Consider the structure of Tyrosine. Some amino acid structure diagrams group it
ID: 82463 • Letter: C
Question
Consider the structure of Tyrosine. Some amino acid structure diagrams group it with the non-polar amino acids and some group it with the polar uncharged amino acids. Why is its classification a bit ambiguous? Given what you know about tyrosine, why can you be convinced that it is polar enough to exist on the outside of folded proteins? alpha-1-Antitrypsin Deficiency disease is caused by a single codon change, resulting in a glutamic acid being changed to a lysine. Consider the chemistry of these two different amino acid residues. Why would such a change be particularly detrimental to the proper folding of the polypeptide given the knowledge that an arginine was forming an ionic bond with the glutamic acid in the tertiary structure of the unmutated version of this protein?Explanation / Answer
Ans 6 :Amino acids differ from one another based on their side chain group. Eight of the twenty amino acids fall into the hydrophobic category because their side chains contain non-polar groups. Alanine, valine, leucine and isoleucine all contain straight-chain hydrocarbon side groups. Methionine contains a straight chain hydrocarbon group that has a sulfur atom. Sulfur has the same electronegativity as carbon, which makes the methionine also non-polar. Phenylalanine, tyrosine and tryptophan all contain non-polar aromatic rings. Tyrosine and tryptophan are slightly less hydrophobic and slightly more reactive than phenylalanine because they contain an -OH and -NH group, respectively
7 amino acids are polar uncharged: gly, ser, cys, asn, gln, tyr, thr
Tyr has a special OH - due to strong electron withdrawing power of ring structure the OH is ionisable so has a pK value. Value is 10.07 so at pH 7.4 not ionised very much. However tyr used at active site of some enzymes where localised disturbance of pH can be generated and allow the ionisable OH to participate in catalysis