Peptide bond

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Peptide Bond Formation.jpg

Peptide bonds (also known as amide bonds[1]) are the bonds that are found between two monomer units of amino acids in a polypeptide chain. They are created through condensation reactions in which a molecule of water (H2O) is removed. The water is made by combining a hydroxyl group (OH) of one amino acid with a hydrogen from the amino group (NH2). The two amino acids then become linked by a new peptide bond and is called a dipeptide. Polypeptide chains are made up of amino acids linked together by these peptide bonds and this linear sequence forms the primary structure of a protein. The formation of a peptide bond occurs during protein synthesis whereby which ribosomes (consisting of one small subunit and one large subunit) translate an mRNA sequence coding for the protein (translation).

The peptide bond is a stable covalent bond and is said to be a rigid planar bond because it has a partial double bond character. The evidence that shows this partial double bond character is from the length of the bond. It is 0.13 Angstrom shorter than the C-N single bond yet not as short as a double bond[2].

Peptide bonds can also be easily broken by hydolysis (amide hydrolysis). This is completely the opposite to condensation, whereby water is added to the dipeptide/polypeptide and the peptide bond breaks to give its two constituent amino acids.

A peptide bond is a kind of linkage between two amino acids. It is also known as an amide bond. A peptide bond connects two amino acids, forming a dipeptide, and is associated with the loss of a water molecule. This process is called a condensation reaction. One perhaps surprising fact about peptide bonds is that they are very kinetically stable, in fact, a peptide bond in a solution will last 1000 years if no catalyst is present to disrupt it.

Many amino acids can be connected via peptide bonds, making a polypeptide. Each amino acid is then called a residue as it forms part of the polypeptide[3]. The ends of a polypeptide chain will be different because an alpha amino group is present at one end and an alpha carboxyl group present at the other. This gives the polypeptide chain polarity[4].


  1. Berg,JM.Tymoczko, JL.and Stryer, L.,2007.Biochemistry. 6th Edition. New York: Sara Tenney.
  2. Voet, Voet, Pratt (2008) Principles of Biochemistry, 3rd Ed. Wiley. 127
  3. Berg, Tymoczko, Stryer, Biochemistry 6th ed, W.H. Freeman and Company, 2007
  4. Alberts, Johnson, Lewis, Raff, Roberts, Walter. Molecular Biology of The Cell 2008, Garland Science.
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