BCHE 395-4 2014 Amino Acids

Pk3 pkris for the amino acids with an ionizable r

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Molecules Proves Truly Valuable! EssenQal vs. NonessenQal •  EssenQal amino acids are those that an organism MUST obtain through the diet –  Humans: T, W, V, R, H, K, F, L, I, M, –  These Ten Valuable Amino acids Have Long Preserved Life In Man. (mnemonic) –  Threonine (T), Tryptophan (W), Valine (V), Arginine (R), HisQdine (H), Lysine (K), Phenylalanine (F), Leucine (L), Isoleucine (I), Methionine (M) –  Non- essenNal are those an organism can synthesize Biochemistry only site www.prep4usmle.com/forum/thread/6681/ IonizaQon of Amino Acids (conjugate acid- conjugate base pairs) Ionic Forms of Amino Acids α- carbon Always has two pKs, someQmes has three A ↔ B ↔C IonizaQon of Amino Acids •  Understanding how and when amino acids lose or gain hydrogen ions is important for understanding protein structure •  Each α- COOH, α- NH2 and some R groups have own pK for their protons (H+) Weak acids Conjugate pair Weak bases Conjugate pair Alanine isomerizaQon IonizaQon & Acid/Base ProperQes of Amino Acids DefiniQons! Weak base ß།OH- COO COOH O H 3 l pH OH ion H 3 H Weak acid H2 N H3 N H Conjugate pair H CO COO H3 N H H2 N CH3 Dissolve in water CH A±, or A0 Neutral pH High p COO COOH CO Zwitterion Conjugate pair H N H H3 N H H3 N 2 CH3 CH3 Low pH High pH H+à༎ COO H3 N H Alanine CH3 CH3 CH3 Neutral pHisomerizaQon pH High Low pH CH Neutral Net charges! Amphoteric: dual acid/base nature IonizaQon of Amino Acids zwieerion Net +1 charge (+) A+ Net 0 charge (0) A± Net - 1 charge (- ) A- Each ionizable group on an amino acid has a characterisQc pK value which is the –log of the dissociaQon constant X X X Obnoxious, I say! X X X More simpler- er table Amino Acids/ FuncQonal Groups •  Table of acidic and basic funcQon groups •  Can be Qtrated like a weak acid •  Amino acids have at least two pKs •  Some have 3 Rules for Assigning pKa’s to FuncQonal Groups 1.  pK1 is always the most acidic group (α- carboxyl) 2. pK2 is the α- amino group (not always the most basic group) 3. pK3 (pKR)is for the amino...
View Full Document

This note was uploaded on 03/02/2014 for the course BIOCHEMIST 395 taught by Professor Potenza during the Spring '14 term at NMSU.

Ask a homework question - tutors are online