PROTEINS Polymer of amino acids linked by amide linkage. Functions: 1. Nutritional: growth, digestion, metabolism (enzymes). 2. Physical structure: cheese, bread, foaming agent, gelforming
PROTEINS Polymer of amino acids linked by amide linkage. Functions: 1. Nutritional: growth, digestion, metabolism (enzymes). 2. Physical structure: cheese, bread, foaming agent, gelforming
Amino Acids C H HO C H CH 2OH O O C OH NH2 C H CH 3 L -Glyceraldehyde L - Alanine Zwitterion O C OH NH 2 C H CH 3 O C O - NH 3 + C H CH 3
Amino Acids C H HO C H CH 2OH O O C OH NH2 C H CH 3 L -Glyceraldehyde L - Alanine Zwitterion O C OH NH 2 C H CH 3 O C O - NH 3 + C H CH 3
Evidence of Zwitterion in Amino Acids at Neutral pH N H3 + CH2 C OO CH3COOH CH3CH2N H2 CH3 C OCH3 CH2 NH3 + O 1. At Neutral pH CH3CH2COOH CH3 CH CH3 NH2 CH3 CH C O - NH3 + O Melting Point -101 C 295 C 22 C 2
Evidence of Zwitterion in Amino Acids at Neutral pH N H3 + CH2 C OO CH3COOH CH3CH2N H2 CH3 C OCH3 CH2 NH3 + O 1. At Neutral pH CH3CH2COOH CH3 CH CH3 NH2 CH3 CH C O - NH3 + O Melting Point -101 C 295 C 22 C 2
L is naturally-occurring form for amino acids. Ionizable groups Zwitterion pKa for pKb for What form do we get at pH = 1? pH = 3.5? pH = 7.5? pH =9.5? and pH = 11.5? C OH O NH2 C OH O = 2.2 NH 2 = 9.5
L is naturally-occurring form for amino acids. Ionizable groups Zwitterion pKa for pKb for What form do we get at pH = 1? pH = 3.5? pH = 7.5? pH =9.5? and pH = 11.5? C OH O NH2 C OH O = 2.2 NH 2 = 9.5
DISSOCIATION OF THE CARBOXYL GROUP (pKa) R C COONH3 + H H NH3 + R C COOH + H+ H + K1 = H NH3 + R C COOR C COOH NH3 + H H + = K1 H NH3 + R C COOH R C COONH3 + H pH = pK1 Log H NH3 + R C COOR C COOH NH3 + H [ ] +
DISSOCIATION OF THE CARBOXYL GROUP (pKa) R C COONH3 + H H NH3 + R C COOH + H+ H + K1 = H NH3 + R C COOR C COOH NH3 + H H + = K1 H NH3 + R C COOH R C COONH3 + H pH = pK1 Log H NH3 + R C COOR C COOH NH3 + H [ ] +