Download Mutations -Gene - Mr. Lesiuk

Recall that with a GENE mutation, only one gene on the chromosome
is affected. However, many genes are crucial for producing key
enzymes and for controlling key cellular processes.
We always use mRNA
CODONS to look up
what AMINO ACIDS
that codon represents.
You never look up DNA
codons in a Genetic
Code table! If you see
the letter “T” for
thymine, you know that
a DNA codon is being
represented. Having
said all that, you will
see a couple of Google
images I use in this PPT
will state the codon in
the DNA form, just
ignore.
Healthy Gene
Mutant Gene
In a FRAMESHIFT mutation, a base is taken
In a POINT mutation, one incorrect base out OR an extra base is added in. Each
CODON from that point is shifted out of
replaces an existing base in the gene.
whack.
This only affects that one CODON.
There are three different types of POINT mutations:
1. SILENT
2. MISSENSE
3. NONSENSE
In a SILENT point mutation, one
base is substituted for another. But
there is no effect on the
sequencing of amino acids.
Because of the “DEGENERACY” of
the genetic code. Often, 3-4
different codons may still code for
the same amino acid. For example
the Codon “GAA” codes for the
amino acid “Glutamic Acid”, but
the codon “GAG” also codes for
the amino acid “Glutamic Acid”.
So there is absolutely no affect on
the resulting protein being
synthesized.
In a MISSENSE point mutation,
one base is substituted for
another. But this time, the
codon has changed in a way
that no longer makes it code
for the original Amino Acid.
For example the codon “GAA”
codes for “Glutamic Acid”. But
when the last base is changed
to a “C”, the new codon
“GAC” now codes for the
Amino Acid “Aspartic Acid”.
Although this only affect one
AA in the protein, sometimes
the protein will not take its
proper shape and will not
properly function.
In a NONSENSE point mutation,
again one base is substituted for
another. But the change to the
codon, changes it from a normal
coding codon to a “STOP” codon.
Rather than another tRNA coming in
and dropping off another amino
acid, a “Release Factor” comes into
the Ribosome and causes
“Termination” to translation. So the
polypeptide is cut off a that point. It
is impossible for the polypeptide
that formed to take on the proper
shape and function of the intended
protein. So this will always be big
trouble for the body.
There are two different types of Frameshift Mutations:
A) Deletion
B) Addition
In a DELETION frameshift
mutation, a single base is
deleted, but every single
codon from that point on
is affected. So the
resulting polypeptide is
completely messed up.
Perhaps as much as 90%
of the amino acids end
up being in the wrong
spot, not to mention that
a “Stop Codon” could
easily show up.
Different cause,
but same
results. All the
following
codons are
thrown off.
PRACTICE QUIZ:
1. Specifically name the type of Gene Mutation Shown Below:
Healthy Gene
GENE MUTATION
ANSWER : MISSENSE POINT MUTATION
Healthy Gene
Gene Mutation
ANSWER : DELETION FRAMESHIFT MUTATION
Healthy Gene
Mutant Gene
ANSWER: SILENT POINT MUTATION
Healthy Gene
Mutant Gene
ANSWER : NONSENSE POINT MUTATION