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What Happened to Beau?

How Amino Acids Affect Keratin Organization in Hair


Dan Johnson
Biology Department
Wake Forest University


This flipped case was designed to introduce students in a general introductory biology course to basic protein structure. The two videos and interrupted case use keratins in hair as model proteins. From the videos students learn how amino acids regulate protein structure, and how small changes in amino acid sequence have large impacts on overall protein organization and function. The case story focuses on a puppy whose hair changes from straight to curly when it sheds its coat. The protagonist tests the adult versus puppy hair, and discovers that the amino acid composition is different in the curly versus straight hair samples. Students apply basic principles of protein structure to hypothesize why the dog's coat switched from straight to curly. The case intentionally stops short of providing a complete answer to the mystery, so students think through the molecular processes logically rather than having a final "correct" answer. An optional activity is provided that makes the case more appropriate for an introductory cell biology class.

  • Learn basic properties of proteins, e.g., that the shape of a protein is determined by molecular interaction forces, which are in turn defined by amino acid sequences.
  • Practice identifying patterns in tabulated data.
  • Correlate physical and biochemical evidence with descriptive observations.
  • Make provisional hypotheses, then revise or eliminate them based on subsequent evidence.
Keywords: protein; protein structure; amino acid; keratin; peptide; hair; curly; folding;
Topical Area: N/A
Educational Level: Undergraduate lower division
Formats: PDF
Type/Method: Discussion, Flipped, Interrupted
Language: English
Subject Headings: Biology (General)   Cell Biology  
Date Posted: 7/15/2017
Date Modified: N/A
Copyright: Copyright held by the National Center for Case Study Teaching in Science, University at Buffalo, State University of New York. Please see our usage guidelines, which outline our policy concerning permissible reproduction of this work.

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Supplemental Materials

The optional supplemental material below is recommended for use with this case study.

  A Decade After the Genome, Scientists Map the "Proteome" “Science
Audio file created by: Science Friday. Produced by: Christopher Intagliata. Running Time: 11:53 min. Date: May 30, 2014. Nearly all the body's cells contain identical DNA. So why does a neuron grow up so differently than a liver cell? Proteins are the key, says Akhilesh Pandey, a professor at the Johns Hopkins University. Two recent papers in Nature (one by Pandey's team) catalog where in the body certain proteins are found. But what matters isn't just where proteins show up, it's how they twist and fold, says David Pincus, a fellow at MIT's Whitehead Institute. Protein misfolding, for example, is a hallmark of neurodegenerative disease.
  Mapping Genes to Traits in Dogs Using SNPs hhmi/
In this hands-on genetic mapping activity, students identify single nucleotide polymorphisms (SNPs) correlated with different traits in dogs. Produced by HHMI BioInteractive.


The following video(s) are recommended for use in association with this case study.

  Protein Structure, Part 1: Where Are Proteins? What Do They Do?
This video leads students through an overview of general protein structure, with emphasis on keratin. Students learn that proteins are composed of 20 different amino acids and that the sequence of amino acids gives each protein its unique properties. Running time: 5:35 min. Created by A. Daniel Johnson for the National Center for Case Study Teaching in Science, 2016.

  Protein Structure, Part 2: How and Why Do Proteins Fold Into Complex Shapes?
This video explores the role of amino acid sequence in protein structure, how hydrogen bonding of the peptide backbone creates the secondary structure of proteins, and how intra- and intermolecular interactions define tertiary and quaternary structure respectively. Students also learn how keratins are assembled in hair. Running time: 12:28 min. Created by A. Daniel Johnson for the National Center for Case Study Teaching in Science, 2016.

  Dog Breeding hhmi/
This short video discusses how the many forms of dogs that exist today were all created through selective breeding from the dog's ancestor, the wolf. In a span of less than 10,000 years, breeders have changed traits and body shapes of dogs by artificial selection. For example, emphasizing different aspects of hunting and herding behavior. Produced by HHMI BioInteractive. Running time: 1:53 min.

  Dog Genomics and Dogs as Model Organisms hhmi/
In this video lecture, Dr. Elinor Karlsson of the Broad Institute discusses using dogs in genome-wide association studies (GWAS), and the genetic evidence for dog domestication, as revealed by copy-number variations in the amylase gene. Produced by HHMI BioInteractive. Running time: 29 min.

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