Definition of a peptide bond

• A peptide bond is formed between two molecules whenever the carboxyl group of one molecule interacts with the amino group of some other molecule to produce a water molecule.
• An isopeptide bond, also defined as a peptide bond, is the amide bond which forms between the carboxyl group of one amino acid and also the amino group of another amino acid at positions other than the alpha position.
• One instance of a condensation event that results in dehydration is the process of peptide bond synthesis (removal of water).
• Any two amino acids can form peptide bonds, which are covalent bonds, to form a peptide chain.
• The incomplete double bond between carbon as well as nitrogen in the amide bond stabilises the peptide bond.
• The carbonyl group receives a lone pair donation from the nitrogen, which is a component of the bond, creating a resonance effect.
• Since electrons may be delocalized over several atoms to create a resonance structure, the resonance is extremely stable.
• As a result, the partial double bond in the resonance structure inhibits rotation of the amide bond while simultaneously stabilising the bond.
• The peptide bonds around the C-N bond have a planar shape that rotates minimally, but the single bonds on either side of the C-N bond rotate significantly.

What is a peptide?

• A protein is made up of many peptides, each of which is a short chain of amino acids.
• A peptide may have anywhere between two and fifty amino acids.
• Peptides come in a variety of forms depending on how many amino acids they include. Peptides with ten amino acids or less are known as oligopeptides, while those with more than ten are known as polypeptides.
• Then, proteins are polypeptides with about 100 amino acids.

Peptide bond formation mechanism

• The process of dehydration synthesis is the mechanism for the formation of peptide bonds.
• In the formation of a peptide bond, the carboxyl group of one amino acid goes toward the amino group of the other amino acid.
• The carboxyl group (COOH) of the initial amino acid subsequently eliminates one hydrogen and an oxygen atom. In contrast, the other amino acid’s amino group (NH2) loses one hydrogen.
• As a result, a water molecule (H2O) is released, and a C-N amide bond is created between the two amino acids.
• The formation of a peptide bond between two amino acids results in the formation of a dipeptide molecule.
• Therefore, a peptide bond is formed while the carboxyl group of one amino acid condenses with the amino group of another amino acid, yielding a water molecule.
• An endergonic reaction, the creation of peptide bonds, requires energy, which in living things comes from ATP.
• Dehydration synthesis reaction is the name given to this reaction because it includes the elimination of a water molecule.

Peptide bond degradation mechanism

• Hydrolysis, the process that breaks down the peptide link, necessitates the presence of water molecules.
• A partial double bond maintains the amide connection between the amino acids, which causes the degradation process to proceed very slowly.
• The carbon atom produces a little positive charge as a result of the partial double bond that exists between the nitrogen molecule and carbon.
• The peptide bond breaks down when water is present because the OH-ions in the water assault the carbon atom.
• The amino group is created when the leftover hydrogen ion from the water hits the nitrogen atom.
• This results in the peptide molecule separating into two units, one containing an amino group and the other containing a carboxyl group.
• An exergonic process called peptide degradation produces 8–16 Kjol/mole of energy.
• Proteolytic enzymes such as proteases as well as peptidases often catalyse protein breakdown events since they are so sluggish.

Peptide bond hydrolysis

• All protein hydrolysis processes begin with the hydrolysis of peptide bonds.
• The peptide bond is hydrolyzed by acid, which is the most typical route of protein disintegration.
• Peptide hydrolysis is essential in some synthetic techniques in which amino acids from one peptide are split and moved to another peptide, resulting in different peptide synthesis.
• Similar to how various peptides and proteins build up in cells, toxicity results. These poisons must also be removed via peptide bond hydrolysis.
• Peptide bond hydrolysis is a critical step in the digestion of proteins in biological organisms.
• Hydrolysis of the peptide bond occurs when water and acid are present.
• One method of peptide bond degradation known as peptide bond hydrolysis involves the cleavage of polypeptides into smaller peptides or the breakdown of smaller peptides into individual amino acids.

Examples

All proteins have the peptide bond, which holds the amino acids in the chain together.

Possessing only one amino acid, a monopeptide

Having two amino acids, a dipeptide

Three amino acids make up a tripeptide.

Tetrapeptide: a four-amino-acid molecule

Having five amino acids, a pentapeptide

Having six amino acids, hexapeptide

Seven amino acids make up a heptapeptide.

An octapeptide has eight amino acids.

Revision Questions/FAQs

What is a peptide bond?

A peptide bond is a special type of amide bond formed between two molecules where an α-carboxyl group of one molecule reacts with the α-amino group of another molecule releasing a water molecule.

Which parts of amino acids are involved in a peptide bond?

The carboxyl group of one amino acid and the amino group of another amino acid are involved in a peptide bond.

How do you identify a peptide bond?

Biuret test can be used to identify a peptide bond.

Is a peptide bond covalent?

Yes, a peptide bond is a covalent bond.

References

• Jain JL, Jain S, and Jain N (2005). Fundamentals of Biochemistry. S. Chand and Company.
• Nelson DL and Cox MM. Lehninger Principles of Biochemistry. Fourth Edition.
• Berg JM et al. (2012) Biochemistry. Seventh Edition. W. H Freeman and Company.
• ARLINGHAUS R, SHAEFER J, SCHWEET R. MECHANISM OF PEPTIDE BOND FORMATION IN POLYPEPTIDE SYNTHESIS. Proc Natl Acad Sci U S A. 1964; 51(6):1291-1299. DOI:10.1073/pnas.51.6.1291

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