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What are Peptides?

Below are some notes on peptides that can be used for an understanding or refresher that is helpful and useful for the sciences; specifically biology, chemistry, and biochemistry.

Bonding in Amino Acids: Peptide Bonds

Linking of individual amino acids:

  • formed by covalent bonds
  • bond formed between the alpha-carboxyl group of one amino acid and the alpha-amino group of the next one
  • H2O eliminated in process
  • linked amino acid residues remain after H2O is eliminated

Bonding in this way forms a peptide bond.


Polypeptide chain=the linking of many amino acids

Proteins= made up of polypeptide chains; usually 100+ amino acids.

Amide= another name for a compound formed by the reaction between an amino group and a carboxyl group.

The peptide bond has partial double bond character, and the peptide group that forms the link between the two amino acids is planar.

Peptide bonds are stronger than single bonds because of resonance.

There is no significant rotation around the peptide bond.

What is a Peptide?

A peptide is the compound that is formed when small numbers of amino acids are linked together.

The carbon-nitrogen bond formed when two amino acids are linked together is usually represented as a single bond. A shift in the position of electrons can make this a double bond. This shifting is known as resonance.

The peptide bond can be written as a resonance of two hybrid structures.

There is free rotation around the bonds between the alpha-carbon of a an amino acid residue and the amino and carbonyl carbon of that residue.

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Since there is no free rotation around the peptide bond and since the peptide bond is planar, there is limitation on how a protein backbone can fold in an amino acid; this also affects the three dimensional structure of peptides and proteins.


N-terminal= amino acid residue with the free amino group

C-terminal= amino acid residue with the free carboxyl group

Systemic Nomenclature of Peptides

In the nomenclature of peptides:

  • the N-terminal acid residue is given first
  • the other residues are given in the sequence that they occurC
  • the C-terminal is given last


Dipeptide=the simplest covalently bonded amino acid

Biological Functions of Small Peptides

Small peptides are made up of anywhere from two to several dozen amino acid residues.

Small peptides can have notable physiological effects in organisms.


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Source Information

The information used for this hub was taken from the following sources:

"Biochemistry" by Mary K. Campbell and Shawn O. Farrel; 7th edition.

My biochemistry lectures at school.

Knowledge and notes taken from previous courses in chemistry and biology.

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