– A conjugated protein
– Red, oxygen carrying pigment in red blood cells
– A quaternary protein made from four polypeptides – 2 alpha and 2 beta subunits
– Each subunit has 1 prosthetic haem group
– Iron II ions in the haem group can combine reversibly with an oxygen molecule enables it to transport oxygen around the body

– A fibrous protein
– Connective tissue found in skin, tendons, ligaments and the nervous system
– Many different forms but all are made up of 3 polypeptide chains wound together in a triple helix structure – long, strong rope like structure
– Every 3rd amino acid in the chain is glycine – a small amino acid. Small size allows it to form a closely packed helix
– Hydrogen bonds form between the polypeptide chains to form long quaternary proteins with staggered ends – allow proteins to join end to end forming long fibrils called tropocollagen