Concept explainers
(a)
Interpretation:
The explanation for iodoacetic acid reaction with side chain thiol group of a cysteine residue is to be stated. The reason as to why this reaction is necessary before sequencing is to be stated.
Concept introduction:
The reagent DTT is known as dithiothreitol and is a common redox reagent. It is also known as Cleland’s reagent. It is relatively not a stable compound due to air oxidation. It is used as a deprotecting group and to break the disulfide bond in protein.
(b)
Interpretation:
The product obtained on oxidation of disulfide bond with
Concept introduction:
The compound hydrogen peroxide represented by
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EBK ORGANIC CHEMISTRY
- (a) Redraw the tripeptide in zwitterionic form (b) Explain how ESI-MS can be used to determine which amino acid is in the middle of the sequence.arrow_forwardQ1)In the pH range 1.82 to 8.99, H2Arg+ is the principal form of arginine. Which is the second most prominent species at pH 6.0? At pH 5.0?Q2) (a) Draw the structure of the predominant form (principal species) of 1,3-dihydroxybenzene at pH 9.00 and at pH 11.00.(b) What is the second most prominent species at each pH?(c) Calculate the percentage in the major form at each pHarrow_forwardindicate the RIGHT alternative: (a) The Zwitterion form of an amino acid exists only at a point pH value. (b) In a peptide bond there is free rotation at the C-N bond. (c) In a polypeptide, the terminal carboxyl group may be present in its amide form. (d) At a pH greater than pI, an amino acid tends to move towards the cathode in an electrophoresis. (e) At any pH below pI, the predominant form of an amino acid is negatively charged.arrow_forward
- The pKa of the conjugate acid of guanidine is 13.6, making it one of the strongest neutral organic bases. Offer an explanation.arrow_forward(b) Using alanine as an example, draw possible conformations of alanine in a peptide chain and identify which conformer is favoured. (c) Discuss how considering 'allylic strain' [see pages 33-39 of handout 1] can explain the favoured conformation in part b above, and how this is relevant to the B-sheet conformation in peptides/proteins.arrow_forwardAt very low pH, alanine is a diprotic acid that can be represented as H3N1-CH(CH3)-COOH. The pKa of the carboxyl group is 2.3, and the pKa of the UNH1 3 group is 9.7.(a) At pH 7, what fraction of the amino acid molecules dissolved in an aqueous solution will have the form H3N1-CH(CH3)-COO2?(b) What fraction of the molecules at this pH will havethe form H2N-CH(CH3)-COOH?arrow_forward
- A tripeptide contains lysine (R= -(CH₂)4NH₂), phenylalanine (R= -CH₂C6H5) and glycine (R= -H). It was found that the tripeptide reacts with 2 moles of DNFB to give compound A. When compound A was treated with SOCI2, glycine was activated. When hydrolyzed, both NH₂ groups of lysine were found to be DNP-labelled. What is the structure of the tripeptide? Select one: H (CH₂)2NH2 CH NH CH H₂N O O H₂N H₂N H₂N C (CH2)4NH2 CH 010 (CH2)4NH2 CH C=O CH,Ph CH NH NH NH CH CH,Ph CH H 010 CH CH,Ph CH (CH2)4NH2 ΝΗ NH NH NH CH,Ph CH H CH COOH H CH COOH COOH COOHarrow_forward(a) Draw a structural formula for the products formed when alanine is treated with the following reagents. (i) (Boc)20, NaOH (ii) CbzCI, NazCO3 (iii) 2-Methylpropene, p-TSOH (b) Enfuvirtide, a 36-amino-acid peptide drug, was manufactured at a multi-tonne per year scale. The manufacture relied on solid phase synthesis with Barlos resin as the solid support. Part of the solid phase synthesis is shown below. Write the structure of the product A and discuss the cleavage mechaniśm of the peptide from the resin. 1. Fmoc-Leu-OH, DIPEA 2. 20% piperidine in DMF 3. Fmoc-Glu('Bu)-OH, HBTU, HOBt 4. 20% piperidine in DMF 5. Fmoc-Leu-OH, HBTU, HOBT 6. 20% piperidine in DMF 7. Fmoc-Leu-OH, HBTU, HOBE 8. 20% piperidine in DMF 9. 10% HOAC in CH2CI2 Barlos resinarrow_forward(b) Describe how the charge of some amino groups in a protein might differ at pH 9.0 and pH 5.0. the charge on the amino group will differ at pH 5 and pH 9 which will depend on the pKa of the amino acid. (c) Describe how the charge of some carboxyl groups in a protein might differ at pH 9.0 and pH 5.0. charge on carboxyl group will differ at pH 5 and pH 9 which will depend on the pKa of the amino acid. (d) Given your answers to parts (b) and (c), what kind of intramolecular interactions in beta-galactosidase are most likely to be affected by a change in pH from 9.0 to 5.0? (e) Could the interactions you mention in part (d) affect the catalytic activity of beta-galactosidase?arrow_forward
- The peptide Proline-Serine-Alanine-Phenylalanine-Glutamine is present at pH 7. Draw the peptide and include stereochemistry.arrow_forwardTaking the structure of the amino acids into account, give a comparative discussion of these pK values : Alanine : 2.34 : 6.1 : 9.70 Histidine: 1.82 : 9.17arrow_forwardExplain what is meant by the following :(i) peptide linkage(ii) pyranose structure of glucosearrow_forward