Problem :
How does the 3' to 5' proof-reading exonuclease work?
The proof-reading exonuclease scans the newly synthesized DNA strand in the
opposite direction
of DNA replication for errors in base pairing. When it finds an error, it cuts
the incorrect base
pair from the newly synthesized strand out and the entire replication holoenzyme
backs up and
attempts to introduce the correct base all over again.
Problem :
Where does the exonuclease cut the daughter strand to remove an improperly
paired
base?
The exonuclease cleaves the phosphodiester bond that is located between the
phosphate group of
the incorrect base and the 3' –OH of the previous base on the daughter strand.
Problem :
What are the three main sources of DNA damage?
The three main sources are hydrolysis, chemical damage, and radiation damage.
Problem :
Thymine dimer mutations are corrected by what DNA repair system?
Short-patch excision repair system.
Problem :
In the mismatch repair system, how does the exonuclease distinguish which base
is the correct one?
Adenine bases that are located on the original or parent DNA strand are
methylated during
replication. When the mismatch repair exonuclease finds a mismatched base pair,
it removes the
base that is on the strand that lacks methylated adenines.
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