BIOL 2112 Lecture Notes - Lecture 5: Cell Membrane, Aspirin, Histidine
19 Nov 2018
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Document Summary
The pka of a protein is the summation of all the pkr values of ionizable side chains on the surface of the protein. Amino acids have unique titration curves because they have several ionizable groups, each with its own dissociation constant. Slide 13 shows the ionization of the amino acid glutamate and the ionization constants for the carboxyl group (pk1) and the amino group (pk2). Certain amino acids also carry ionizable groups on their side chains, denoted as pkr (as in r group). Buffering ability is approximately one ph unit on either side of the pkr. The amino acid whose pkr is closest to the ph of the cytoplasm, has the best ability to act as a buffer in that environment. In short, the closest to ph 7, the better the buffering capacity in the cytoplasm. Amino acid: histidine > tyrosine > aspartate > lysine > arginine pkr: 6. 0 10. 07 3. 65 10. 53 12. 48: aspirin has a pka of 3. 5.
