DNA Repair Flashcards
3 types of DNA repair
Base excision repair
Nucleotide excision repair
Mismatch repair
Base Excision Repair and how it works
Base got modified
1. DNA glycosylase removes base
2. AP endonuclease breaks backbone 5’ end
3. Exonuclease breaks backbone as 3’ end
Now have a OH group at 5’ spot
4. DNA polymerase comes in puts DNA down, runs into DNA
5. Ligase seals it up
When does DNA repair happen
-In the g1 and g2 phase
-need it fixed before s-phase happens
-if a mutation is sitting in g1 and g2 it is not an issue yet
Nucleotide Excision Repair
Fixes Thymine Dimers
-Protein UVR Ax2 and B slide down the DNA looking for dimers.
-When it reaches a dimers B remains and A’s let go.
-B is on the dimers the UVR C will bind cuts a few bases upstream and downstream from dimer.
-UVR D dislodges the strand that was cut.
-DNA polymerase and ligase come in to finish.
Xeroderma Pigmentosum
UVR A is mutated so it can’t bind to B so it will not be able to cut out dimers and cause this disease
Mismatch Repair
When bases are mismatched with each other
-On our DNA there should be a GATC sequence and a match of CTAG
-On the older strand there will be a methyl group
-The methyl group is considered the correct base/sequence
-Mut s binds to the wrong base
-Mut H binds to the palindromic sequence how every far away
-Binds more on the non-methyl group but is touching both
-Mut L links S and H together
-Mut L binding to mut H causes a nick in the non methylated strand
-Exonuclease then chews all the way to the Mut S
-DNA polymerase and Ligase come though putting the right base down
How come some animals that have lots of offspring have such a low repair system
Due to how many offspring that they are producing in how much time they do not need to take the time to fix there DNA because of the rates that there lineage gets carried on but for animals where you only get one offspring in 9 months or in a year the DNA better be perfect because it take a long time for a next generation to occur
Who discovered transposons
Barbara McClintock
What do transposons have
Inverted repeats on their ends
Class II transposons
-IR regions in the genome
-Enzymes that recognize the IR repeats cut it out then move it
-Cuts out the IR to the other IR spot moves that whole thing to another spot
-Could get inserted into a whole other chromosome
What can transposons cause
Depending on where the transposons get placed it can mess up how the gene get copied and make an incorrect protein
-it could mess up the promoter eliminating the gene all together
-But it could also cause no problems if its outside the gene
Class I transposons
-Have an RNA intermediate
-Double stranded DNA get coded
-RNA polymerase
-RNA form
-Reverse transcriptase
-Then back to a double stranded DNA
-This double stranded DNA can be impeded into a different chromosome or the same chromosome
Will you always have the same number of transposons
In class 2 what you start with is what you will always have but in class 1 you accumulate transposons so there will be some addition
What are type 2 transposons also considered
Jumping genes
What do type 1 transposons do to the gene
Amplifying gene regions
