Question

Define 3 mutations and mention if a functional protein is made after translation or transcription of each type.

Answer 1

Permanant change occurs in the nucleotide sequences of DNA during replication of recombination can be termed as "mutation".There are 3 types of DNA mutations.

■ Base Substitution mutation

Single base substitutions called point mutations.Most common type of mutations which are of two types mainly.

▪Transition: Occurs when a purine is substituted with another purine or when a pyrimidine is substituted with another pyrimidine.

▪Transversion: occurs when a purine is substituted with a pyrimidine or a pyrimidine replaces a purine.

At the level of translation, point mutations often manifest as functional changes in the final protein product. Thus, there exist functional groupings for point mutations.

Point mutations that occur in DNA sequences encoding proteins are either silent, mis-sense or non-sense.

•silent mutation:Silent mutations result in a new codon (a triplet nucleotide sequence in RNA) that codes for the same amino acid as the wild type codon in that position.
•Mis-sense mutations:Substitutions that result in functionally different amino acids.These can lead to alteration or loss of protein function.
•Non-sense mutations: Result in a stop codon in a position where there was not one before, which causes the premature termination of protein synthesis and a complete loss of function in the finished protein.


■.Deletion mutation

Resulting in a frameshift when one or more base pairs are lost from the DNA .

If one or two bases are deleted the translational frame is altered resulting in a garbled message and non functional product.

■ Insertion mutation

The insertion of additional base pairs may lead to frameshifts depending on whether or not multiples of three base pairs are inserted. A frameshift mutation shifts the grouping of these bases and changes the code for amino acids. The resulting protein protein is usually non functional.