<unk> s, also called scleroproteins, are long filamentous<unk>  molecules that form one of the two main classes of tertiary structure<unk>  (the other being globular<unk> s).<unk> s are only found in animals.<unk> s form 'rod' or 'wire' -like shapes and are usually inert structural or storage<unk> s. They are generally water-insoluble and are found as an aggregate due to hydrophobic R-groups that stick out of the molecule.
The amino acid sequences they are made from often have limited residues with repeats. These can form unusual secondary structures, e.g. collagen triple helix.
The structures often contain 'cross-links' between chains, for example cys-cys disulphide bonds between keratin chains.
Globular<unk> s tend to denature more easily than<unk> s.<unk> s are usually used to construct connective tissues, tendons, bone matrix and muscle fiber.
Examples of<unk> s include keratins, collagens and elastins.
Fibrous protein
Fibrin
Immunoglobulin G
Immunoglobulin E
Beta globulins
Immunoglobulin A
Immunoglobulin M
Lipoprotein