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more than one codon for some amino acids
UAA, UAG, UGA
short range frameshift
indertion of three nucleotides
proteins are encoded by
weight of aa
number of aa*110daltons
how are tRNAs charged with amino acids?
aminoacyl tRNA synthetase
nonsense mutation aa
generates stop codon
sickle cell anemia
beta chains of hemoglobin are altered due to a single amino acid change.
alters folding of the protein, forms prions
the phenomenon whereby the phenotypic expression of a gene is determined by the sex of the parent from whom it is inherited. This situation is not like a normal mutation, because it can be reversed when passed through the opposite parent.
conservative (missense) mutation
change codon and change amino acid, but that amino acid has similar biochemical functions.
one purine replaced by another, or one pyrimidine replaced by another.
one purine changed to a pyrimidine
use radiation, chemicals, and such to induce new mutation.
What is the role of DNA pol I
DNA 5' to 3' proofreading (exonuclease activity) removes RNA primers
what is the role of 3' to 5' exonuclease activity?
proofreads the most recently added deoxynucleotide and excises it if it is incorrect
what is the shifting of protons and electrons of a given base called leading to mispairing (anomalous)
what does reactive oxygen species alter?
covalent structure of bases, leading to replication errors
Which bases are purines? pyrimidines?
- purines: G or A
- Pyrimidines: C and T
what are transposons
insertion of DNA into or between genes that alter gene structure, coding capacity, transcription and regulation
what is replication slippage
looping out the leading or lagging strand during replication or slippage of the DNA polymerase, which can cause insertion or deletion of extra bases, more frequent with repetitive gene sequences called microsatelite regions
what are three trinucleotide repeat diseases?
- -Fragile X syndrome
- -Myotonic dystrophy
- -Huntington's disease
what is fragile x syndrome
contains thousands of CGG repeats in 5' UTR (untranslated). Array too long may impede expression of FMRP protein
what is myotonic dystrophy
tens of thousands of CTG repeat in 3'. increased copies mean earlier onset and more severe
what is huntington's disease
10-120 CAG repeats in coding sequence, increased number equals earlier onset.
what is the result of incorporation of 5-BU
increases probability of tautomeric shift with mispairing and altering
what groups does alkylating agents in nucleotides?
methyl or ethyl groups to amino or keto groups in nucleotide; this leads to point mutations during replication
used as chemical mutagen to perform screens for new mutants
what does aridine dye mutate cells?
intercalate with DNA helix, distorting its structure, lead to deletion or insertions of basepairs.
UV radiation, how does it mutate cells?
-damage DNA directly or create free radicals that covalently modify and damage DNA.
-Radiation can break phosphodiester bonds and chromosomal breaks.
-UV can create pyrimidine dimers (distort DNA helix)/crosslinking leading to replication errors
how does ionization induce mutations?
free radicals which can cause damage to DNA bases and backbone
what is the aim of the Ames test?
reveal the ability of chemicals to induce different types of mutations
what are the strains used in the ames test?
histidine auxotrophs with mutation that does not allow them to synthesize histidine
what is the error rate of bacteria pol iii
how much can proofreading correct the 10^-5 error rate?
99%, so 10^-7
what is mismatch repair?
when error persists after proofreading, excise the incorrect nucleotide and adds the correct nucleotide via DNA synthesis (MutL, MutS)
how does DNA recognize the correct sequence for mismatch repair?
mismatch repair is mediated by MutL/s/h that recognizes the template strand and the correct nucleotide based on the methylation on the parental strand
what is photoreactivation repair?
exposure to blue light following exposure to UV enables action of photoreactivation enzyme (PRE) not in humans but repairs thymine dimers
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