A type of muscular dystrophy, called severe childhood autosomal recessive muscular dystrophy (SCARMD), results from a mutation in the gene for a 50-kD muscle protein. The defective protein leads to muscle necrosis. Detailed studies of this protein have revealed that an arginine residue at position 98 has been mutated to a histadine. Why might replacing an arginine with a histadine result in a defective protein?

Difference in pKa and PI values of Arginine and histadine

Explanation:

There is a huge difference between the pK values of the two amino acid groups for different groups  

For instance – for alpha CO2H group, PK value of arginine and histidine  is 2.18 and 1.78 respectively

Similarly, for NH3 group, PK value of arginine and histidine  is 9.09 and 8.97 respectively

And for R –group, PK value of arginine and histidine  is 13.2 and 5.97  respectively

Also there are difference in the isoelectronic point or isoionic point  of the two groups at a given temperature due to which the two amino acids migrate differently in an electric field.  

This give rise to a non-conservative replacement where replacement of one group by the other makes significant differences in the protein structure and function.

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explanation:

1) gene flow

- it is described as the transfer of genes from one population to another population so that frequency of gene is increased.

-a zebra migrates to join a different herd of zebras.

2) natural selection

- a mechanism of evolutionary change in which individuals with advantageous traits survive and reproduce whereas the others ( those that can not adapt) eliminate from the population.

-competition for sunlight leads to taller trees.

3) mutation

- permanent change in the nucleotide sequence of dna ( genetic material) that could have harmful or useful consequences.

-the dna of a snake changes to make its venom stronger.

4) genetic drift - it is a random phenomenon ( that occurs by chance such as fire) that results in change in the gene frequency in a small population.    

-a grassfire randomly sweeps through a population of buffalo and kills most of the animals.

explanation: