Amazing natural fibers: spider webs, Abaca fibers, and DNA

Natural fibers, like hair, silk, wool, and Abaca fibers have long strings of amino acids, with each molecule attached to the next - like a chain of paper clips.

The amino acid molecules connect through strong structural bonds. Those bonds need enzymes to break them. The long chains of amino acids form microscopic threads. 

Thicker strands form when those threads of amino acid chains connect to each other, like a stack of pliable railroad tracks. For example, each strand of human hair is made (among other things) of hundreds of those amino acid chains).

Connections between threads of amino acid chains include weak hydrogen bonds, like those dashed lines shown in the image on the right.

The easiest way to think of these living systems is through an analogy: thinking of sturdy molecular systems as furniture that is glued together.

Having hydrogen bonds is nature’s way of giving flexibility to structural elements.

It is certainly easier to separate two glued pieces of furniture at the glue joint by softening the glue with solvent than it is breaking down the wood and repairing that.

Most importantly, hydrogen bonds get created virtually instantly when necessary.

Let’s take spider web silk as an example: the spider produces a mass of protein strands in its silk gland; these proteins are swimming in a soupy fluid in the spider’s silk-producing gland.

The protein strands are attached to each other only at one end, close to the opening of the gland. That allows the strands to stay unattached and floating free within the gland's fluid, like strands of pasta in a large pot of hot water.

When the spider wants to use the silk (either to escape or make a spider web) it attaches the first portion of the joined protein strands to a stationary object, say a tree branch.The strands then pass through an increasingly narrow spigot at the entrance of the silk gland.

What is the result? the protein filaments are squeezed together in the micro-hair-width spigot tunnel and the excess water is removed.

This would be similar to grabbing a bunch of wet spaghetti pasta strands at one end with tweezers and then passing the lot through an ultra-thin funnel; the water would be squeezed out and the strands would stick together.

For the spider, passing the silk through the very narrow spigot encourages the virtually instantaneous formation of hydrogen bond links between the touching strands of molecules.

As the spider spools out the silk string, the protein strands zipper themselves together making one long silk thread.

Having the protein strands in a soluble state until they are ready to be used prevents congealed and tangled silk threads;

Snarled and knotted spider webs would bode poorly for survival for that species of spiders.

Speaking of cooking spaghetti, one way to test whether the pasta is cooked is to take one strand of spaghetti and throw it at the wall. If it sticks, the spaghetti is cooked! this is because enough of the starch has spread out/moisturized to allow hydrogen bonds to form between the molecules of the starch and those on the wall.