Peptide Bond Formation and Hydrolysis


MCAT Biochemistry

In the world of proteins, amino acids are linked together by peptide bonds. A peptide is a short chain of amino acids containing between two and fifty amino acids. When two amino acids bind through a process called dehydration synthesis, a peptide bond is formed. Dehydration synthesis is a nucleophilic substitution reaction between the amino group of one amino acid and the carboxyl group of the other, with water as a leaving group. These reactions are also known as condensation reactions.

Peptide bonds are broken through a process called hydrolysis, which involves the addition of a water molecule. In living organisms, this process is catalyzed by hydrolase enzymes. When the peptide bond breaks, the OH from the water molecule binds to the carbonyl, forming a carboxyl group, and the amide nitrogen binds to the hydrogen from the water or picks it up from the surrounding solution to form an amine. Proteins are fundamentally long peptide chains of amino acids with N- and C-terminals that are linked together through dehydration synthesis and broken apart using hydrolysis.

Lesson Outline

<ul> <li>Introduction to Peptide Bonds and Amino Acids</li> <ul> <li>Amino acids are linked by peptide bonds</li> <li>Proteins consist of multiple polypeptide chains (hundreds or thousands of amino acids); peptides are shorter</li> <li>Peptides are named based on the number of amino acids linked together (dipeptide, oligopeptide, etc.)</li> <li>Peptides have an N-terminus and a C-terminus</li> </ul> <li>Peptide Structure and Formation</li> <ul> <li>Peptide bonds are covalent bonds between carbonyl and amino groups</li> <li>Formed through dehydration synthesis, a nucleophilic substitution reaction</li> <li>Dehydration synthesis is also called a condensation reaction</li> </ul> <li>Breaking Peptide Bonds: Hydrolysis</li> <ul> <li>Peptide bonds are broken by the addition of a water molecule</li> <li>Hydrolysis is a process involving the use of water to break bonds</li> <li>In living organisms, hydrolase enzymes catalyze the process</li> <li>Broken peptide bonds result in unbonded amino acids</li> </ul> </ul>

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What is a peptide bond and how does it form between amino acids?

A peptide bond is a covalent chemical bond that forms between the carboxyl group of one amino acid and the amino group of another amino acid. This bond forms through a dehydration synthesis reaction, also known as a condensation reaction, in which a water molecule is removed. The resulting linkage between the two amino acids creates a dipeptide, and this process can be repeated to form polypeptides and proteins.

What is the difference between oligopeptides and polypeptides?

Oligopeptides and polypeptides refer to chains of amino acids linked through peptide bonds. The main difference between them lies in the number of amino acids in the chain. Oligopeptides generally consist of a small number of amino acids, typically between 2 and 20. Polypeptides, on the other hand, consist of longer chains containing 21 or more amino acids. If a polypeptide chain is folded and structured into a functional unit, it becomes a protein.

How are the N-terminus and C-terminus related to peptide bond formation?

The N-terminus and C-terminus are the two ends of a peptide or protein chain. The N-terminus refers to the nitrogen-containing end of the peptide, specifically the amino end (NH2) of the first amino acid in the chain. The C-terminus refers to the carbon-containing end of the peptide, specifically the carboxyl end (COOH) of the last amino acid in the chain. The peptide bond is formed between the N-terminus of one amino acid and the C-terminus of another amino acid.

What is the process of hydrolysis in the context of peptide bonds?

Hydrolysis is a chemical process in which a peptide bond is broken down by adding a water molecule. The reaction is essentially the reverse of the dehydration synthesis that forms peptide bonds. Hydrolysis of peptide bonds occurs in the presence of hydrolase enzymes, which catalyze the reaction by facilitating the nucleophilic substitution and promoting the breakage of the bond. As a result, the polypeptide chain is broken into smaller peptides or individual amino acids.

What roles do hydrolase enzymes play in peptide bond hydrolysis?

Hydrolase enzymes are responsible for catalyzing the hydrolysis reaction, which breaks down peptide bonds. They work by facilitating nucleophilic substitution, in which the hydroxyl group from the added water molecule attacks the carbonyl carbon atom in the peptide bond. The enzymes effectively lower the activation energy required for the reaction, making it more favorable and allowing the peptide bond to be broken apart, resulting in smaller peptide chains or individual amino acids.