My friend’s son bleached his hair last week, so I decided to study the science behind it. Before we start, we need to know the various names for different parts of hair:
When hair is bleached, melanin within the cortex is oxidized by hydrogen peroxide. The process of bleaching hair is known to be damaging, and I found a cool picture taken with scanning electron microscope that shows what happens to your hair follicles.
What the hair follicle looks like before and after bleaching:
Here is a cross-section of the hair follicle before and after bleaching:
A close up view of melanin after bleaching:
When hair is bleached, hydrogen peroxide first solubilizes melanin, then decomposes the melanin. Upon further bleaching, the molecular frames of the melanin granules are decomposed.
Effect of hydrogen peroxide on melanin solubilization:
There are two types of melanin in hair, and the balance between the two determines your hair color. Eumelanin imparts a dark brown or black color to hair, while pheomelanin gives hair a golden blond, ginger, or red color. The yellow tint that often remains when hair is bleached is due to keratin, a protein found in hair.
Hydrogen peroxide alone will not bleach hair. In order for hydrogen peroxide to access melanin in the cortex, it must get past the outer coat, or cuticle. Using ammonia, the pH is increased, causing the hair follicle to swell. This swelling “breaks open” the cuticle, allowing hydrogen peroxide to penetrate the cortex.
Effect of pH on hair swelling:
While the cuticle must be opened for bleaching to occur, this is damaging to the hair follicle. This is why conditioners are used after bleaching hair, which help close up the cuticle.
It seems that hydrogen peroxide also breaks down keratin, which is found in the cortex. Keratin contains disulfide bonds, which are broken by hydrogen peroxide. The breaking of these bonds are (I think) what causes the bad odor when you bleach your hair, as sulfur is released.
I have never bleached my hair, and am kind of glad now that I have not. Of course, I have dyed my hair darker, which is also bad for it. I went through a phase a few years ago where I REALLY wanted purple hair. When I realized that I would have to first bleach it, I decided I didn’t want it THAT much. 🙂
P.S. I just judged at the NE Regional Science and Engineering Fair and had a great time! I was especially excited to meet a girl named Emma whose project was about the effects of dye on hair. Great job Emma!
Immunohistochemistry (IHC) is a technique that is commonly performed in labs, and is used to identify cells or components of cells for viewing under a microscope. Here are a few sweet examples of IHC:
This picture shows villi from the small intestine, with nuclei stained red. Epithelial membranes are blue, and green labels the rapidly proliferating epithelial layer of the villi and the crypts. I found this picture on a great website called the Cell Image Library. Check it out sometime if you want to be amazed 🙂
This was taken by Jason Snyder, who has a great blog about neurogenesis which you can find here. Granule cell nuclei are labeled red, while astrocytes and radial glia are in white. Beautiful.
Last, here is a picture taken by myself of the dentate gyrus. Green labels nuclei, while red labels dividing cells (actually, dividing cells look yellow because they are both red and green). As you can see, cell division is kinda rare in the brain.
The post today is not focused on how IHC works in general, but rather the biochemistry behind it. So there will be no discussion about the difference between monoclonal and polyclonal antibodies, or what a negative control is, or the difference between primary and secondary antibodies, etc. This post will (attempt) to describe what ACTUALLY happens when an antibody binds a ligand, how EXACTLY a fluorophore works, and what fixation REALLY links.
So first, antibodies and their antigens, the celebrity couple of science. Sometimes they are together, sometimes they break up, but we always will think of them as a pair. Scientists may not know who Katy Perry is currently with, but they DEFINITELY know which antibodies go well with certain antigens, and get very upset when things don’t work out.
An antigen is a characteristic that is unique to the target you are looking for. For example, if we want to label neurons, we would find a component of the neuron that the surrounding cells don’t have.
The antibody is the labeling protein. In other words, it tags the cell you are looking for. Antibodies are very specific and will only tag the cells containing the unique antigen.
The use of antibodies in immunohistochemistry has a very interesting history. Did you know that the reason these antibodies work so well is the same reason why you won’t get chickenpox twice in your lifetime? When you get chickenpox, your body’s immune system creates antibodies that are specifically targeted to the chicken pox virus; that is, the virus antigen. After the virus leaves, your body still has those antibodies which are ready to fight the next time chickenpox tries to attack.
Antibodies for immunohistochemistry are made very similarly. The protein that you want to detect is first injected into a rabbit. Since this is not natural (just like chickenpox), the rabbit has an immune response and creates antibodies specifically targeted to the protein. Those antibodies are then collected from the rabbit and purified. Scientists then apply those antibodies to the tissue they are studying. I find it amazing that scientists have turned an already amazing phenomenon which saves people’s lives into a research tool which can then save more lives.
The main types of interactions that hold antigens and antibodies together are van der Waal forces, electrostatic interactions, and hydrogen bonds. No covalent bonds are formed when antibodies bind antigens. Van der Waal forces grow stronger when the distance between the antibody and antigen is reduced. When the structure of the antibody fits well with the antigen, the distance between them is shortened, allowing van der Waal forces to play a part. The same is true for electrostatic bonds. In electrostatic bonds, opposite charges attract. The amino acids arginine, histidine, lysine, aspartic acid and glutamic acid are electrically charged, so any protein with these amino acids can form electrostatic interactions with another charged protein.
One last bit of trivia: Temperature is an important factor in the association of antibody and antigen. This can be seen in an equation for the acid dissociation constant, KA =e–ΔaG/RT !
So that is just a little about the biochemistry behind IHC. Below are the sources that I used to create this post. If I have made any mistakes, I apologize, as I am learning this as I go along 🙂
In this post I hope to review the basics of enzymes and their application to laundry detergents, products that we (hopefully) use often. One of the first things I did in preparation for this blog was look at the ingredients in my own laundry detergent, all® small & mighty with stainlifters.
I looked at the list of ingredients on the back and….. I was very disappointed. “Cleaning agents (anionic and non ionic surfactants), buffering agent, stabilizer and brightening agent.”
Anyway, there are some laundry detergents that use enzymes, including Tide, Arm and Hammer, and Ultra Plus, which you can read about here. So what kind of enzymes are used in laundry detergents? They typically include proteases, lipases, and amylases . Some detergents also include cellulases and peroxidases, which remove soil and brighten colors, respectively. The list below was modifed from this paper if you want to read more.
Protease: Breaks down protein. Common protein stains include blood, sweat, egg, and grass.
Lipase: Breaks down lipid, AKA fat. Common stains are from butter, oil, and salad dressing.
Amylase: Breaks down starch-based residues found in food such as spaghetti, custard, chocolate, gravy, and potatoes.
Cellulase: Removes soil indirectly by breaking down cellulose. Used on cotton fabric, as it does not break down the cotton fibers.
Peroxidase: Bleaches dye that is released from fabric to prevent bleeding onto other fabric.
Before we discuss how proteases, lipases, amylases, etc. do their thing, let’s talk about enzymes in general. For all the reactions described above, energy is required. The more energy required, the slower the rate in which it proceeds. What enzymes do is reduce the energy required for the reaction to occur. For example, a protease reduces the energy input needed to break down a protein. Once the enzyme is added, the energy needed is lower, allowing the rate of the reaction to proceed. It’s kind of like having a sherpa with you when you climb Mount Everest.
Another important fact about enzymes is that once a reaction is done, the enzyme is still available to catalyze another one. In other words, a protease molecule can break down more than one protein. This is one of the main reasons why only a small amount of enzyme is needed to make a big effect in laundry detergent, something that producers definitely like.
Other reasons why laundry detergent companies like enzymes are
they are cheap
they have specific actions
they send less organic pollutants into the water
they are non-corrosive
Enzymes are relatively cheap because they can be made easily in large quantities, as long as you know a little about genetics and cell culture. Enzymes are “made” by growing cells that are known to produce a lot of the enzyme of interest. The types of cells often used are yeast, bacteria, or fungi. Once the cells have grown, they can be broke open and the enzyme you want can be isolated. Scientists have improved upon this method by altering the cells’ genome, causing the cells to grow abnormally high amounts of the enzyme desired.
A suitable enzyme for use in laundry detergents must also have the following characteristics:
compatibility with detergents (the actual detergent in “laundry detergent” can denature proteins, as we talked about last week in The Incredible Edible Egg. Since enzymes are proteins, they must be resistant to the detergents used to clean fabric)
must work at a variety of temperatures
must be stable at a pH range from 8 to 10.5
The ability of enzymes to work at a variety of temperatures, especially low temperatures, makes laundry detergent more environmentally-friendly. It also can replace old ingredients used in laundry detergents that are harmful to the environment.
Let’s select protease and lipase to see how they work.
Since we talked about eggs last week, lets pretend you got egg white on your shirt. The main protein in egg whites is albumin. So how does a protease break down albumin? Most commercially used enzymes are alkaline serine proteases (see this paper for a review about alkaline proteases). Serine proteases use 3 amino acids that work as the Three Musketeers also known as the catalytic triad to break bonds in albumin.
The protease and albumin bind, forming a Michaelis complex. The portion of albumin binding to the protease is shown in red.
Serine (Ser 195) from the enzyme attacks a bond in the protein albumin which connects its subcomponents, or amino acids, together. This attack causes the formation of a tetrahedral intermediate.
The tetrahydral intermediate changes into an acyl-enzyme intermediate due to general acid catalysis from histidine (His 57). The albumin bond has been broken, but albumin is still bound to the protease.
One part of the broken albumin protein is released.
The acyl-enzyme intermediate is deacetylated, forming a second tetrahedral intermediate.
The other half of the broken albumin protein is released. The protease is left in its original form.
Once you finally got that egg stain off your shirt, you had to be a klutz and smear some butter on it. What would you use to remove butter? Butter has a high amount of lipids called triacylglycerol, so a lipase would be a good enzyme to use.