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Chapter 27: Problem 23

Draw a structural formula for the form of each amino acid most prevalent at pH \(1.0\). (a) Threonine (b) Arginine (c) Methionine (d) Tyrosine

Short Answer

Expert verified
Answer: (a) Threonine: H3N+-CH-COOH | CH-CH3 | OH (b) Arginine: H3N+-CH-COOH | CH2-CH2-CH2-CH2-NH-C(NH2+)NH2 (c) Methionine: H3N+-CH-COOH | CH2-CH2-S-CH3 (d) Tyrosine: H3N+-CH-COOH | CH2-C6H4-OH

Step by step solution

01

(a) Threonine

Threonine has the following structure in its non-ionized form: H2N-CH-COOH | CH-CH3 | OH At pH 1, the carboxyl group (-COOH) and amino group (-NH2) will be protonated. The side chain of Threonine has a hydroxyl (-OH) group, which generally does not protonate at pH 1. The protonated structure of Threonine is: H3N+-CH-COOH | CH-CH3 | OH
02

(b) Arginine

Arginine has the following structure in its non-ionized form: H2N-CH-COOH | CH2-CH2-CH2-CH2-NH-C(NH)NH2 At pH 1, the carboxyl group (-COOH), amino group (-NH2), and guanidinium (-C(NH)NH2) will be protonated. The protonated structure of Arginine is: H3N+-CH-COOH | CH2-CH2-CH2-CH2-NH-C(NH2+)NH2
03

(c) Methionine

Methionine has the following structure in its non-ionized form: H2N-CH-COOH | CH2-CH2-S-CH3 At pH 1, the carboxyl group (-COOH) and amino group (-NH2) will be protonated. However, the sulfur atom in Methionine does not carry a charge and will not be protonated. The protonated structure of Methionine is: H3N+-CH-COOH | CH2-CH2-S-CH3
04

(d) Tyrosine

Tyrosine has the following structure in its non-ionized form: H2N-CH-COOH | CH2-C6H4-OH At pH 1, the carboxyl group (-COOH) and amino group (-NH2) will be protonated. The phenolic hydroxyl group (-OH) on the ring of Tyrosine can also be protonated due to its acidic nature, but it generally has a pKa of around 10, which is higher than the pH 1 given, so it remains non-ionized. The protonated structure of Tyrosine is: H3N+-CH-COOH | CH2-C6H4-OH

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Most popular questions from this chapter

For lysine and arginine, the isoelectric point, pI, occurs at a pH where the net charge on the nitrogen-containing groups is \(+1\) and balances the charge of \(-1\) on the \(\alpha\)-carboxyl group. Calculate pI for these amino acids.

Several \(\beta\)-amino acids exist. There is a unit of \(\beta\)-alanine, for example, contained within the structure of coenzyme A (Problem 25.35). Write the structural formula of \(\beta\)-alanine.

Both norepinephrine and epinephrine are synthesized from the same protein- derived amino acid. From which amino acid are they synthesized, and what types of reactions are involved in their biosynthesis? a. b.

Examine the \(\alpha\)-helix conformation. Are amino acid side chains arranged all inside the helix, all outside the helix, or randomly?

Draw a structural formula of these tripeptides. Mark each peptide bond, the \(N\)-terminal amino acid, and the G-terminal amino acid. (a) Phe-Val-Asn (b) Leu-Val-Gln
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