BIOS 452 Lecture Notes - Lecture 7: Titration, Histidine, Amine
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All have at least 2 titratable protons (shown below as fully protonated species) and therefore have 2 pka"s: -carboxyl (-cooh, -amino (-nh3. Some amino acids have a third titratable proton in the r group and therefore a third pka: showing all protonated: Bios 452 lecture 7 & 8 pka table for amino acids: * third column (pkar) = r group h+ Properties of amino acids in proteins and peptides are determined by the r group but also by the charges of the titratable group. Important to know which groups on peptides and proteins will be protonated at a certain ph. The degree of dissociation depends on the ph of the solution. The first dissociation is the carboxylic acid group (using glycine as an example): The second dissociation is the amino group in the case of glycine: A: look at pka table for amino acids. Cooh (pka = 2. 3) comes off first (has lower pka)
