4.
Types
of mutation
- diagrams explaining deletion, insertion and substitution mutations
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consequences of mutations
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(4) Types
of mutation
- deletion, insertion and substitution
A mutation
causes a change in base sequence of the triplet codes for amino acids.
Deletion mutation:
A base might be deleted at random from
the DNA base sequence. Usually just one base is deleted.
This will change the way in the nucleotide
base sequence is read and will affect other bases further down the
DNA strand.
The wrong triplets are recognised so the wrong
amino acids will be coded for! So, in the diagram this section of
base sequence changes from ...
... ATC
GTT
AGC CGA ... etc. to ... ATC TTA GCC GA. ...
etc.
In other words an abnormal amino acid
sequence is produced.
This will change how the base sequence of
triplet codes is read in making RNA to code for a protein
synthesis. The mutation will have knock on effects down the
strand of DNA i.e. it may not now code for the correct sequence
of amino acids to make the appropriate protein with its correct
structure.
This might affect the protein's
structure and inhibit is function.
The correct protein might not actually
be made, with serious consequences.
Insertion mutation:
A new base may be inserted into the DNA
base sequence into a position it should NOT occupy in a gene.
This will change the way the triplet codes are
read i.e. it changes the amino acid code and code for the wrong
amino acids.
In the diagram the original triplet codons are
... ATC GTT AGC CGA ... etc. but after the insertion of base T after the
first triplet, the triplet codons now read quite differently ...
so this part of the base sequence becomes
... ATC
TGT TAG CCG A.. ... etc.
Also, as a consequence, more than one amino
acid triplet is changed because a whole sequence of bases can be
affected. The wrong amino acids will be coded for.
Again, this mutation will change how the base
sequence of triplet codes is read in making RNA to code for a
protein synthesis. The mutation will have knock on effects down the
strand of DNA and may not code for the correct sequence of amino
acids to make the appropriate protein. This might affect the
protein's structure and inhibit is function. The correct protein
might not actually be made, with serious consequences.
One or bases may be inserted in a single
mutation. If one or two bases are inserted the above applies.
BUT, if three bases are inserted, the original
sequence before and beyond the insertion remains intact! Is the
consequence an extra amino acid in the polypeptide-protein? Can the
same functioning protein still be made?
Substitution mutation:
Another base in the DNA is substituted at
random with a different base changing the base sequence.
Here there are two possible outcomes:
(i) there might not be any overall effect
because some amino acids are coded for by more than one triplet
and the substitution might make one of those other triplet
codes.
e.g. in the diagram the 2nd triplet
GTT mutated to
ATT, but may still code
for the same amino acid.
(ii) the sequence can't be read correctly
because the code doesn't match the particular amino acid
required.
The wrong amino acid will be coded for,
or, it might not code for any amino acid at all.
Again, as with other types of mutation, how
the base sequence of DNA triplet codes are read is changed, in
making RNA to code for a protein synthesis. The mutation has knock
on effects down the strand of DNA affecting the coding for amino
acids to make the appropriate protein. This affects the protein's
structure and inhibit is function and maybe the correct protein
might not actually be made, with serious consequences.
See also
the
effects of non-coding DNA
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