Concept explainers
An octapeptide contains the following amino acids: Arg, Glu, His, Ile, Leu, Phe, Tyr, and Val. Carboxy peptidase treatment of the octapeptide forms Phe and a heptapeptide. Treatment of the octapeptide with chymotrypsin forms two tetrapeptides,
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Chapter 29 Solutions
Organic Chemistry
- For the tripeptide GlyAlaCys a. What amino acid is located at the peptides N-terminal end? b. What amino acid is located at the peptides C-terminal end? c. How many peptide bonds are present? d. How many amide linkages are present?arrow_forwardA chemically modified guanidino group is present in cimetidine (Tagamet), a widely prescribed drug for the control of gastric acidity and peptic ulcers. Cimetidine reduces gastric acid secretion by inhibiting the interaction of histamine with gastric H2 receptors. In the development of this drug, a cyano group was added to the substituted guanidino group to alter its basicity. Do you expect this modified guanidino group to be more basic or less basic than the guanidino group of arginine? Explain.arrow_forwardFor the tripeptide SerValMet a. What amino acid is located at the peptides N-terminal end? b. What amino acid is located at the peptides C-terminal end? c. How many peptide bonds are present? d. How many amide linkages are present?arrow_forward
- 22-47 How many different tetrapeptides can be made (a) if the peptides contain the residues of asparagine, proline, serine, and metbionine and (b) if all 20 amino acids can be used?arrow_forwardA 1.00-mg sample of a pure protein yielded on hydrolysis 0.0165 mg of leucine and 0.0248 mg of isoleucine. What is the minimum possible molar mass of the protein? (MMleucine=MMisoleucine=131g/mol)arrow_forwardThe dynorphins are a group of opioid peptides that play an importantrole in changes in the brain associated with cocaine addiction. One ofthese peptides, dynorphin A, contains the following amino acidsequence: Tyr–Gly–Gly–Phe–Leu–Arg–Arg–Ile–Arg–Pro–Lys–Leu–Lys.Draw the amino acids and peptide fragments formed when dynorphin A is treated with each reagent or enzyme: (a) chymotrypsin; (b) trypsin; (c)carboxypeptidase; (d) C6H5N=C=S.arrow_forward
- Draw the structure of leu-enkephalin, a pentapeptide that acts as an analgesic and opiate, and has the following sequence: Tyr–Gly–Gly–Phe–Leu. (The structure of a related peptide, met-enkephalin, appeared in Section 22.6B.)arrow_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_forwardDetermine the primary structure of an octapeptide from the following data: Acid-catalyzed hydrolysis gives 2 Arg, Leu, Lys, Met, Phe, Ser, and Tyr. Carboxypeptidase A releases Ser. Edman’s reagent releases Leu. Treatment with cyanogen bromide forms two peptides with the following amino acid compositions: 1. Arg, Phe, Ser 2. Arg, Leu, Lys, Met, Tyr Trypsin-catalyzed hydrolysis forms the following two amino acids and two peptides: 1. Arg 2. Ser 3. Arg, Met, Phe 4. Leu, Lys, Tyrarrow_forward
- Hydrolysis of decapeptide P with the enzyme trypsin affords the following fragments: Gly-Asp, Ala-Cys-Lys, Leu-Trp- Val-Gly-Arg. Hydrolysis with chymotrypsin yields: Leu-Trp, Val-Gly-Arg-Ala-Cys-Lys-Gly-Asp. What is the amino acid sequence of P?arrow_forwardA peptide has the sequence Glu–His–Trp–Ser–Gly–Leu–Arg–Pro–Gly The p?a values for the peptide’s side chains, terminal amino groups, and carboxyl groups are provided in the table. Amino acid Amino pKa Carboxyl pKa Side‑chain pKa glutamate 9.609.60 2.342.34 4.254.25 histidine 9.179.17 1.821.82 6.006.00 tryptophan 9.399.39 2.382.38 serine 9.159.15 2.212.21 glycine 9.609.60 2.342.34 leucine 9.609.60 2.362.36 arginine 9.049.04 2.172.17 12.4812.48 proline 10.9610.96 1.991.99 Calculate the net charge of the molecule at pH 11 and estimate the isoelectric point (pI)(pI) for this peptide.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_forward
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