DNA repair mechanisms Flashcards
What enzymes are involved in the repair mechanism acts on depurinated bases
AP enduclease which nicks the DNA, DNA polymerase I and ligase
What molecule can extend the depurinated base pair mechanism to repair other types of damage to DNA bases?
DNA Glycosylase
What is an example of damage done to DNA by U.V. light?
Thymine Dimer formation
What is the repair mechanism of thymine dimers?
Helicase unwinds DNA segement with the dimer, Uvarb nuclease nicks the dimer, then DNA pol. 1 and ligase repair the DNA strand
What is the difference between the repair of thymine dimers in humans and in humans
Humans use more polypeptides and remove more nucleotides
What disease is caused by a compromised thymine dimer repair mechanism?
Xeroderm Pigmentosa
What is the mechanism for mismatch repair?
Mut S binds to the DNA strand with the error, and Mut H binds to the old DNA strand, Mut L then combinesthe two proteins allowing formation of a hairpin loop, the DNA is the unwound and the new strand- identified by a lack of methylation- is cut followed by DNA pol. 1 and ligase repair
What is the difference between the mismatch repair mechanism in eukaryotes?
MSH 2, MSH 6 are recognition proteins, MLH 1 is the joining protein which forms a loop
What are the two methods used to repair a double strand break?
Recombinational Repair or the mechanism used in the stress response
What is recombinational repair?
When there is a double strand break, nucleases degrade the DNA to produce sticky ends, these are protected by proteins like RAD 51 this is beneficial as then one end of the DNA will search for a homologous region on its sister chromosome, when that region is found these two regions base pair resulting in the searching strand being able to be elongated , the searching strand then goes to the other broken strand and is used as a template allowing repair of the strand break with information being more likely to be retained
What is the method of repairing double strand breaks as seen in the stress response?
Any sticky ends are degraded by nucleases, and the strands are then joined together by a ligase this results in permanent loss of genetic information
