Protein Train




Children learn about the "Protein Train". This purpose of this activity is to explain what happens to protein foods when they are eaten and how phenylalanine can become elevated in a person's blood.



After completing this activity, children will be able to:

  • state that the part of protein that a person with PKU has trouble with is phenylalanine
  • understand the basics of protein metabolism, including:
    • when protein is eaten, it goes to the stomach and is broken up into little pieces (amino acids)
    • the little pieces (amino acids) are taken into the blood
    • in the blood, the amino acids are carried throughout the body and used for growth, and to build muscle and other protein
  • explain that when phe gets into the blood of a person with PKU it doesn't get carried throughout the body and used like it should. It stays in the blood, resulting in high blood levels.



Explain basic protein composition and metabolism. Include the following analogy (A model train can be used while talking about this analogy):

  • A train is composed of many cars attached to an engine. Protein is made up of smaller parts called amino acids.
  • Phenylalanine is an amino acid.
  • When a train reaches a station, the cars are separated and attached to other engines where they can be taken to different stations. When protein is eaten, the amino acids are separated and are carried in the blood to different parts of the body.
  • If a car from a train is not hooked up to a new engine when it reaches the station, it cannot be taken to a new station, and cars pile up at the old station. An amino acid that doesn't get carried through the blood to other parts of the body will build up in the blood. (Relate this to the amino acid phenylalanine and PKU.)

Construct "The Protein Train"
Each child will construct his/her own model train, called The Protein Train, out of milk cartons. Encourage them to be creative with the provided materials. Instruct them to label one car as the phenylalanine car.

Using the train analogy encourage the children to use their own model trains to relate what happens to protein when it is eaten and what happens to phenylalanine in people with PKU. What happens if he/she eats a lot of protein or a protein with lots of phenylalanine? ( The Phenylalanine builds up in the blood.)

Distribute the worksheets. Give the children time to complete the first worksheet, then discuss the answers together. Continue with the second worksheet, as time permits.



  • model train with detachable parts
  • paper models of stations
  • for constructing the model trains you will need: milk cartons, construction paper, string, glue or stapler, cardboard rolls from toilet paper or paper towels, scissors, markers or crayons, cardboard circles for wheels
  • acrobat reader logo Worksheet 1
  • acrobat reader logo Worksheet 2


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