Protein Structure
Peptide Bonds
Covalent bonds formed by condensation reactions between amino and carboxyl groups
All amino acids join in the same way, regardless of the R group
Two amino acids joined together is known as a dipeptide
More amino acids joined in a chain are known as a polypeptide
Levels of Protein Structure
Primary structure – the sequence (number and order) of amino acids
Secondary structure – the coiling or folding of an amino acid chain resulting from
hydrogen bonds between different parts of the chain – main forms are an alpha helix or
beta pleated sheet
Tertiary structure – overall 3D shape of a protein molecule
Quaternary structure – protein structure when a protein consists of multiple
polypeptide chains
Other Protein Bonds
Hydrogen bonds – form between hydrogen atoms with a slight positive charge (δ+) and
other atoms with a slight negative charge (δ-) – found in hydroxyl, carboxyl and amino
groups
Ionic bonds – form in R groups where eth amino and carboxyl groups ionise – these are
very strong bonds
Disulfide bridges – string covalent bonds between R groups containing sulfur
Hydrophobic interactions – hydrophobic parts of the R group associate together in the
centre of the polypeptide, away from water
Hydrophilic interactions – hydrophilic parts of the R group are found around the edge of
the polypeptide, close to water
Peptide Bonds
Covalent bonds formed by condensation reactions between amino and carboxyl groups
All amino acids join in the same way, regardless of the R group
Two amino acids joined together is known as a dipeptide
More amino acids joined in a chain are known as a polypeptide
Levels of Protein Structure
Primary structure – the sequence (number and order) of amino acids
Secondary structure – the coiling or folding of an amino acid chain resulting from
hydrogen bonds between different parts of the chain – main forms are an alpha helix or
beta pleated sheet
Tertiary structure – overall 3D shape of a protein molecule
Quaternary structure – protein structure when a protein consists of multiple
polypeptide chains
Other Protein Bonds
Hydrogen bonds – form between hydrogen atoms with a slight positive charge (δ+) and
other atoms with a slight negative charge (δ-) – found in hydroxyl, carboxyl and amino
groups
Ionic bonds – form in R groups where eth amino and carboxyl groups ionise – these are
very strong bonds
Disulfide bridges – string covalent bonds between R groups containing sulfur
Hydrophobic interactions – hydrophobic parts of the R group associate together in the
centre of the polypeptide, away from water
Hydrophilic interactions – hydrophilic parts of the R group are found around the edge of
the polypeptide, close to water
