Mutation in the Codon which causes a Change in the Coded Amino Acid | Medical PG Preparations

A mutation in the codon which causes a change in the coded amino acid is commonly termed as 

A. Mitogenesis 
B. Somatic mutation
C. Missense mutation 
D. Recombination

Ans. C.  Missense mutation.  

Point mutation

In this mutation, there is a substitution of single base in a nucleotide. 

Effect of point mutation:

Missense effect—When a different amino acid is incorporated into protein. 

Acceptable mutation: In this case, a change in amino acid will produce the protein that functions according to body requirement. Therefore, there is no clinical manifestation. For example, in the normal case at beta 67th position valine is present which is replaced by 

-  Alanine in Hb Sydney,

-  Aspartate in Hb Bristol, 

-  Glutamate in Hb Milwaukee. 

• Partially acceptable: Sickle cell anemia, hydrophilic glutamate is substituted to valine at beta 6th position. 

• Unacceptable mutation: In this case, a change in a single amino acid makes the protein nonfunctional and may incompatible with life. For example, change of histidine to tyrosine at w-chain in heme metabolism leads to the formation of met hemoglobin HbM. . This results in considerable decrease in O2 carrying capacity of hemoglobin.