Chemical Bonds in Spider Silk and Venom

Welcome back everyone! I bet all of you have been missing some quality information on spider silk and spider venom! So, let’s not delay any further and jump right in. What did we learn about last blog post? Was it: a. IMF, b. Covalent bonds and polar molecules, or c. the compounds contained in spider venom? Hopefully you all said all of the above, but if not, here’s a link to our previous blog post as a refresher. To build on top of that information we got in the last blog post, as well as the first, let’s start with venom first, and then go onto more complex explanations of spider silk. 

Polypeptides are one of the major components of spider toxins, as you may recall from our previous blog post.  Ion channels, or groups of proteins, are situated on the nerve cell membrane and can move across the membrane. These channels control the electrical potential of the membrane and therefore plays a vital role in neurotransmitter release. The three main types of ion channels are Calcium, Sodium, and Potassium channels. Still following? Good. Now let’s move onto the next component of spider venom.

Additionally mentioned in our last blog post, the next important part of spider venom is its containment of polyamines. Spiders use their venom for immobilizing their prey and defending against attacks from predators. In both situations, spiders produce venoms that contain a substance called acylpolyamines. As shown by the chemical structure of an acylpolyamine molecule shown below, the structure is composed of a string of NH (amino) groups attached with an amino acid to an aromatic ring. The existence of an aromatic ring in the chemical structure has no effect on the poisonous qualities of spider venom, but more information on aromatic rings can be found here. The most significant aspects of the structure of the acylpolyamine molecule are the NH (amino) groups that allow the molecule to bind to the neurons that directly block neurotransmitters in the nervous system. This blockage of neurotransmitters causes the whole nervous system to shut down, thereby immobilizing the victim.

Now let’s move onto spider silk, a protein fiber produced by spiders! The first thing that may come to mind when you hear the words “spider silk” is that the webs you can find in bushes outside in the morning or in a dusty corner of the house. However, other than its aesthetics, spider webs serve more pragmatic purposes for spiders, such as the construction of traps to ensnare other insects or the creation of cocoons to provide protection for their eggs. Although spiders optimize their silk production for the function that the silk is most needed for, we can assume that these different types of silk all have similar chemical properties that attribute for their astounding physical properties.

A spider web demonstrating how its physical property of hydrophobicity.

These spider silks, in comparison to high-grade steel, have comparable tensile strengths and a sixth of the density, while still managing to be able to stretch up to five times its original length. These fibers can not only absorb a lot of energy while keeping its ductility, but it can also maintain these properties from a range of -40°C and 220°C. On top of all of this, spider silk is insoluble (does not form a homogenous solution when put in water) and antimicrobial!

So, what makes this silk so special? While some of its properties are explained through complex biological concepts such as protein hierarchy and crystallineamorphous interactions, many of them can also be largely attributed to concepts brought up in our last blog post: the polarity of certain molecules and intermolecular forces. In the spider silk protein’s primary structure, otherwise known as the sequence of amino acids that make up the protein, you can find mainly two nonpolar amino acids: glycine and alanine. The forces between the blocks of alanine and the blocks of glycine contribute to its strength, since these two smallest amino acids can interact to form tight packs. Furthermore, certain areas made up of alanine, known as the crystalline regions, are very hydrophobic. This means that water cannot penetrate these hydrogen bonded sheets, lending silk its insolubility. However, spider silk also contains polar amino acids, such as arginine. These polar molecules contribute to its initial solubility during production, as well as to polar interactions and bonding later on.

Besides its amino acids, another component of this silk that contributes to its amazing properties is potassium hydrogen phosphate. Because potassium hydrogen phosphate is a proton donor in aqueous solution, the silk becomes acidic. This increased acidity gives the silk some of its antimicrobial effects, preventing bacteria from denaturing the fibers and protecting the possible contents within the silk.

I think its time to wrap this blog post up. So, just to recap on everything we talked about, here’s a short summary of what our third blog post covered. First we discussed the Calcium, Sodium, and Potassium ion channels that allow spider venom to have drastic effects on the nervous system. We also dissected the structure of spider venom and pinpointed the specific compound that allows spider venom to easily bind to neurotransmitters. Do you remember what these were? They were the NH(amino) groups! Next, we talked about the various chemical properties of spider silk that give it its high tensile strength, such as its antimicrobial properties which come from the potassium hydrogen phosphates in its composition. So this sums up our blog post, thanks for reading!

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