BCHM 3050 1st Edition Lecture 5 Outline of Last Lecture I Weak Acids II Ionization of Water III Buffers IV Henderson Hasselbalch Equation V Types of Buffers VI Amino Acids Outline of Current Lecture I Isoelectric Point pI a Nature of an Amino Acid b Nonpolar Amino Acids c Acidic Amino Acids d Basic Amino Acids Current Lecture I Isoelectric Point pI a Nature of an Amino Acid i When determining the nature of an amino acid just look at the R group the rest of the amino acid is considered the backbone ii The R group determines if the amino acid is polar nonpolar acidic or basic b Nonpolar Amino Acids i At extremely low pH amino acid will hold onto the proton ii At pH of zero most amino acids that are nonpolar will has a net charge of 1 iii At pK 2 3 proton will leave COOH group to create COO1 pH at which 50 carboxylic acid groups have charge of zero and 50 have charge of 1 iv At pK 6 0 all COOH lost protons to become COO These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute v At pK 9 7 50 NH3 and 50 NH2 vi pI the average of 2 3 and 9 7 which is 6 0 c Acidic Amino Acids i For Aspartic Acid at pH of 2 1 50 has a charge of 1 and 50 has a charge of 0 ii At 3 9 50 has charge of 0 and 50 has charge of 1 iii Amino group loses protons last iv pI of acidic amino acid average the pK of the 2 carboxylic acid group DO NOT take into account the pK of the amino group v Average pK 1 and pK 2 for ACIDIC AMINO ACIDS ignore pK 3 d Basic Amino Acids i For Basic amino acids pI pK 2 pK 3 2 ii Average the two higher numbers iii Ignore the pK 1 value
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