Polar amino acids

Polar Amino Acids There are twenty amino acids that occur naturally, these amino acids can be separated into two groups; non-polar amino acids and polar amino acids. The polar group consist of 10 amino acids, two are negatively charged - aspartic acid and glutamic acid, 3 have a positive charge - arginine, lysine and histidine, and 5 are uncharged - asparagine, glutamine, serine, threonine and tyrosine.^[1] The properties of the amino acid are due to the properties of the side chain or R-group. These properties are extremely important when it comes to forming protein structure as different R-groups allow different non-covalent bonds to form between amino acids in the polypeptide chain. For example only amino acids with charged R-groups can form ionic bonds with each other or with other charged molecules ^[2].
All polar amino acids have either an OH or NH2 group (when in aqueous environment), and can therefore make hydrogen bonds with other suitable groups ^[3].

Polarity of the amino acids affects the overall structure of a protein. Polar amino acid residues have a tendency to be on the outside of a protein, due to the hydrophilic properties of the side chain ^[4].
A mutation which causes an amino acid substitution can have a great affect on protein structure and therefore protein function. For example the point mutation which substitutes valine for the polar amino acid glutamate causes haemoglobin to change its shape, due to the new hydrophilic region, leading to the condition known as sickle cell anaemia ^[5]

References

1. ↑ Alberts B., Johnson A., Lewis J., Raff M., Roberts K. and Walter P. (2008) Molecular Biology of the cell, 5th edition, New York: Garland Science. (Pg 127)
2. ↑ Gupta P.K. (2009) Cell and Molecular Biology, 2nd edition, New Delhi: Rastogi Publications, p. 43
3. ↑ Alberts B, Johnson A, Lewis J, Raff M, Roberts K and Walter P (2008) Molecular Biology of the Cell, 5th edition, New York: Garland Science, p. 125 - 129
4. ↑ Alberts B, Johnson A, Lewis J, Raff M, Roberts K and Walter P (2008) Molecular Biology of the Cell, 5th edition, New York: Garland Science, p. 125 - 129
5. ↑ Chen, Harold (2006) Atlas of genetic diagnosis and counseling, Totowa, N.J. : Humana Press