotide
what happens when cytosine is deanimated?
an oxygen atom usually takes its place, converting the cytosine to uracil
-DNA mismatch repair removes the uracil from the DNA & replaces it with cytosine, restoring the wild-type sequence
what happens when methylated cytosine is deaminated?
a thymine base is produced, which is now base-paired with guanine
-mismatch repair system can restore the wild-type G-C pair
-if repair does not occur, replication will produce two sister chromatids, one with mutant A-T pair & one with the wild-type G-C pair
