Editing Keratin (section)

==Silk==
{{More citations needed|date=January 2022}}
The [[silk]] [[fibroin]]s produced by [[insect]]s and [[spider]]s are often classified as keratins, though it is unclear whether they are phylogenetically related to vertebrate keratins.

Silk found in insect [[pupa]]e, and in [[spider web]]s and egg casings, also has twisted β-pleated sheets incorporated into fibers wound into larger supermolecular aggregates. The structure of the [[spinneret (spider)|spinneret]]s on spiders' tails, and the contributions of their interior [[gland]]s, provide remarkable control of fast [[extrusion]]. Spider silk is typically about 1 to 2 micrometers (μm) thick, compared with about 60&nbsp;μm for human hair, and more for some mammals. The [[biology|biologically]] and [[commerce|commercially]] useful properties of [[spider silk#Properties|silk fibers]] depend on the organization of multiple adjacent protein chains into hard, [[crystal]]line regions of varying size, alternating with flexible, [[amorphous]] regions where the chains are [[random coil|randomly coiled]].<ref>{{cite web | vauthors = Australia | title = Spiders – Silk structure | url = http://www.amonline.net.au/spiders/toolkit/silk/structure.htm | publisher = Amonline.net.au | access-date = 2010-09-23 | url-status = dead | archive-url = https://web.archive.org/web/20090508161836/http://www.amonline.net.au/spiders/toolkit/silk/structure.htm | archive-date = 2009-05-08 }}</ref> A somewhat analogous situation occurs with [[chemical synthesis|synthetic]] [[polymer]]s such as [[nylon]], developed as a silk substitute. Silk from the [[hornet]] [[Silkworm cocoons|cocoon]] contains doublets about 10&nbsp;μm across, with cores and coating, and may be arranged in up to 10 layers, also in plaques of variable shape. Adult hornets also use silk as a [[adhesive|glue]], as do spiders.