Keratin and its Bonds

Hi, hello! Last week, I promised to talk about Keratin’s role in hair types. This will, unfortunately, have to wait until next week because, before we can talk about keratin’s affect on hair type, we need to talk a little about keratin and a lot about its bonds!

Keratin is a protein

Keratin molecules, perhaps you recall, are fibrous proteins. Like all other proteins, it is made up of different subunits (called amino acids). Each of these subunits have atoms like carbon, nitrogen, oxygen, hydrogen and, sometimes, sulfur. Long chains of these keratin molecules make up the shafts of our hair (and also our nails! Cool, right?).

Keratin likes bonding

When I say ‘bonding’, I don’t mean like, “Hey man, let’s be friends”-type bonding. When I say bonding, I’m actually referring to chemical bonds… but, actually, let’s run with the analogy. Let’s pretend that keratin molecules are like children in kindergarten and everyone in class is required to hold each others hand (and not let go) in order to form two separate lines. That means everyone, except for the two children at both ends of each line, are holding two hands. Now, the two lines are brought closer together, so that some of the children in one line can interact with others in the other line. Here are three interactions we want to focus on:

  1. Some children have one ribbon tied to their right feet, which can be tied to other children with ribbons. The only way to separate them after this is to cut the ribbon.
  2. Some of the children in the 2 lines have a few magnets on their hips. When 2 children have the opposite poles facing each other, they are brought closer together to let their magnets connect.
  3. Finally, a few of the remaining children are blowing bubble whistles, which some of the other children spend time popping.

These three interactions have some of the same qualities of the bonds that the keratin molecules in our hair are capable of, which are shown below:

The three types of bonds that keratin molecules are able to form.

  1. The ribbons here represent something called a disulfide bond. This is simply a chemical bond between two Sulfur atoms (remember, sulfur is found on some of the subunits in a protein). Like the children, it’s hard to separate molecules (in this case, keratin molecules) with this bond unless the equivalent of scissors cuts the bond. For disulfide bonds, its equivalent to scissors is heat. Heat disrupts the bonds between the sulfur atoms, which allows them to be separated and form new bonds with other sulfur atoms if they want. Just like the children’s ribbons, one sulfur atom can only bind with one other sulfur atom.
  2. In keratin molecules, the magnets are actually opposite charges. Much like magnets, where the North and South ends are attracted to each other, the attraction is there for molecules that have positive and negative charges. The bonds that result from the interaction of these charges are called salt bonds, or sometimes salt bridges. These bonds aren’t particularly strong; like children with magnets, it’s fairly easy to separate them. At the same time, it does offer some stability to the actual chain of proteins.
  3. The children blowing and popping bubbles represent molecules that are partaking in hydrogen bonding. This bonding actually involves no contact between the atoms; it is instead a general attraction between atoms with a slightly positive and slightly negative charge. Most commonly, hydrogen bonding occurs between oxygen and hydrogen molecules or nitrogen and hydrogen molecules. These bonds are really weak and temporary. In the analogy of the bubbles, the bubbles approaching the children represent the attractive force of hydrogen bonding; the child is happy that the other child blowing the bubble blew it her or his way. But once the bubble is popped, the child has no reason to be thankful to the bubble blower and the attraction is lost; the bubble blower will blow bubbles towards another unoccupied child while his or her first bubble popper will turn to a different bubble blower. Similarly, the atoms with slightly positive charges will be attracted to any atoms with slightly negative charges… but it will just be a fleeting crush, nothing dependable.

Finally, the hand-holding represents the bonds between the keratin molecules to make  the chain. These bonds are extremely strong, but can be broken (like when you cut your hair, or even burn it).

And those are the bonds that keratin molecules form! It’s a lot to take in, I know. But next week, we’ll go into the role that these bonds have in hair types!

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