Biochemistry 2280A Lecture : Quarternary Structure
Document Summary
Beta pleated sheet is made of one polypeptide chain not several wrapped around itself not several polypeptide chains. Many proteins are composed of multiple polypeptide chains or subunits. The cro- repressor for example is a homo dimer formed from 2 identical subunits. The subunits join in a head to head fashion as 2 small beta sheets, 1 form each subunit zipper up and form a larger beta sheet. Each pair of 2 subunits is held together in a head to tail fashion by repeated use of the same binding attraction. This becomes clear when the polypeptide chains are coloured in a random pattern so that the same region of each subunit have the same colours. Each subunit consents whether each neighbouring group has oxygen they communicate. Estrogen receptor b is a homo dimer because the 2 subunits are identical. P53 is a tumor suppressor gene and it is mutated in 50% of all cancers.