EBK ORGANIC CHEMISTRY
8th Edition
ISBN: 8220102744127
Author: Bruice
Publisher: PEARSON
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Chapter 21, Problem 56P
A professor was preparing a manuscript for publication in which she reported that the p1 of the tripeptide Lys-Lys-Lys was 10.6. One of her students pointed out that there must be an error in her calculations because the pK2 of the ε-amino group of lysine is 10.8 and the p1 of the tripeptide has to be greater than any of its individual pKa values. Was the student correct?
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A professor was preparing a manuscript for publication in which she reported that the pI of the tripeptide Lys-Lys-Lys was 10.6. One of her students pointed out that there must be an error in her calculations because the pKa of the e-amino group of lysine is 10.8 and the pI of the tripeptide has to be greater than any of its individual pKa values. Was the student correct?
T11.1. A student was provided with the following compounds: (i) N-acetyl-L-Aspartic acid (ii)
tert-butyl amine and (iii) coupling agent N,N'-dicyclohexylcarbodiimide (DCC) – to create
peptide(s). The synthesis was successfully completed at 100% conversion, where a 2:1 ratio of the
amine to amino acid was used and all possible peptide bonds were formed. If partial racemization
also took place during the synthesis, how many types of product(s) can the student possibly obtain
from the reaction?
HO.
CH,
OH
Ö HN.
CH,
H,C
NH2
(A) 1 (B) 2 (C) 3 (D) 4 (E) 5 (F) 6 (G) None of these
T11.2. Referring to T11.1: assuming the synthesis was successfully completed at 100%
conversion ONLY to form Dipeptide(s) while partial racemization also took place, how many
types of Dipeptide product(s) can the student possibly obtain from the reaction?
(A) 1 (B) 2 (C) 3 (D) 4 (E) 5 (F) 6 (G) None of these
Peptides can be separated using an ion-exchange column based on their isoelectric (pI) values. At which pH values would
two different peptides, one with a pl of 5.6 and the other with a pl of 8.6, bind to a cation- and anion-exchange column?
Each peptide may be capable of binding to each column at more than one pH value.
anion-exchange column at
pH = 4.0
pH = 6.5
pH
=
10.1
cation-exchange column at
= 4.0
pH
pH =
pH
= 6.5
= 10.1
Answer Bank
peptide B pl = 8.6
peptide A pl = 5.6
Chapter 21 Solutions
EBK ORGANIC CHEMISTRY
Ch. 21.1 - a. Explain why, when the imidazole ring of...Ch. 21.2 - a. Which isomer(R)-alanine or (S)-alanineis...Ch. 21.2 - Prob. 4PCh. 21.3 - Prob. 5PCh. 21.3 - Prob. 6PCh. 21.3 - Draw the predominant form for glutamate in a...Ch. 21.3 - a. Why is the pKa of the glutamate side chain...Ch. 21.4 - Calculate the pI of each of the following amino...Ch. 21.4 - a. Which amino acid has the lowest pI value? b....Ch. 21.4 - Prob. 12P
Ch. 21.4 - Prob. 13PCh. 21.4 - Explain why the pI of lysine is the average of the...Ch. 21.5 - What aldehyde is formed when valine is treated...Ch. 21.5 - Prob. 16PCh. 21.5 - Prob. 17PCh. 21.5 - Prob. 18PCh. 21.5 - Prob. 19PCh. 21.6 - Why is excess ammonia used in the preceding...Ch. 21.6 - Prob. 21PCh. 21.6 - What amino acid is formed using the...Ch. 21.6 - Prob. 23PCh. 21.6 - What amino acid is formed when the aldehyde used...Ch. 21.7 - Esterase is an enzyme that catalyzes the...Ch. 21.8 - Draw the tetrapeptide Ala-Thr-Asp-Asn and indicate...Ch. 21.8 - Draw the resonance contributors of the peptide...Ch. 21.8 - Which bonds in the backbone of a peptide can...Ch. 21.9 - An opioid pentapeptide has the following...Ch. 21.9 - What is the configuration about each of the...Ch. 21.9 - Glutathione is a tripeptide whose function is to...Ch. 21.10 - What dipeptides would be formed by heating a...Ch. 21.10 - Suppose you are trying to synthesize the dipeptide...Ch. 21.10 - Show the steps in the synthesis of the...Ch. 21.10 - a. Calculate the overall yield of bradykinin when...Ch. 21.11 - Show the steps in the synthesis of the...Ch. 21.13 - Prob. 37PCh. 21.13 - In determining the primary structure of insulin,...Ch. 21.13 - A decapeptide undergoes partial hydrolysis to give...Ch. 21.13 - Explain why cyanogen bromide does not cleave on...Ch. 21.13 - Indicate the peptides produced from cleavage by...Ch. 21.14 - Prob. 43PCh. 21.14 - Three peptides were obtained from a trypsin...Ch. 21.14 - Prob. 45PCh. 21.15 - How would a protein that resides in the nonpolar...Ch. 21.16 - a. Which would have the greatest percentage of...Ch. 21.17 - When apples that have been cut are exposed to...Ch. 21 - Glycine has pK2 values of 2.34 and 9.60. At what...Ch. 21 - Prob. 50PCh. 21 - A titration curve is a plot of the pH of a...Ch. 21 - Prob. 52PCh. 21 - Aspartame (its structure is on page 1007) has a pl...Ch. 21 - Draw the form of aspartate that predominates at...Ch. 21 - Show how phenylalanine can be prepared by...Ch. 21 - A professor was preparing a manuscript for...Ch. 21 - What aldehydes are formed when the following amino...Ch. 21 - Prob. 58PCh. 21 - Determine the amino acid sequence of a polypeptide...Ch. 21 - Prob. 60PCh. 21 - Prob. 61PCh. 21 - Which is the more effective buffer at...Ch. 21 - Identify the location and type of charge on the...Ch. 21 - Draw the product obtained when a lysine side chain...Ch. 21 - After the polypeptide shown below was treated with...Ch. 21 - Treatment of a polypeptide with 2-mercaptoethanol...Ch. 21 - Show how aspartame can be synthesized using DCCD.Ch. 21 - -Amino acids can be prepared by treating an...Ch. 21 - Reaction of a polypeptide with carboxypeptidase A...Ch. 21 - a. How many different octapeptides can be made...Ch. 21 - Glycine has pKa values of 2.3 and 9.6. Do you...Ch. 21 - A mixture of 15 amino acids gave the fingerprint...Ch. 21 - Write the mechanism for the reaction of an amino...Ch. 21 - Prob. 74PCh. 21 - Show how valine can be prepared by a. a...Ch. 21 - The primary structure of -endorphin, a peptide...Ch. 21 - A chemist wanted to test his hypothesis that the...Ch. 21 - Propose a mechanism for the rearrangement of the...Ch. 21 - A normal polypeptide and a mutant of the...Ch. 21 - Determine the amino acid sequence of a polypeptide...
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Need a deep-dive on the concept behind this application? Look no further. Learn more about this topic, chemistry and related others by exploring similar questions and additional content below.Similar questions
- 22-61 Polyglutamic acid (a polypeptide chain made only of glutamic acid residues) has an a-helix conformation below pH 6.0 and a random-coil conformation above pH 6.0. What is the reason for this conformational change?arrow_forwardOn complete hydrolysis, a polypeptide gives two alanine, one leucine, one methionine, one phenylalanine, and one valine residue. Partial hydrolysis gives the following fragments: Ala-Phe, Leu-Met, Val-Ala, Phe-Leu. It is known that the first amino acid in the sequence is valine and the last one is methionine. What is the complete sequence of amino acids?arrow_forward22-71 Which amino acid side chain is most frequently involved in denaturation by reduction?arrow_forward
- 22-31 A polypeptide chain is made of alternating valine and phenylalanine. Which part of the polypeptide is polar (hydrophilic)?arrow_forwardCalculate the percentage ionization (i.e. [base]/[acid]x100) in these amino acid side chains at the pH values specified (show your work for one of these amino acid chains): - Aspartate (pKa=4.1) at pH 5.4 - Arginine (pKa=12.5) at pH 11.8 - Histidine (pKa=6.0) at pH 8.0 - Tyrosine (pKa=10.9) at pH 8.0arrow_forwardThis is a three-part question about a tripeptide. Answer all three sub-questions. The pKR of side chains of Tyr, and Lys is 10.46 and 10.54 respectively. The molecular weight of amino acids Ala, Lys, and Tyr in neutral form is 89.1, 146.2, and 181.2 Da, respectively. 1) Draw the chemical structure of the dominant form of tripeptide AKY at pH = 11.5, ensure you have the correct stereochemistry and ionization state of each functional group (Hint, lysine has a C-epsilon as the furthest carbon from C- alpha). 2) Calculate the pl of tripeptide AKY, assuming the terminal amino group has a pKa of 8.0, and the terminal carboxyl group has a pKa of 3.5 i^ 3) Calculate the molecular weight of AKY at pl (arrow_forward
- All amino acids have two ionizable functional groups: an α‑amino group (average pKa of 9.4) and an α‑carboxylic acid group (average pKa of 2.2). Aspartic acid has an ionizable side chain (R group) with a pKa of about 3.8. One of the possible ionization states of aspartic acid is shown in the image. At what pH would the structure be the predominant ionization state? Consider the ionization state of all three of the functional groups.arrow_forward8. The following proteins represent a wide range of molecular weights and isoelectric points. Mr is the molecular weight of a single protein chain. • Protein 1: Mr 68,544; pl 6.11 (monomer) • Protein 2: Mr 29,041; pl 5.32 (dimer) • Protein 3: Mr 15,805; pl 5.7 (dimer) • Protein 4: Mr 12,165; pl 4.74 a. Which protein is the most acidic? Explain your answer. b. Which protein will migrate the slowest in an SDS-PAGE? Explain your answer. c. In what order will these proteins elute from a cation exchanger at pH 8? Explain your answer. d. In what order will these proteins salt out from a pH 7 solution by the dropwise addition of saturated ammonium sulfate? Explain your answer. 5 83°F Cloudyarrow_forwardGlycine is a diprotic acid, which can potentially undergo two dissociation reactions, one for the a-amino group (-NH3), and the other for the carboxyl (-COOH) group. Therefore, it has two pKą values. The carboxyl group has a pK₁ of 2.34 and the a-amino group has a pK₂ of 9.60. Glycine can exist in fully deprotonated (NH₂-CH₂-COO-), fully protonated (NH3-CH₂-COOH), or zwitterionic form (NH3-CH₂-COO-). Match the pH values with the corresponding form of glycine that would be present in the highest concentration in a solution of th pH. fully deprotonated form NH,−CH,−COO- pH 11.9 pH 6.0 pH 8.0 fully protonated form NH3-CH₂-COOH pH 1.0 Answer Bank pH 7.0 zwitterionic form NH3-CH₂-COO-arrow_forward
- The amino acid His is triprotic with pK1 (α-COOH) = 1.82, pK2 (α-NH3+) = 9.17, and pK3 (side chain) = 6.00. What is the net charge on His at pH 8?arrow_forwardOrnithine is an amino acid that is not used in the synthesis of proteins, but is an important intermediate in several metabloic pathways including the urea cycle and the synthesis of polyamines. It has a perfectly ordinary terminal amino group and terminal carboxyl group like any other amino acid (so use the pKas for those groups given on your amino acids handout), and a side chain with a single ionizable side group with a pKa of 10.3. If ornithine is placed in solution at pH 7.0, it has a net charge of +1. What would the net charge on this amino acid be if the pH of the solution was raised to pH 12.0? Please explain your reasoning.arrow_forward5. Which amino acid listed in the pKa table may behave as a zwitterion at a pH of 7.0-7.4?arrow_forward
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