structure

• • 4 levels of organisation
• • Primary structure – linear polypeptide chain of amino acids 
• •  Secondary – the folding or coiling of the polypeptide chain into either a helix (spiral) or pleated sheet due to hydrogen bonding
• • Tertiary structure – more bonding between the helices and pleated sheets causes the single polypeptide to fold into a more complex 3-D shape (this is the final structure for some proteins) 
• •  Quaternary structure – two or more polypeptides join to create a more complex 3-D structure for a single functional protein and may include a prosthetic group (organic or inorganic compound) 
• • Proteins containing a prosthetic group are called conjugate proteins