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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Hair Types – Follicles

When I was little, I would always look at my mom’s curly hair and wish my hair was like hers instead of being boringly straight. And this got me thinking, why did I have straight hair when she had curly hair? I mean, even my dad’s hair is a little wavy! So what is responsible for this difference between my hair and my parent’s hair; what causes different types of hair?

So many things apparently

I started looking into this a month ago, and I’m still reading about different factors that affect the type of hair you have: your follicles, the keratin in our hair, and genetics. But then, genetics is its own fountain of knowledge, where several of its drops contribute to our hair type. In other words, there are several different genes (and by several, I mean a lot) that affect whether we have straight, wavy, curly or frizzy hair. So I’m going to start with a simple factor for now, the follicle, and explore keratin and the genetics of hair at a different time.

The Role of Follicles in Hair Types

Shape

The shape of the follicles of our hair is a factor, as it dictates the shape our hair strands will take. The two shapes of follicles are circular and elliptical. There are several sizes of ellipticals, each of which gives rise to wavy, curly or frizzy hair, shown below.

Shape of follicle

This image is a little bit deceiving though; we know that there is more to the follicle than just the hole that hair grows from. Recall that there are two components to the follicle; the papilla and the bulb. The bulbs of your hair follicles are the components that actually determine the texture of hair you have. So while the tube itself is either circular or elliptical, it is more important for us to note what shape the bulb is. If the bulb is spherical, it will result in straight hair (even if the follicle tube looks like it’s elliptical)!

Hook

The presence of a hook is also a factor for the type of hair you have. By hook, I mean that the bulb sits at an angle. If you look at the images below, the follicle on the left is pretty straight as the bulb sits 90 degrees to the imaginary horizontal line (depicted in yellow)

(Bernard, 2003)

(Bernard, 2003)

The follicle on the right, however, shows that the bulb is sitting on an angle to the horizontal line. This causes some of the keratin molecules on one side of the follicle to be closer together than the other side, creating a curl.

And that’s all there is to know about the role of follicles in making hair curly or straight.

Next week: We’ll talk about what role keratin plays in determining hair type!

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Bernard B.A. 2003. Hair shape of curly hair. Journal of the American Academy of Dermatology: 48S120–S126. September 19, 2013.

Hair Colour

Last week, we talked about some of the roles of melanin in the body. This week, we’re going to focus on two types of melanineumelanin and pheomelanin and their role in causing hair colour.

What makes Eumelanin and Pheomelanin different?

It’s really their colour. Eumelanin is more dark brown/blackish while pheomelanin ranges from reddish colours to yellowish.

How is hair coloured?

Melanocytes provide the pigments that give hair its colour. These melanocytes are found in the follicle of the hair (remember, the follicle consists of the bulb of cells that receive nutrients from the papilla) and they are only active during the hair‘s growth phase. This phase is also known as the anagen phase of the hair‘s cycle.

There are different types of specialized melanocytes, which produce different types of melanin. Each specialized melanocyte differs in its shape. The melanocytes that produce eumelanin are oval-shaped while the melanocytes that produce pheomelanin are spherical.

The melanin molecules are formed and then uptaken by the bulb cells, which actively form hair. The shaft of the hair then shows the hair colour produced by the mix of eumelanin and pheomelanin molecules.

Different hair colours

Darker hair contains more eumelanin than pheomelanin while red hair and light hair have more pheomelanin than eumelanin. Naturally occurring hair colours are:

  • Black (Lots and lots of eumelanin, very little pheomelanin)
  • Brown (Higher amount of eumelanin than pheomelanin)
  • Blond –> From platinum blond to strawberry blond (Higher amount of pheomelanin, varying from the yellow pigments to the red)
  • Auburn –> this is a light to dark reddish brown colour (higher proportion of red pheomelanin than what’s found in brown hair)
  • Chestnut –> darker than Auburn.
  • Red (around 2/3 of the pigments are pheomelanin and 1/3 eumelanin)
  • Gray and White (Due to a lack in pigmentation and melanin)  When you age, you lose melanin in your hair and don’t produce as much melanin anymore, which is why your hair turns gray/white.

 

Breeling, J.L. 2008. Hair Colour: Biology, Mythology, and Chemistry. HairFoundation.org <http://hairfoundation.org/hair-library/article-hair-color.htm>. August 27, 2013.

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Melanin

Background Info

You might have guessed already that melanin is one of the pigments that causes the colour of your hair, skin and eyes. But did you know that there are several types of melanin?

That’s right, the pigment we thought we knew so well is actually a family of pigments. Melanin is produced by melanocytes and is formed by aggregating several different component molecules together. The variability in the combinations of molecules results in the different types of melanin. The exact composition and structures of these melanin molecules are still being researched. But it is known that the metabolism of an amino acid, tyrosine, is required to produce melanin.

Everyone seems to have a relatively similar concentration of melanocytes in their bodies; however, the frequency at which the melanocytes are induced to produce melanin varies with different ethnicities and individuals due to an increase or decrease in the expression of the melanin-producing genes.

Benefits to having a lot of melanin

This dark pigment allows for the absorption of UV radiation, which prevents our cells from dying or becoming cancerous. Melanin helps protect our DNA from being damaged by UV rays. This aspect is extremely important as DNA encodes almost all of the parts of our body, with the exception of the bacteria that exist inside and our mitochondria (which we inherit from our moms). If even a single mutation were introduced into our genome, there’s a chance that it will result in a malfunctioning protein which can lead to the breakdown of different biological processes.

For cold-blooded animals, melanin also provides a way to absorb heat from sunlight.

Disadvantages to producing a lot of melanin

Having too much melanin can mean that even the smallest of stimuli, like a scratch, can induce the production of more melanin. This results in the formation of dark patches of skin at those areas.

Two types of melanin molecules will be involved in next week’s post about Hair Colour, so stay tuned!

Simon, J.D. 2013. John D. Simon. Chem.virginia.edu. <http://chem.virginia.edu/faculty-research/faculty/john-d-simon/>. August 22, 2013.

Taylor, S.C. 2003. The Advantages and Disadvantages of Having More Melanin in Your Skin. About.com. <http://womenshealth.about.com/cs/dermatology/fr/brownskin_2.htm>. August 22, 2013.

Hair

What’s up with hair? I mean, we see a bunch of commercials telling us how to take care of it and how to impress other people with it, but what is it made up of exactly?

What is hair?

Hair is actually composed of four components: the follicle, the shaft, the inner and outer sheaths.

The follicle

The follicle is a tube-like structure located in our skin and it has two components: the papilla and the bulb. The papilla contains itty bitty blood vessels (called capillaries) which provide nutrients to a bundle of cells. This bundle of cells is referred to as the bulb. The cells in the bulb actually divide every 23-72 hours, which is faster than any other cell in our body!

The shaft

The shaft is the part of the hair that is visible to us. It is composed of three layers dead, hard protein called keratin. The innermost layer is called the medulla and isn’t always present. The middle layer is the cortex, which makes up the majority of the shaft,  and the outermost layer is the cuticle. The cuticle is formed by overlapping scales, somewhat like a roof.

The inner and outer sheaths

The follicle is surrounded by two sheaths, an inner and outer sheath, which help protect and mold the hair. The inner sheath ends just above the opening of the sebaceous gland (Remember those? They provide oil [sebum] to our skin and are found in the dermis layer of our skin!) and follows the rest of the shaft. The outer sheath encloses both the inner sheath and the follicle, and it ends just below the sebaceous gland.

And that’s the structure of hair! The follicle is similar to the roots of a plant in that it provides the nutrients and allows the hair to stay in the skin. Around the follicle are two sheaths, which wrap around it to add more stability and strength. Finally, the part we see everyday is known as the shaft of the hair. That’s all to it.

In the next few weeks, we’ll explore different topics involving hair like goosebumps,  curly hair, the colour of hair, and greying hair! There will be a few random topics sprinkled in there too before things get too hairy.

Yes, that just happened.

Brannon, H. 2006. The biology of hair. About.com. <http://dermatology.about.com/cs/hairanatomy/a/hairbiology.htm> August 7th, 2013.

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