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DNA Mutation and Repair
Terms in this set (108)
What is any change made to the DNA sequence or chromosome structure?
Although mutation can lead to death/disease, it can also create what?
Are mutations permanent?
are mutations random?
How are mutations catagorized?
a) size or type
b) what causes them
c) compatibility with life
d) how environmental conditions affect it
e) if it reverses that effect of a previous mutation
What is it called when large segments of chromosomes are deleted, inverted, moved, or duplicated?
What is it called when there are smaller changes in the DNA sequence? Even one or a few nucleotides?
if mutations were due to natural biochemical events, what kind of mutation is this?
if mutations were helped along by some artificial factor (chemical, radiation, viral), what kind of a mutation is this?
What type of mutations arise in the DNA of somatic cells? (which are normal diploid)
True or false: Somatic mutations are passed onto the next generations.
false, they are never
if mutations develop earlier in development, is it worse or better?
what type of mutation is it if they arise in the DNA of gamete-forming tissue?
are germ-line mutations passed on?
yes, they are transmitted to the offspring and onto future generations
what type of mutation is incompatible with life?
what type of mutation is it when it leads to prenatal death?
embryonic lethal mutation
if the mutation only produces an effect under certain environmental conditions, such as hot temperature, what is it called? the environment doesn't cause it--it just allows the mutations to be expressed
what is it called when the mutation reverses (suppresses) the effect of a previous mutation
What are the two types of suppressor mutations?
what occurs during an intragenic mutation?
mutation 1 alters protein structure, but mutation 2 alters it back
what occurs during an intergenic mutation?
This is when there is a second mutation in a totally different gene. mutant protein 1 is defective, so mutant protein 2 does the job of protein 1
what are the three kinds of small gene mutations (think protein)?
silent mutation, missense mutation, and nonsense mutation
what type of mutation has no effect, and is usually seen if the 3rd nucleotide of a codon changed
what type of mutation causes the wrong amino acid to be inserted?
What are three disease examples of missense mutations?
sickle-cell, cystic fibrosis, tay-sach's
what type of mutation is it if the change turns the codon into a stop codon and causes the polypeptide to stop growing?
what is it called when cells end up with an extra chromosome?
what is it called when cells end up with extra sets of chromosome?
what are the three types of aneuploidy?
monosomy, trisomy, tetrasomy
what is it called when an individual lacks 1 chromosome
what is it called when an individual has 1 extra chromosome
what is it called when an individual has 2 extra chromosomes
what are the two different types of polyploidy
what is it called when a human has a normal set of chromosomes (2n)?
what is it called when an organism has 1 extra set (3n)? 4n?
what sort of mutation is not very common in the animal world, but plants commonly undergo?
What are three autosomal trisomic conditions in humans?
1) down syndrome-- trisomy 21
2) patau syndrome-- trisomy 13
3) edward syndrome-- trisomy 18
what is the most common trisomic condition?
What causes down syndrome?
nondisjunction during meiosis 1 (usually in the mom's egg, which correlates with the mom's age)
What are the four types of rearrangement of genes?
deletions, inversions, duplications, and translocation
what are the two types of translocations?
reciprocal and non-reciprocal
Changes in chromosomal structure and arrangement are due to what?
the introduction of a chromosomal break (spontaneous or chemically induced), followed by a loss of rearrangement of the chr. pieces. When the chromosomes break, the free ends are "sticky" and will rejoin with other free ends in a nonspecific way.
What syndrome is an example of a deletion?
Cri-du-chat individuals are missing a significant portion of the small arm of what chromosome?
Cri-du-chat is an example of partial _____
when a chromsome breaks and the pieces remain apart, what determines which piece will be lost?
whatever piece has the centromere will be retained by the cell
How do duplications occur?
Improper crossing over between homologous chromosomes during prophase 1. Two nonsister chromatids should exchange the exact same genes, occasionally, however, one chromatid receives two much and the other receives too little. So, during DNA replication, the same piece is added twice.
Why are gene duplications sometimes beneficial for organisms?
Cells containing chr. duplications will be able to grow better than their normal counterpart.
Evolution requires what two things to happen?
a) formation of new alleles of existing genes
b) formation of brand new genes that encode proteins with novel functions
What is it called when a piece of a chromosome gets inverted 180 degrees within the chromosome?
How does an inversion take place?
A double chromosomal break occurs and based on where the pieces are positioned with respect to one another, they may be ligated in the wrong place.
How are inversions classified?
Based on the appearance of their arms after the event.
what are the two types of inversions?
paracentric and pericentric
what type of inversion is it if both breaks occur within 1 arm and a centromere is not involved. Arm ratios remain unchanged.
what type of inversion is it if the breaks occur in each arm. Arm ratios will be changed following ligation.
Inversions are a problem for _______ formation.
Translocation involves how many chromosomes?
Non-reciprocal translocation involves non-________ pairs
What is it called if a segment of a chromosome is transferred onto a nonhomologous chromosome?
what type of a translocation is it if 2 nonhomologous chromosomes trade random pieces?
what type of translocation is it if 1 chromosome just takes a piece from another?
How does translocation occur?
It they switch end segments, just need 2 chr. to randomly be close together and each have a break
Translocation are like inversions in that what is not lost in the process? It is just put into a different place.
When do translocations and inversions create problems?
1) The region of the chromosome near the centromere is transcriptionally inactive. If a translocation ends up moving a highly transcribed gene near the centromere, it will now be shut down.
2) Promoters tighly regulate the rate of transcription for each specific gene. if translocation ends up moving a gene to a new location so that it is under the control of a different promoter, this is very bad.
Translocations can lead to what disease?
In insertions/deletions, an extra nucleotide gets added or removed. This causes a ________, or a shift in the reading frame, and all amino acids after will be wrong.
What type of mutation causes it to go from a wild type to a mutant type?
what type of mutation causes it to go from a mutant type to a wild type?
what type of mutation causes it to go from an amino acid to a different amino acid
what type of mutation causes it to go from a sense codon to a nonsense codon?
what type of mutation causes it to go from a codon to a synonymous codon?
what type of mutation causes no change in the function?
What can happen to trinucleotide repeats?
the copy number can increase
how does DNA damage get converted into permanent mutations?
DNA now contains a wrong pair and the cell sees it as normal
What are causes of spontaneous damage?
1) errors of DNA polymerase
Polymerases and proofheading/repair enzymes are not perfect and some major causes of spontaneous errors during replication include what two things?
a) strand slippage
b) defective proofheading
jumping genes are also called
what are mobile pieces of DNA called
insertion of transposons near genes or within genes can disrupt what?
if you control transposase, you control what?
what are chemicals that resemble normal nucleotides and can substitute for them during DNA replication.
base analogs exhibit what kinda of abnoram properties?
what are flat, multiple-ringed molecules that tightly wedge themselves between the bases of DNA and distorts its 3D structure.
DNA polymerase gets confused by the intercalating agents, adds or removes a nucleotides, and causes what to happen?
insertions or deletions
what are examples of intercalating agents
ethidium bromide and acridine orange
all electromagnetic radiation have wavelenghts shorter than visible light and are very energetic. What do they disrupt?
DNA and other macromolecules
UV light causes adjacent ________ bases to fuse with one another. These are called what?
what do pyrimidine dimers prevent?
DNA polymerase from replication normally
cells containing too many of these dimers will do what to themselves?
kill themselves via apoptosis
What tests if a new chemical has to ability to mutate DNA (cause cancer)
how is the ames test set up?
-uses bacterial strain that cant make its own histidine
-mixes bacteria with either chemical or H20 and add to petri dish lacking histidine (no bacteria should grow)
-mutations can occur to allow the bacteria to make histidine, and then regain ability to grow.
what are the results of the ames test?
H2O control means very few colonies
mutagenic chemical means lots of colonies (bad)
DNA damage must be fixed before what?
how does direct repair work in thmine dimers of prokaryotic cells?
use a light dependent pathway and an enzyme called photoreactivation enzyme (PRE) to do same
PRE Is activated by blue light
what kind of DNA repair includes the removal of altered base/nucleotide and replacement with good DNA
how does excision repair occur?
1. Recognition of the lesion by 1 or more proteins and the subsequent excision
of that error by a nuclease enzyme
- Sometimes extra "good" sequence also removed
2. A DNA polymerase fills in the space with proper nucleotides
- What enzyme would you predict does this in prokaryotic cells?
3. DNA ligase seals the final nick (the last
phosphodiester bond) between the new and
• Cells have 2 types of excision repair systems
- Base excision repair
- Nucleotide excision repair
what kind of DNA repair corrects minor alterations to individual bases?
what does base excision occur?
1) DNA glycosylase enzymes recognize altered bases
- Different glycosylases recognize different types of altered
2) Glycosylase then cuts out the base only (breaking the
3) AP endonuclease enzyme recognizes the nucleotide
missing the base and makes a cut in the sugar/
phosphate backbone at that site
4) DNA pol I/ligase finish the job (and repair the damage)
Eukaryotic glycosylases have yet to be identified
What does nucleotide excision repair fix?
larger lesions that distort the actual DNA structure and block replication
how does nucleotide excision repair work?
1. DNA is damaged and a lesion forms
2. Proteins called Uvr (UvrA, B, C, D)
recognize the lesion and cut it out
- A-B complex recognizes the lesion
- A comes off and is replaced with C
- B-C together cut the DNA on either side of
- Cut out extra "good" DNA on both sides
- D is a helicase that liberates the cut piece
3. DNA pol I fills in the gap/ ligase seals
What disorder exists in which the nucleotide excision repair system is defective?
What do people with xeroderma pigmentosum experience?
- They have severe skin abnormalities when exposed to the sun
- UV light exposure Induces freckling, ulceration, and skin cancer
What does mismatch repair do?
fixes mismatches in DNA that may otherwise look okay
the problem with mismatch repair is that If the cell has a G-T mismatch, how does it know which one is correct? ( the G or the T)
Hint #1: Mismatches usually appear following DNA
- "Wrong" nucleotide is always on the new strand
- Hint #2: Newly-made DNA strands stay
unmethylated for a little while
- New and old DNA strands look different for a
short time (hemi-methylated)
- If wait too long, both become methylated
Wrong nucleotide is always on the new,
DNA commonly contains what sort of adenines?
Is there an effect on transcription because of methylated adenines?
What is the mechanism with mismatch repair?
1) MutS protein locates mismatches
- Forms complex with MutL afterward (linker)
2) MutL binds to MutH, which is bound to a nearby
- DNA must loop out to allow L-H interaction
3) MutH makes a cut in the unmethylated strand
4) MutU acts as a helicase to release the
unmethylated strand before an exonuclease
5) DNA pol III fills in with proper sequence, ligase seals
Most repair pathways require 1 good template strand
- What is done when both strands damaged?
Two repair pathways fix double-stranded breaks:
1) Homologous recombination repair (E.coli)
a) Homologous chromosome first brought in
- Usually the sister chromatid
b) RecBCD recognizes double stranded breaks
- Partially degrades 1 strand on each side
- Creates single-stranded overhangs
c) RecA binds to single-stranded end and
promotes invasion of the homologous chr.
- The good strand loops up (D-loop)
d) RuvABC, DNA polymerase, and ligase help
to recreate the gaps and resolve the structure
The once damaged chromosome will contain a piece of the homologous chr.
Very similar to what happens during crossing over
2) Non-homologous end-joining
- The two broken ends are simply glued back
- No requirement of sister chromatid
- End-binding proteins bind to each side of the
break (to stabilize)
- Cross-bridging proteins recruited to prevent
drifting of the two pieces
- Ends are processed, filled, and ligated
- Advantage Can happen any time in cell
cycle (no sister chr. required)
- Disadvantage Can lead to small deletions
near the break site (result of processing)
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