Question

What are the three steps of base excision repair?

A) Recognition, Excision, Resynthesis
B) Excision, Ligation, Polymerization
C) Incision, Ligation, Synthesis
D) Recognition, Ligation, Synthesis

Answer 1

The three steps of base excision repair (BER) are Recognition, Excision, and Resynthesis. Specific glycosylases recognize the damage, AP endonucleases excise the damaged site, and the gap is filled and sealed by DNA polymerase and ligase respectively.

Step-by-step explanation:

The correct answer to the question of the three steps of base excision repair (BER) is A) Recognition, Excision, and Resynthesis. The process of BER is critical in maintaining the integrity of DNA and is highly conserved across different organisms. Here is a step-by-step explanation of base excision repair:

1. Recognition: Specific DNA glycosylases recognize and remove damaged or incorrect bases from the DNA. This is done by cleaving the glycosidic bond between the base and the sugar, creating an AP (apurinic/apyrimidinic) site.
2. Excision: Further enzymes, including AP endonuclease, cut the DNA backbone at the AP site. This prepares the DNA for the insertion of a correct base.
3. Resynthesis: DNA polymerase then adds the correct nucleotides to fill in the gap that was created by the removal of the damaged base. Finally, DNA ligase seals the repaired DNA strand by forming a phosphodiester bond, restoring the integrity of the DNA molecule.

It is important to note that nucleotide excision repair is a different pathway that targets bulks lesion like pyrimidine dimers, typically caused by UV exposure, and involves a different set of steps and enzymes.