Conservation Science

86 Chapter 4

The bulk of the fibre consists of the cortex. The elongated cortical cells are
composed of crystalline proteins within a sulfur-rich amorphous protein matrix.
The keratin adopts two principal secondary structural motifs, the - and -
helices, which form due to extensive hydrogen bonding and steric factors, with
large side-groups arranged around the spiralling peptide backbone. In the crys-
talline regions of the fibre, superhelices or protofibrils are formed from the
-helices (Figure 25) which are themselves arranged in a helical fashion. These
are then organised to form microfibrils, which in turn form macrofibrils; these,

-Helix

Microfibril

Macrofibril

Superhelix

Paracortex

Cortical Cell

Cuticle Cell

Orthocortex

Figure 23The hierarchical microstructure of wool