Chapter4a-problems - (basic R), pK1=2.20, pK2=9.40...

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1 Chapter 4: Problems Book: 1, 4-10, 12, 13, 16, 17 • Book (Ch. 4, prob. 4) Draw the dipeptide Asp-His (DH) at pH 7.0 N-term=9.40, Asp=3.90, His=6.04, C-term=2.20 N COO- CH 2 -OOC O H H H NH 3 + N H N •A c i d : – If pH<pKa, neutral (0) – If pH=pKa, (50% ionized, -0.5) – If pH>pKa, charged (-1) • Base: – If pH<pKa, charged (+1) – If pH=pKa, (50% ionized, +0.5) – If pH>pKa, neutral (0)
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2 Chapter 4: Problems Book (Ch. 4, prob. 6) Determine the net charge of the predominant form of Asp at: (a) pH=1.0 (b) pH=3.0 (c) pH=6.0 (d) pH=11.0 NH 3 + H COOH COOH NH 3 + H COO- COOH NH 3 + H COO- COO- N H 2 H COO- COO- pK 1 =2.20 pK 2 =9.40 pK R =3.90 Recall, you only need to remember the average pK 1 (2.20) and pK 2 (9,40) values and use them for all amino acids 1 0 -1 -2
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3 Chapter 4: Problems Book (Ch. 4, prob. 7) Calculate the pI of: (a) Ala (b) His, pK R =6.04 (c) Glu, pK R =4.07 Note that my answers are a little different than those at the end of the book since we are using the average pK 1 and pK 2 values!! pI=0.5(pKi+pKj), where i&j are 1&2 (neutral R), 1&R (acidic R), or 2&R
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Unformatted text preview: (basic R), pK1=2.20, pK2=9.40 pI=0.5(2.20+9.40)=5.80 pI=0.5(9.40+6.04)=7.72 pI=(2.20+4.07)=3.14 4 Book: prob. 16; ATLDAK p I charge at pH=7 Chapter 4: Problems NH 3 + N H N H N H N H N H COO-CH 3 CH 3 COO-NH 3 + O O O O O OH N-term=9.4, C-term=2.2, Asp=3.90, Lys=10.54 pI = 0.5(3.90+9.4) = 6.65 [book 0.5(3.90+8.0)=5.95] 9.4 3.90 10.54 2.2 Remove all pKas in pairs at the extremes of the pH range 2.2 , 3.90, 9.4, 10.54 Average the two values closest to the middle of the pH range X X 5 Companion, prob. 7 What percentage of histidine imidazole is protonated at pH 7.2? Chapter 4: Problems Henderson-Hasselbalch pH = pKa + log [A-]/[HA] pH - pKa = log [A-]/[HA] [A-]/[HA] = 10 (pH-pKa) = 10 (7.2-6.04) = 14.45 %HA = 100 x [HA] ([HA] + [A-]) %HA = 100 x [HA]/[HA] ([HA]/[HA] + [A-]/[HA]) %HA = 100 x 1 = 6.47% (1 + 14.45)...
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This note was uploaded on 10/05/2010 for the course BCHS BCHS 3304 taught by Professor Legge during the Spring '09 term at University of Houston.

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Chapter4a-problems - (basic R), pK1=2.20, pK2=9.40...

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