Amino acids are the building blocks of peptides. Accordingly, peptides are also referred to as linear chains of amino acids. In order for these peptides to form, a bond must be formed between the individual amino acids and this bond is referred to as a peptide bond.
Basics of peptide bonding
A peptide is an organic chemical compound that consists of a combination of several amino acids. The individual amino acids are connected in a defined order to form a chain. The amino acids of a peptide are in turn linked to one another via a special amide bond. This bond is called a peptide bond.
Peptides are smaller than proteins and are classified systematically based on how many amino acids they are made up of. A distinction is made between oligopeptides and polypeptides, which in turn are divided into subgroups. Oligopeptides are made up of up to ten amino acids, while polypeptides are made up of at least ten amino acids.
Peptides can have different effects in the body. For example, they can have a pain-relieving or anti-inflammatory effect. Therefore, they are often used as an active ingredient in medicines. For example, endorphins are peptides that act as hormones in the body. When these hormones are released in the body, pain is relieved.
In order to understand the structure of the peptide bond, it is important that you repeat the structure of amino acids.
An amino acid consists of a carbon atom to which an amino group (NH3+), a carboxyl group (COOH-) and a residue or side chain are attached.
In a peptide bond, the amino group of the first amino acid now reacts with the carboxyl group of a second amino acid.
as peptide bond is the bond between two amino acids. The linkage is formed with dehydration between the amino group and the carboxyl group. It is also an amide bond.
An amide bond is a bond containing a carbonyl group (CO) that also has a nitrogen atom (N) attached to its carbon atom. A peptide bond is always an amide bond at the same time. However, not every amide bond is a peptide bond. In the case of a peptide bond, the condensation reaction between the terminal carboxyl group of one amino acid and the amino group on the α-carbon atom of a second amino acid must take place.
Formation of a peptide bond
Since the formation of a peptide bond involves the elimination of water, it is a condensation reaction. This is a substitution reaction in which two molecules bond with one another, with the elimination of water. From an energetic point of view, a lot of energy must be applied to form this connection. Nevertheless, this process can be repeated as often as desired, so that very long peptide chains can form.
The simplest amino acid is glycine. Two glycine molecules can react by splitting water to form the dipeptide glycyl-glycine. The carboxyl group of one glycine molecule reacts with the amino group of the second glycine molecule to form a peptide bond.
The formed dipeptide can react back again. This creates two glycine molecules again. This reverse reaction is called hydrolysis. Hydrolysis is a splitting reaction that takes place with the help of water. You will learn more about the cleavage of the peptide bond in the course of this explanation.
Many other forms of the peptide can be formed, such as tripeptides (three amino acids), tetrapeptides (four amino acids), pentapeptides (five amino acids), and so on.
The equilibrium for the formation of a peptide bond is on the side of the free amino acids. This means that energy is required for the biosynthesis of peptide bonds, while their cleavage is thermodynamically voluntary.
Peptide bond resonances
In the peptide bond, the oxygen atom attracts the shared pair of electrons. The reason for this is the difference in electronegativity between the oxygen atom and the carbon atom. The oxygen atom is more electronegative than the carbon atom.
Electronegativity is a measure of how strongly an atom can attract electrons in a chemical bond. Electronegativity is 3.4 for oxygen and 2.6 for carbon.
To ensure that the carbon atom does not lose its four-bond bond, the lone pair of electrons is withdrawn from the adjacent nitrogen atom. This creates a double bond between the nitrogen and the carbon atom for a certain time.
This phenomenon is called partial double bond character. This condition is not permanent and is called mesomerism. This means that the bonding relationships of the molecule can be represented with multiple structures. The actual structure lies between these structures. In the Peptide bond is a so-called planar bond, since the atoms involved lie in one plane.
Because of the double bond character, Distance between the C atom and the N atom less than for a single bond, but still larger than for a true double bond. Normally, single bonds are freely rotatable. In this case, however, this property is lost. Because of this, the resulting proteins always have a specific conformation.
The more mesomeric boundary structures a molecule has, the more stable it is. A peptide bond is therefore a relatively stable bond.
cleavage of the peptide bond
Since peptide bonds are formed by a condensation reaction, they can also be cleaved by their inversion, specifically hydrolysis. Hydrolysis is the splitting reaction of a chemical compound with the help of water. This reaction can be accelerated in several ways:
- Acid or base catalysis can be used to make the bond more reactive.
- The temperature can be increased.
- The enzyme peptidase can be used (peptidases are also sometimes referred to as proteases or proteinases).
Peptide Bonding – The Most Important
- A peptide bond is a bond between the amino group of one amino acid and the carboxyl group of another amino acid. A bond is formed between the carbon atom of the carboxyl group and the nitrogen atom of the amino group.
- Since the formation of a peptide bond involves the elimination of water, it is a condensation reaction.
- A peptide bond is always an amide bond at the same time. However, not every amide bond is a peptide bond.
- Due to electronegativity differences within the peptide bond, creates a double bond character. This condition is not permanent and is called mesomeria designated.
- The reverse of the peptide bond is hydrolysis.
proof
- Cox; Lehninger. (2009). Lehninger Biochemistry. Springer publishing house.
- Voet et al. (2019). Textbook of Biochemistry. Wiley VCH.