What are the similarities and differences between base excision repair and nucleotide excision repair?
Excision repair: Damage to one or a few bases of DNA is often fixed by removal (excision) and replacement of the damaged region. In base excision repair, just the damaged base is removed. In nucleotide excision repair, as in the mismatch repair we saw above, a patch of nucleotides is removed.
What is nucleotide excision repair also known as?
In nucleotide excision repair (NER), damaged bases are cut out within a string of nucleotides, and replaced with DNA as directed by the undamaged template strand. This repair system is used to remove pyrimidine dimers formed by UV radiation as well as nucleotides modified by bulky chemical adducts.
What does nucleotide excision repair do?
The primary function of nucleotide excision repair is removal of bulky adducts generated by chemicals or UV radiation, while base excision repair is the major pathway for correction of non-helix-distorting lesions such as those introduced by ionizing radiation or cellular metabolic events.
What is the function of DNA glycosylase enzyme involved in base excision repair?
Base excision repair is the mechanism by which damaged bases in DNA are removed and replaced. DNA glycosylases catalyze the first step of this process. They remove the damaged nitrogenous base while leaving the sugar-phosphate backbone intact, creating an apurinic/apyrimidinic site, commonly referred to as an AP site.
What role does AP endonuclease have in the base excision repair system?
Apurinic/apyrimidinic (AP) endonuclease is an enzyme that is involved in the DNA base excision repair pathway (BER). Its main role in the repair of damaged or mismatched nucleotides in DNA is to create a nick in the phosphodiester backbone of the AP site created when DNA glycosylase removes the damaged base.
What is at the 5 end of DNA What about the 3 end?
The 5′ end of the DNA is the one with the terminal phosphate group on the 5′ carbon of the deoxyribose; the 3′ end is the one with a terminal hydroxyl (OH) group on the deoxyribose of the 3′ carbon of the deoxyribose. One strand is said to run 5′ to 3′; the opposite DNA strand runs antiparallel, or 3′ to 5′.
What are the three steps of DNA replication?
Replication occurs in three major steps: the opening of the double helix and separation of the DNA strands, the priming of the template strand, and the assembly of the new DNA segment.
Does helicase or topoisomerase come first?
he says that the topoisomerase unwinds first then helicase comes in.