What is a peptide bond?

Peptide bond

It is important to remember that amino acids have the ability to covalently join in a condensation reaction to form a dipeptide and water . The covalent bond that occurs between amino acids is called a peptide bond , and for this reason, long chains of covalently linked amino acids are called polypeptides . Polypeptide chains can be broken down through hydrolysis reactions , which require water to reverse the process.  

What is a peptide bond?

It is a chemical bond that occurs between the carboxyl group of an amino acid and the amino group of another amino acid, losing a water molecule to give rise to peptides and proteins .

Peptide bonds are an important part of the primary structure of a protein which is defined as the amino acid sequence of which it is composed. This sequence is what determines the shape that the protein will take, according to the spatial limitations in the arrangement of the atoms in the protein, the chemical properties of the component amino acid residues and the environment of the protein.

The peptide bonds that are responsible for joining the amino acid residues in a polypeptide are formed through a condensation reaction between the acidic carboxyl group of one amino acid and the basic amino group of another amino acid. In the context of a peptide, the amide group (CO-NH) is called a peptide group.

  • Peptide bond characteristics
  • How a peptide bond is formed
  • Properties
  • Examples of peptide bond

Peptide bond characteristics

The main characteristics that peptide bonds have are the following:

  • The peptide bond is shorter than a normal single bond.
  • It has 60% double bond and is stabilized by resonance.
  • No free spins are found on this type of link.
  • It is a covalent bond between the amino group of one amino acid and the carboxyl group of another amino acid.
  • The CN bond that is found joining two amino acids is shorter than other CN bonds.
  • The four atoms of the bond are in the same plane, with oxygen and nitrogen in the trans position.
  • The six atoms involved in the formation of the peptide bond are contained in it
  • The peptide bond has higher polarity and has a dipole moment.
  • Each peptide bond can become involved in two hydrogen bonds.
  • When three amino acids are joined, a tripeptide will be formed , and more are joined, tetra peptides , oligopeptides and polypeptides are formed .

How a peptide bond is formed

To understand the way in which a peptide bond originates, it is important to mention beforehand the structure that an amino acid has . Amino acids are monomers , they have an amino group (basic) at one end and a carboxyl group (acid) at the other , which allows them to have a series of very important properties. A peptide bond is made up of the union of a carboxyl group of one amino acid and the amino group of the next.

In the formation of the peptide bond, the carboxyl of an amino acid participates, which reacts with the amino group of another amino acid and thus produces the formation of a water molecule , making the amino acids become united. The structure that results from this union is known as a dipeptide . If you add another amino acid to this dipeptide, you will have a tripeptide , and so on. This is the way obtainable becoming larger molecules, which are called generally of peptides . When about 50 amino acids have been attached, then a protein will be formed .


The properties of peptide bonds are as follows:

  • Conformation: it is each of the three-dimensional arrangements that the atoms that a peptide has can adopt, filing all its covalent bonds. Of all the possible ones, only a few occur under physiological conditions. A conformation can be stabilized through the interactions that occur between the groups that form it, such as hydrogen bonds and disulfide bonds, and with the solvent .
  • Peptide bonds have a polar character , this because oxygen is more electronegative than hydrogen and for this reason it attracts electrons that are shared, giving rise to an uneven distribution of electrons that are delocalized. Oxygen has a charge that is partially negative and hydrogen has a charge that is partially positive.
  • The peptide bond is flat and the partial double bond character prevents free rotation in the amino bond, placing the six atoms of the peptide group in the same plane.
  • Peptide bonds can also be degraded or broken through hydrolysis , the process during which water is added, thus releasing an amount of energy in a tremendously slow process. This can be accelerated in the presence of acidic, basic or enzymatic catalysts.

Examples of peptide bond

Some examples of peptide bonds are mentioned below:

  • Bradykinin : it is a compound made up of nine amino acids, this peptide is a drug that produces vasodilation and a drop in blood pressure, used in arterial hypertension .
  • Oxytocin : is a hormone produced by the hypothalamus that regulates the central nervous system and participates in the preparation of the female cervix during childbirth and of the breasts during lactation .
  • Insulin : it is a polypeptide hormone made up of 51 amino acids that regulates the blood sugar cycle.
  • Prolactin : stimulates the production of milk in the maternal breasts. It is made up of a sequence of 198 amino acids.

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