mutations and repair Flashcards
what does it mean by genetic code is universal?
all living things use the same 4 bases and codons code for the same amino acid regardless of which organism it is in
what does it mean by genetic code is redundant?
more than one codon can code for the same amino acid AGA and AGG both code for Arg
AND
some tRNAs recognize more than one codon
what does it mean by genetic code is non ambiguous?
each codon only specifies one amino acid so a codon can’t code for more than one amino acid
what is the wobble hypothesis
base pairing rules are flexible in the wobble position which is the third base of the mRNA codon and its corresponding tRNA anticodon
what is inosine? what can it do?
a modified form of adenine found in tRNA that can form hydrogen bonds with U, C, or A on the mRNA
how does inosine work in the wobble position?
the anticodon CGI can bond with GCA, GCU, or GCC which all result in the addition of the amino acid alanine (Ala)
what is a mutation?
a change in the genetic material of an organism
what is a genetic disorder or hereditary disease
a harmful mutation in gametes that are passed onto the next generation
Describe a spontaneous cause of mutation
errors in the genetic machinery during DNA replication due to enzymes
describe an induced cause of mutation
a mutation arising from exposure to mutagenic agents
what are transposable elements?
erros during recombination (crossing over)
transposons????
mutagen
a substance that can cause a mutation
what is the cause of pyrimidine dimers?
UV light
what is a pyrimidine dimer?
a type of fused base - DNA damage
what is the effect of a pyrimidine dimers
XP
describe XP
Xeroderma Pigmentosum (dry skin, change in pigmentation)
- an autosomal recessive genetic disorder that leads to the inability to repair damage caused by UV light which leads to early skin cancer
- mutation in a enzyme in the nucleotide excision repair mechanism
- individuals may need to avoid sunlight
what does intercalating mean?
distorting DNA helix between adjacent base pairs which can cause DNAP to ‘stutter’ and copy the mutagen as an extra base pair which many interfere with replication
how can a intercalating agent be used in biotechnology?
commonly used for staining and visualizing DNA in biotechnology because it inserts itself into the DNA helix and glows in UV light
what is a point mutation?
one nucleotide or base pair is altered
what are the types of point mutations:
- substitution: transition, transversion
- frameshift: insertion, deletion
what is a substitution mutation?
a small change in a DNA base pair where on nucleotide is replaced with another
what is a transition substituion mutation?
a purine to purine
OR
a pyrimidine to pyrimidine
what is a transversion substitution mutation
purine to pyrimidine
OR
pyrimidine to purine
what is a reading fram
triplet grouping codons of a genetic message
what is a frameshift mutation
number of nucelotides added/lost is not a multiple of 3 thus altering the reading frame
what is missense mutation
a mutation that does for a different amino acid it may or may not change protein function
what is a nonsense mutation? how does it effect protein function?
it codes for a stop codon which results in a truncated polypeptide, it is usually digested by the cell but in the embryoinc stage can be lethal
what is a silent mutation
a mutation that still codes for the same amino acid resulting in no change of protein function
describe exonuclease repair
mechanisms in place to proofread errors as DNA is being replicated
binds to the ends of nucleotide chain (5’ or 3’)
describe endonuclease repair
cell also continuously monitors and repairs DNA outside of replication
binds to the middle of a nucleotide chain
nuclease
an enzyme that can break phosphodiester bonds in DNA thus excising our the nucleotide
describe exonuclease proofreading and the enzymes involved
DNAP recognizes mismatches during replication
- hydrolizes the phosphodiester bonds releasing te last nucleotide that was just added
- replaces with the correct nucleotide
what mechanism of repair does endonuclease proofreading use?
nucleotide excision repair
what enzymes are involved in NER and describe what they do
- endonuclease: recognizes and binds to the error then breaks the phosphodiester bonds on the error, and the error is removed
- polymerase: replaes the gap with the correct nucleotides
- ligase: seals the ‘nick’
