1 A model of a protein molecule — myoglobin, a protein present in 

 muscle and other tissues, which serves as an oxygen store. Poly- 

 peptide chains are white; the grey disc is the haem group. The small 

 spheres are marker atoms attached to the molecule. Marks on the 

 scale are 1 Angstrom Unit (10"* cm.) apart. (Photograph by Dr J. 

 C. Kendrew) 



