Question

How might a change in either nucleic acid (DNA or RNA) impact primary, secondary, tertiary, and quaternary protein structure? If the change, or mutation, in DNA results in several hydrophobic amino acids being replaced by several hydrophilic amino acids, how might that impact protein structure and function?

Answer 1

The deoxyribo-nucleotide sequence present in the DNA is transcribed into RNA and ribonucleotude sequence in mRNA is translated into amino acid sequence in the protein. Three ribonucleotide codes for a particular amino acid and this three nucleotide is called genetic code. Each genetic code is specific for a particular amino acid and many amino acids are coded by different genetic code which is called degeneracy of codons. So any change in codons may cause alteration in amino acid sequence although many silent mutations may occur where change in nucleotide sequence do not cause change in amino acid sequence due to degeneracy of codons. Primary structure of proteins (sequence of amino acids) affect secondary structure as well as tertiary structure. The interaction between different amino acids in protein is necessary for stable bond formation between different regions of the protein. So if the amino acid changes, this bond formation is hampered and thus proper folding is not occured. For example , f in a normal protein there is a bond between one basic and one acidic amino acid, and due to mutation, one basic amino acid is changed to either neutral or acidic amino acid, the stable bond will not form and it affect overall structure of protein. Cysteine amino acid form disulfide bond with another cysteine amino acid and if one of the cysteines is changed to any other amino acid, the disulfide bond will not form. Quaternary structure will also be affected by this type of changes.

Hydrophobic amino acids present in the interior portion of the protein where they remain associated with Vanderwal's force whereas the hydrophilic amino acids remain outside or on the surface of the proteins. So if the hydrophobic amino acids are converted to hydrophilic amino acids, the total structure will be disrupted as interior portion of the protein now orient themselves to the outside of the protein and specific interaction between amino acids will get disrupted.