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Module 8: Genetic mutations
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Lecture notes with pictures for module 8 on genetic mutations.
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Lecture 1 Dna mutations errors in replicationDNAMutations
A mutation is an alteration in the nucleotide sequence of a Dna molecule
there are two ways in which mutations can occur
a some mutations result from errors in Dna replication
these are called spontaneous mutations
are not common most Dna polymerases haveproofreading activities so are very accurate
2 some mutations are caused by mutagens
mutagens are chemical or environmental agents that cause changes in a Dna molecule
An Error in replication
the
an error in replication happens whenthere is a parent molecule
that when replicated there will be an error in the daughter
molecule change from t to c
then when it is further replicated there will be a change
from an A to a co which will cause the mutation to
be perpetuated from one single replication error
while on the other side replication will go on normally
without the mutation
some replication errors are caused by the Dna polymerase making a mistake
most mistakes occur because of base tautomerism which tricks the polymerase into putting
the wrong complementary base to the base that has been tautomerised
tautomers an isomer or isomers or a base with a slightly different chemical structure
this change changes the base pairingpotential or ability
of this adenine
so insted of base pairing with a t the imino adenine
now will base pair with a c
Normal
is
Keto thymine pairswith a enol thymine pairs with G
keto guanine pairswith c enol guanine pairs with t
only one that still pairs with original pair
, Mutagens
there are two importantways in which mutagens can cause mutations
Base analogs certain mutagens are base analogs meaning they are like a base that is able to
incorporate itself into the Dna sequence
will cause different base pairing
An important base analog is s bromo
uracil sbu
Sbu is an analog or thymine
It can getincorporated into Dna wherethymine would be
It has a bromine instead of the chs
there are different types of these bases as they can have these tonomers
n keto Sbu pairs with adenine
might be incorporated into Dna instead of t during replication
it is fine as it replaces thymine but still pairs with adenine it does notmess up the
base pairing of the Dna sequence
2 enol sbu pairs with a
very common tautomer which causes a problem
could get a Gincorporated where it does not belong and cause a mutation
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