MUTATION -PART II NONSENSE MUTATION:Premature chain termination of the protein is caused by the non-sense mutation.The nonsense mutant codons are- UAG (amber); UAA (ochure) and UGA (opal).
Nosuch corresponding species of tRNA is observed in this case. The binding of anytRNA is not stimulated by the UAG; UAA and UGA.The prematured terminated protein or peptide fragment wouldcompletely lose its activity in the nonsense mutation. After that, it leads tothe lethal mutation. The mutation due to which the survival of organisms isprevented is known as the lethal mutation.
Properties of Point mutants1. Point mutants are leaky mutants. Leaky mutantsare the type of mutants which possess some residual level of gene expression orfunction.2. Nonsense, missense and silent mutation are givenrise by these mutants.3.
They possess a much higher reversion rate thanthe insertion or deletion mutants. Difference between the point mutation and frame shiftmutation POINT MUTATION FRAME SHIFT MUTATION 1. Occur due to the substitution of base pair. 1.
The insertion or deletion of single base or more than one base gives rise to the frame shift mutation. 2. Reversion rate is high. 2. Rate of reversion is low.
3. Chemical mutagens are able to increase the frequency of the point mutation. 3.
Chemical mutagens do not effect the frame shift mutation. 4. Examples are base analogs like 5-bromo uracil and chemical mutagens like HNO2.
These cause the point mutation. 4. Frame shift mutation is caused by the intercalating agents like acridine orange. Spontaneous mutation: Spontaneous mutation can beobserved in all organisms. It is a certain type of mutation which is obtainedas a result of some normal cellular operations like replication orrecombination or by some random interactions with the environment. It can be caused by UV irradiation. Covalent bonds betweentwo adjacent base can be introduced by this UV irradiation and results in theformation of intrastrand thymine dimer in DNA. Induced mutation: Treatment with some chemical agentsor compounds can increase the rate of the induced mutation.
These chemicalcompounds are known as mutagens and the changes which are caused by them isknown as the induced mutations. Mutagens: They can be classified in different groups.These are as follows,A.
Deaminating agents like HNO2.B. Alkylating agents like dimethyl sulphate;nitrogen mustard and ethylnitrosourea.
C. Acridine dyes like actinomycin.D. Base analogs like 2-amino purine; 5-bromouracil.