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Vincenzo Fogliano » 3.Amino acids and peptide bond


Amino acids and peptide bond

Amino acids (AAS) are formed by a central carbon named carbon alpha linked to an amino group and a corboxyl acid group.

They differ from the R group.

Amino acids are classified according to the R nature.


Amino acids and peptide bond

All natural AAS have “L”stereochemistry.

Non natural AAS have “D” stereochemistry.

The main features of AAS due to the characteristics of lateral chain (R) are the molecular weight and the isoelectric point.

Amino acids and peptide bond

  • AA with alkyl group
  • AA with hydroxyl group
  • AA with S atom
  • Basic AA
  • Acid AA
  • Amidic AA
  • AA with an aromatic ring

Isoelectric point

Is the pH value at which an amino acid has a total charge equal to zero.

This means balance between positive and negative charges.


Isoelectric point


Peptide bond between two amino acids

Peptides -> Polipeptides ->  Proteins

Peptides -> Polipeptides -> Proteins


Peptide bond between two amino acids

Peptide bonds are very strong.
Explain why!

Peptide bonds are very strong. Explain why!


Peptide bond between two amino acids


Peptide bond between two amino acids

φ e Ψ  angles can rotate.

φ e Ψ angles can rotate.


Peptide bond between two amino acids


Peptide bond between two amino acids

Rotation around the plane of the peptide bond mainly depends on the steric hindrance of the R group.


Polypeptide chain


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