Complete hydrolysis of a 100.00-g sample of a peptide gave...

Complete hydrolysis of a 100.00-g sample of a peptide gave the following amounts of individual amino acids (molar masses, in g/mol, appear in parentheses): $$ \begin{array}{ll}{3.00 \mathrm{g} \text { of glycine }(75.07)} & {0.90 \mathrm{g} \text { of alanine }(89.10)} \\ {3.70 \mathrm{g} \text { of valine }(117.15)} & {6.90 \mathrm{g} \text { of proline }(115.13)} \\ {7.30 \mathrm{g} \text { of serine }(105.10)} & {86.00 \mathrm{g} \text { of arginine }(174.21)}\end{array} $$ (a) Why does the total mass of amino acids exceed the mass of peptide? (b) What are the relative numbers of amino acids in the peptide? (c) What is the minimum molar mass of the peptide?

Complete hydrolysis of a 100.00-g sample of a peptide gave the following amounts of individual amino acids (molar masses, in g/mol, appear in parentheses):
$$
\begin{array}{ll}{3.00 \mathrm{g} \text { of glycine }(75.07)} & {0.90 \mathrm{g} \text { of alanine }(89.10)} \\ {3.70 \mathrm{g} \text { of valine }(117.15)} & {6.90 \mathrm{g} \text { of proline }(115.13)} \\ {7.30 \mathrm{g} \text { of serine }(105.10)} & {86.00 \mathrm{g} \text { of arginine }(174.21)}\end{array}
$$
(a) Why does the total mass of amino acids exceed the mass of peptide? (b) What are the relative numbers of amino acids in the peptide? (c) What is the minimum molar mass of the peptide?

Key Concepts

Peptide Bond Hydrolysis

This concept refers to the reaction in which peptide bonds, which link amino acids in proteins or peptides, are broken by the addition of water during a hydrolysis reaction. In a complete hydrolysis, every peptide bond is cleaved, yielding free amino acids. The process is used to analyze protein composition and structure by identifying the resulting amino acids.

Dehydration Synthesis (Condensation Reaction)

In biological systems, proteins and peptides are formed by linking amino acids through a dehydration synthesis reaction, also known as a condensation reaction, where each peptide bond formation results in the loss of a water molecule. This idea is crucial because it explains why the total mass of amino acids obtained upon hydrolysis exceeds the mass of the original peptide, as the calculation needs to account for the water molecules that were removed during synthesis.

Stoichiometric Analysis in Biochemistry

Stoichiometry in biochemistry involves the quantitative relationship between reactants and products in chemical reactions, such as the hydrolysis of peptides. It is used to determine the relative molar ratios of amino acids in a peptide by converting the masses of each amino acid obtained after hydrolysis into moles and then comparing these values to deduce the sequence or composition.

Molar Mass Calculations and Molecular Weight Estimation

This concept deals with calculating the molecular weight of biomolecules based on the sum of the molar masses of their constituent units, while also considering changes that occur during synthesis (e.g., loss of water). Estimating the minimum molar mass of a peptide requires accounting for both the mass of the amino acid residues and the water molecules removed during peptide bond formation.

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