Parrot pigmentation by functional group

Directions for teachers:
After reviewing the basics of molecular structure and bonding, use this activity to introduce functional groups and their importance. For the first section, draw or project the molecular structures of aldehyde psittacofulvin and carboxyl psittacofulvin on the board. (You’ll likely want to draw the expanded structural formulas, annotating all carbon and hydrogen atoms with C and H, instead of showing students the skeletal structures.) Students should work in pairs to create a Venn diagram comparing the two molecules. Then ask students to use an online, free molecule builder to take turns building each molecule to visualize their three-dimensional structures. Students will then work together to define aldehyde and carboxyl functional groups and discuss why functional groups on molecules are important.  

Students should then read the article “A single enzyme can alter the vibrant colors in parrot plumage” and use information given in the article to describe the colors seen in a parrot picture by pigment and structure. Finally, use the third section of this lesson plan to have students individually explore other examples of functional groups and the importance of their properties and reactivity.    

To learn more about the chemistry of pigments and how they interact with visible light, explore this Colorful Chemistry lesson plan.

Functional groups
Follow instructions from your teacher to complete this first section with your partner.  

1. Compare the molecules aldehyde psittacofulvin and carboxyl psittacofulvin using a Venn diagram.   

Aldehyde psittacofulvin and carboxyl psittacofulvin both have a chain of 16 carbons covalently bonded. They each have 8 double bonds, and the rest are single bonds. One double bond is from carbon to oxygen and the rest are carbon to carbon. Aldehyde psittacofulvin has a terminal hydrogen and carboxyl psittacofulvin has oxygen bonded to a hydrogen atom at the end of the molecule.  

2. Use a free molecule builder, such as https://molview.org/, to build the two molecules and view the three-dimensional structures. How is the two-dimensional structure different than the three-dimensional structure? 

In the three-dimensional structure, you can see the correct orientation for all the atoms, including the hydrogen atoms. The two-dimensional structure doesn’t show that two of the three hydrogens at one end of these molecules are in a different plane than the rest of the atoms. 

3. Organic, or carbon-containing, molecules are often categorized by the functional groups that they contain. Based on the structures of aldehyde psittacofulvin and carboxyl psittacofulvin, how would you describe an aldehyde functional group? What about a carboxyl functional group?  

An aldehyde functional group has a carbon double bonded to oxygen. The carbon is also bonded to one hydrogen atom and to the long carbon chain. A carboxyl functional group has a carbon double bonded to an oxygen atom. The carbon is also bonded to another oxygen that is bonded to a hydrogen atom, and to the long carbon chain. 

4. Look up general properties of these functional groups. Why do you think scientists would categorize some organic molecules by functional group? 

Carboxyl groups can release hydrogen ions and are therefore acidic. Aldehydes are easily oxidized and converted into carboxylic acids. Functional groups determine many chemical and physical properties of organic molecules, so categorizing molecules by functional group can help predict interactions and reactivity of the molecules.   

Paint a parrot by pigment and structure
Read the article “A single enzyme can alter the vibrant colors in parrot plumage.” Take notes and use information to complete the following prompt: 

Find a picture of a parrot and describe its coloration. Explain what scientists might find about the molecular makeup within or on feathers to create each section of color on the parrot. When necessary, indicate the relative amount of the different types of pigments.  

Student answers will vary. Having aldehyde psittacofulvin alone in feathers makes them red, and having carboxyl psittacofulvin alone in feathers makes them yellow. Blue tones come from nanostructures on the feathers. Melanin controls black, gray and brown colors in parrot feathers. Orange feathers are created from equal amounts of both types of psittacofulvin. Greens are created when carboxyl psittacofulvin is present in feathers that are topped with blue nanostructures. Purple may be created by blue nanostructures on top of aldehyde psittacofulvin.  

Functions of functional groups
According to instructions from your teacher, complete the following questions.  

1. Read this short Scientists Say: Amino Acids article. What are the functional groups in an amino acid? What basic function do amino acids serve in animals? How do the 20 different amino acids differ from each other? 

Each amino acid has an amine, a nitrogen atom bonded to two hydrogen atoms, and a carboxyl group, a carbon atom double bonded to an oxygen atom and single bonded to a different oxygen atom that is also bonded to a hydrogen atom. The carbon in the carboxyl group and the nitrogen in the amine group are both bonded to another carbon atom, which is also bonded to an R group (a carbon atom, carbon chain of atoms, or hydrogen). Amino acids are the building blocks of all proteins that are needed for survival in animals, including humans. Each type of amino acid has a different R group.   

2. As you’ve seen, functional groups determine many chemical and physical properties of organic molecules. Understanding functional groups’ structure, reactivity and properties is important in many fields. Choose a field that interests you, such as medicine, drug development, immunology, genetics, toxicology, food and product development, material science, etc., and find another example that illustrates the importance of understanding functional groups in a molecular structure.    

Answers will vary.