Youtor
Cysteine sulfur disulfide bonds amp reducing agents oxidation reduction nucleophilicity etc
>> YOUR LINK HERE: ___ http://youtube.com/watch?v=5gwHl8dXc9s
Cysteine crosslinks (disulfide bonds), cysteine oxidation, reducing agents in the body the lab. The Sistine Chapel wasn’t built in a day, but thanks to the amino acid cysteine (Cys, C) your hair can be curled in one! Although the history of cysteine research is a bit hairy - It was hard to even find it in proteins at all. You might have heard of the curse of Tutankhaman - well, biochemists spoke of a kind of curse of cysteine research - from disappearing samples to disappearing researchers, early cysteine investigations were beset with problems. But eventually they were able to figure it out - and now we know so much about it we can take advantage of its unique property to form special links to curl our hair or straighten out its kinks! • blog form: http://bit.ly/cysteinecrosslinks • It’s Day 11 of #20DaysOfAminoAcids - the bumbling biochemist’s version of an advent calendar. Amino acids are the building blocks of proteins. There are 20 (common) genetically-specified ones, each with a generic backbone with to allow for linking up through peptide bonds to form chains (polypeptides) that fold up into functional proteins, as well as unique side chains (aka “R groups” that stick off like charms from a charm bracelet). Each day I’m going to bring you the story of one of these “charms” - what we know about it and how we know about it, where it comes from, where it goes, and outstanding questions nobody knows. • More on amino acids in general here http://bit.ly/aminoacidstoproteins but the basic overview is: • amino acids have generic “amino” (NH₃⁺/NH₂) “carboxyl” (COOH/COO⁻) groups that let them link up together through peptide bonds (N links to C, H₂O lost, and the remaining “residual” parts are called residues). The reason for the “2 options” in parentheses is that these groups’ protonation state (how many protons (H⁺ ) they have) depends on the pH (which is a measure of how many free H⁺ are around to take). • Those generic parts are attached to a central “alpha carbon” (Ca), which is also attached to one of 20 unique side chains (“R groups”) which have different properties (big, small, hydrophilic (water-loving), hydrophobic (water-avoided), etc.) proteins have different combos of them, so the proteins have different properties. And we can get a better appreciation and understanding of proteins if we look at those letters. So, today let’s look at Cysteine (Cys, C) • Cys’ side chain is a -CH₂-SH group. -SH is called a THIOL (it’s alcohol’s (-OH) sulfur CYSter). More on alcohols here: http://bit.ly/2QWKWXp but it just refers to molecules having hydroxyl (-OH) group(s). So not all alcohols are “alcoholic” in the social outing sense. Anything with an -OH is an “alcohol” in the chemistry sense, so things like sugar are super alcoholic. • Cysteine isn’t gonna get you drunk, but the thiol can lead to some protein personality changes! 2 Cys (either within the same protein or between 2 proteins) can link together (protein)-SH + HS-(protein) 👉 (protein)-S-S-(protein) to give you a DISULFIDE BOND or “cross-link” between 2 Cys residues in the same or different proteins • SH + -SH ⇌ -S-S • More on what these terms mean in a sec, but the key take-away is that, unlike other charm-charm interactions, which are just attractions based on charge (or partial charge) differences, this is a “covalent bond”, so it’s strong (and good for sturdying-up secreted proteins that have to live outside the comfort of the cell). For example, pairs of disulfide bonds are used to keep the 2 separate peptide chains of the hormone insulin connected as it travels throughout your bloodstream to tell cells to let in and use glucose (blood sugar). • BUT these Cys-Cys bonds aren’t quite as strong as the covalent bonds in the protein’s backbone (linking the chain links) so you can split them back up without splitting up the chain links. This splitting unsplitting involves REDuction OXidation (REDOX) reactions, which involve thing 1 (the reductant) giving e⁻ to another thing 2 (the oxidizer), reducing thing 2 oxidizing thing 1 in the process. You can remember this with the mnemonic OIL RIG: Oxidation Is Loss (of e⁻), Reduction Is Gain (of e⁻) • But I haven’t really explained what electrons are, so let’s back up a sec and review. Atoms (like individual C’s, H’s, O’s, N’s) are really tiny, but they’re made up of even tinier parts called “subatomic particles,” which include electrons, protons, and neutrons. Electrons are negatively-charged subatomic particles that whizz around in “electron clouds” around a dense central core called the atomic nucleus where positively-charged protons (with some gluing together help from neutral neutrons) are tasked with reigning them in. • Finished in comments
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