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
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