Mutation
Mutation is defined in simply words as "Stable Genetic
alteration" occurs due to change in the nucleotide sequences of a short
region of a genome, caused by either error during DNA replication or by the
damaging effects of mutagens such chemical and radiation.
Chemical Mutagens are Reactive oxygen species, nitrous acid, ethidium bromide,sodium azide etc.
Radiations are ultraviolet, gamma rays, X-rays etc.
List of Mutation types and their examples.
Mutation type
|
Definition
|
Example
|
Notes
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Transitions
|
base pair substitution (purine to
another purine and pyrimidine to another pyrimidine )
|
A --> G or G --> A (Purine), C
--> T or T --> C (Pyrimidine)
|
|
Transversion
|
base pair substitution (purine to
pyrimidine or pyrimidine to purine)
|
A --> C or C --> A, G --> T
or T --> G
|
|
Frame shift
|
Indels of number of nucleotides in a
DNA sequence (not divisible by three) can change the reading frame resulting
in a different translational.
|
Original mRNA sequence: 5′ GTC GTT
TTA CAA 3′ --> functional protein.
Frame shift mutation sequence : GTC GTT T TTA CAA or GTC GTT C
TTA CAA
|
Indels means insertion or deletion in
molecular biology.
|
Point
|
Single nucleotide is replace by a
different nucleotide
|
examples similar to transition and
transversion mutation
|
It’s a type of base substitution
mutation.
|
Silent
|
mutation is a result of substitution
occurring at the third position of the codon, but it has no effect in the
protein activity
|
GAA is mutated to GAG, but both the
codons code for small amino acid i.e. glutamate.
|
It’s a type of point mutation.
|
Missense
|
This results in change in protein
activity, since the substitution of nucleotide in the codon codes for a
different amino acid.
|
CAT which codes for histidine are
changed to CCT that code for proline.
|
It’s a type of point mutation.
|
Nonsense
|
The mutation is similar to Missense
expect that the resulting codon will be a STOP codon.
|
CAG --> TAG i.e. Glutamine to STOP
codon.
|
It’s a type of point mutation.
|
Deamination
|
Conversion of a primary amino group
to a ketone.
|
Deamination of cytosine to uracil
results in a base substitution.
|
ung gene product in E.Coli is an
enzyme that specifically removes uracil from DNA.
|
Base analogs
|
A compound similar to that of the
nitrogenous base is incorporated in the growing polynucleotide chain during
replication. It causes a stable mutation.
|
5-Bromouracil is an analog for
Thymine. So, AT --> A5BU. Now
during replication, Since 5BU is ionized, its complementary binds to G rather
than A. So A5BU results in AT and G5BU. Now during next replication, G5BU is
again gives rise to G5BU and GC.
|
It’s a stable mutation and also it
only can be induced artificially.
|
Leaky mutation
|
Amino acid substitution mutation
causes only partial disruption of the protein function.
|
A mutation makes the bacteria not to
survive in a particular medium, But the bacteria has a leaky mutation at the
mutation site, then it slowly grow on the restricted media.
|
|
Transposition mutation
|
Insertion of transposons at the site
causes this mutation.
|
It basically gives rise to antibiotic
resistance and most Multi antibiotic resistant bacteria have this mutation.
|
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