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Chapter 24: Q18P. (page 1276)

Draw the complete structures of the following peptides:

(a) Thr-Phe-Met (b) Serylarginylglycylphenylalanine (c) IMQDK (d) ELVIS

Short Answer

Expert verified

(a)

Structure of the peptide Thr-Phe-Met

(b)

Structure of the peptide seryl-arginyl-glycyl-phenylalanine

(c)

Structure of the peptide IMQDK

(d)

Structure of the peptide ELVIS

Step by step solution

01

Peptide bond formation

The amides obtained by the interaction between the amino and carboxylic groups of two or more amino acid molecules are known as peptides. The amide group -CO-NH- in the peptides is known as a peptide linkage.

02

Structures of the peptide

(a)

The complete structure of the peptide Thr-Phe-Met is shown in the figure below:

Structure of the peptide Thr-Phe-Met

(b)

The complete structure of the peptide seryl-arginyl-glycyl-phenylalanine is shown in the figure below:

Structure of the peptide seryl-arginyl-glycyl-phenylalanine

(c)

The complete structure of the peptide IMQDK (isoleucine-methionine-glutamine-aspartate-lysine) is shown in the figure below:

Structure of the peptide IMQDK

(d)

The complete structure of the peptide ELVIS (glutamic acid-leucine-valine-isoleucine-serine) is shown in the figure below:

Structure of the peptide ELVIS

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Most popular questions from this chapter

Histidine is an important catalytic residue found at the active sites of many enzymes. In many cases, histidine appears to remove protons or to transfer protons from one location to another.

(a) Show which nitrogen atom of the histidine heterocycle is basic and which is not.

(b) Use resonance forms to show why the protonated form of histidine is a particularly stable cation.

(c) Show the structure that results when histidine accepts a proton on the basic nitrogen of the heterocycle and then is deprotonated on the other heterocyclic nitrogen. Explain how histidine might function as a pipeline to transfer protons between sites within an enzyme and its substrate.

The Sanger method for N-terminus determination is a less common alternative to the Edman degradation. In the Sanger method, the peptide is treated with the Sanger reagent, 2,4-dinitrofluorobenzene, and then hydrolyzed by reaction with 6 M aqueous HCl. The N-terminal amino acid is recovered as its 2,4-dinitrophenyl derivative and identified.

(a)Propose a mechanism for the reaction of the N terminus of the peptide with 2,4-dinitrofluorobenzene.

(b) Explain why the Edman degradation is usually preferred over the Sanger method.

Show how the following amino acids might be formed in the laboratory by reductive amination of the appropriate α-ketoacid.

Phenylalanine (b) Cysteine (c) Serine (d) Alanine

The herbicide glyphosate(Roundup) kills plants by inhibiting an enzyme needed for synthesis of phenylalanine. Deprived of phenylalanine, the plant cannot make the proteins it needs, and it gradually weakens and dies. Although a small amount of glyphosate is deadly to a plant, its human toxicity is quite low. Suggest why this powerful herbicide has little effect on humans.

Most naturally occurring amino acids have chiral centers (the asymmetric α carbon atoms) that are named (S) by the Cahn-Ingold-Prelog convention (Section 5-3). The common naturally occurring form of cysteine has a chiral center that is named (R), however.

(a) What is the relationship between (R)-Cysteine and (S)-alanine? Do they have the opposite three-dimensional configuration (as the names might suggest) or the same configuration?

(b) (S)-Alanine is an L-amino acid (Figure 24-2). Is (R)-cysteine a D-amino acid or an L-amino acid?
See all solutions

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