1-3-1-amino-acids-and-the-peptide-bond

Amino acids & the peptide bond

Proteins

• Proteins are polymers (and macromolecules) made of monomers called amino acids

• The sequence, type and number of the amino acids within a protein determine its shape and therefore its function

• Proteins are essential in cells because they form all of the following:

  • Enzymes

  • Cell membrane proteins (e.g. carrier)

  • Hormones

  • Immunoproteins (e.g. immunoglobulins)

  • Transport proteins (e.g. haemoglobin)

  • Structural proteins (e.g. keratin, collagen)

  • Contractile proteins (e.g. myosin)

Amino acids

• Amino acids are the monomers of proteins

• There are 20 amino acids found in proteins common to all living organisms

• The general structure of all amino acids is a central carbon atom bonded to:

  • an amine group -NH₂

  • a carboxylic acid group -COOH

  • a hydrogen atom

  • an R group (which is how each amino acid differs and why amino acid properties differ, e.g. whether they are acidic or basic or whether they are polar or non-polar)

Peptide bond

• To form a peptide bond, a hydroxyl (-OH) is lost from the carboxylic group of one amino acid, and a hydrogen atom is lost from the amine group of another amino acid

• The remaining carbon atom (with the double-bonded oxygen) from the first amino acid bonds to the nitrogen atom of the second amino acid

• This is a condensation reaction, so water is released

• Dipeptides are formed by the condensation of two amino acids

• Polypeptides are formed by the condensation of many (three or more) amino acids

• A protein may have only one polypeptide chain, or it may have multiple chains interacting with each other

• During hydrolysis reactions, the addition of water breaks the peptide bonds, resulting in polypeptides being broken down to amino acids