Thursday, March 1, 2018

Today, I looked at the primary and secondary structure of spider silk.

Side note, apparently spider silk has low birefrigence. Now this actually is okay, because you don't want the index of refraction to change much if used in fiber optics. And, because it's already been used/planned to be used in molecule detection, it's been proven to be applicable there.

Okay, now, structure. Primary structure is fairly simple and I discussed it some in my presentation. Primary structure of spider silk is mainly (90%) repetitive amino acid sequences. Most of these amino acids are glycine and alanine. This chart I made shows the molar %. --->

Image result for beta sheet
"Structural analysis revealed that oligopeptides with the sequence (GA)n/(A)n tend to form α-helices in solution and β-sheet structures in assembled fibers." This allows for the elasticity of spider silk. ( A β-sheet looks like a piece of paper that's been creased along the length so it looks like... nevermind, here's a picture: --->) So when stress is applied, the protein will stretch ("straighten out"...?) instead of breaking. The repetitive protein sequences is also crucial to its tensile strength. 

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Object name is prion0204_0154_fig003.jpgHowever, at the terminals (ends) of the protein, there are nonrepetitive proteins. These are crucial for protein assembly because they form intermolecular bonds that stabilize dimers (2+ monomers), etc. during the "assembly." 

At a more macroscopic level, spider silk looks more like a rope that's coated in a protective "skin."  In this diagram, you can see the macroscopic view with a diameter of 1-50𝜇m (1𝜇m = 1x10⁻⁶m). Then there are subunits (diameter of 2nm and average length of 7nm. 1nm = 1x10⁻⁹ m) which are comprised of the repetitive amino acid sequences which form the β-sheet structures (in blue). 

We still don't fully understand the entire structure and functions within the spider silk. It's probably one of the most complicated structures we know of. But it's also fascinating, so I will do all that I can to learn as much as I can about the structure, at least enough to present my thesis, which I think I've surpassed already. (At least I'll have plenty to write about.)

So what I know right now isn't even scratching the surface of the current understanding, and there's no way I will know as much as we know, that would take years. Really, as long as I have a fundamental understanding of how the structure works, how it changes during fiber formation, and how the structure gives silk its properties, I'll be set. Next week, I'll focus on tertiary and quarternary structure, and begin looking at making a step by step journey through silk synthesis in nature, so that I can compare it to laboratory methods later. 

- Noah

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