How Does a Perm Curl Your Hair?
or
Breaking and Remaking Bonds!
Name: ______
Since ancient times, people have experimented with many ways to change their hair. The Assyrians favored curly hair, the Egyptians wore wigs, and the Romans used curling irons. Today, it seems that people with straight hair want curls and the curly-haired people covet straight hair. Now, we can change the shape of our hair with permanent waving or hair straightening products. How do these products work and what do they do to the hair?
The part of hair we see is called the hair shaft. The outer layer, the cuticle, consists of dead cells that overlap each other like the shingles of a roof. Inside the cuticle is the cortex, which contains the protein keratin. Proteins are large molecules made of smaller amino acid molecules. Hair keratin contains the amino acid cysteine which has a sulfur atom projecting out of the protein backbone. As the hair shaft emerges from the follicle, the keratin hardens because sulfur-sulfur (“disulfide”) bonds form between different keratin proteins. The disulfide bonds cross-link (or connect) one protein backbone to another, this is extremely durable and gives the hair its strength.
Three of these combined proteins form into an interwoven coil called a protofibril; then eleven protofibrils bond and coil together to make a microfibril; finally hundreds of microfibrils are cemented into an irregular bundle called a macrofibril. These in turn are mixed with dead and living cells to make a single strand of hair.
Most of the permanent treatment for hair must affect the inner layer of the hair, the cortex. Chemicals are used to penetrate the outside protective layer, the cuticle, and alter the arrangement of the sulfur bonds. Moist hair is wrapped around a roller (B) and the hair becomes stressed because the outer protein stretches more than the protein next to the roller. When the waving chemical is applied, the disulfide bonds are broken, and the protein molecules slide past each other, relieving the stress (C). After the waving solution is rinsed from the hair with water, the neutralizing solution is applied. This causes disulfide bonds to re-form, but in new locations (D). In a typical waving, 20% to 30% of the disulfide bonds are broken.
Pre-Lab Questions
1. What is the part of hair you see called? What is this part of hair made up of?
2. What types of molecules make up the cortex of hair? What smaller molecules go together to make these up?
3. Explain, using 2 sentences, what makes hair strong?
4. Explain, in your own words, using 3 sentences, how a permanent wave treatment works to curl hair. (Include the specific bond that is being manipulated in this process.)
Step / Procedures / Comments, Observations, Errors and Data1 / · Wrap 5 (five) strands of hair around 5 (five) different glass stir rods and secure each with a rubber band / Na
2 / · Submerge 3 hair samples into NaOH solution
· Submerge 2 hair samples into water / Na
3 / · Take another (6th) strand of hair and make a wet-mount slide by placing the hair and 1 (one) drop of water on the slide
· Observe using the microscope / Sketch hair here:
4 / After 15 minutes
· Remove 1 of the hair samples from the NaOH and rinse with water
· Remove 1 of the hair samples from the water
· Carefully remove the hairs from the stir rods and examine on a slide under the microscope / Sketch each hair here:
Step / Procedures / Comments, Observations, Errors and Data
5 / After 30 minutes
· Remove the second hair sample from the NaOH and rinse with water
· Remove the remaining hair sample from the water
· Carefully remove the hairs from the stir rods and examine on a slide under the microscope / Sketch each hair here:
6 / After 30 minutes
· Remove the remaining hair sample from the NaOH and rinse with vinegar
· Dry the hair for 5 minutes
· Carefully remove the hairs from the stir rods and examine on a slide under the microscope / Sketch hair here:
Analysis
1. What served as the control in this experiment?
2. Compare and contrast the permed hair at 15 and 30 minutes. What happened over time?
3. Compare and contrast the permed hair to the control. How were they different? Does the perm really work?
4. What does the NaOH do to the hair?
5. What purpose does the curler (glass stir rod) serve in this process?
6. What purpose does the vinegar serve? Why did you rinse the permed hair with vinegar?
7. Did your samples become permanently curled? Why or why not?