Depurination can produce transversion mutations
(1) In the
original
intact dsDNA molecule,
G pairs with C. (2) In one ssDNA strand, hydration
of the bond between the base and the sugar leads to the loss of
the G
base (depurination), while
leaving
the sugar-phosphate backbone intact. (3) When this strand is
replicated, DNAPol
copies the 'blank' apurinic position by
incorporating a random base (in this example, A) in
the
newly synthesized
strand. (4) Replication of that strand replaces the
original G
/
C pair with a
T / A pair. The result
is a G
T
transversion
mutation.
[HOMEWORK: Can random base incorporation at an apurinic site give rise to a transition mutation? Explain why or why not, using the above example].
Depurination in
intact dsDNA is
ordinarily
repaired in vivo by
proof-reading polymerases. DNA
in
non-living forensic or palaeontological material is not subject
to
repair, and the accumulation over time of apurinic sites
prevents such 'ancient DNA' (aDNA)
material from being correctly
read by the polymerase
chain reaction.