Matthew C. Bostick
Upper School Science Instructor
Westchester Country Day School, High Point, NC

September 2015

In this simple exercise, students create a translation product (a protein “necktie”) from mRNA instructions. This kinesthetic activity also serves as a wonderful lead-in for discussions of the central dogma of biology (DNA and RNA protein), factors that influence protein folding, and the genetic mutations that may influence the accuracy of protein synthesis.

Establishing roles and the objective

Divide students into groups of 3, and give each group a necktie. Have each student take on a different role, with one student representing DNA; one representing mRNA; and one representing the ribosome/tRNA complex. Explain that your classroom will represent the nucleus of the eukaryotic cell, and that the hallway will serve as the cytoplasm where protein synthesis occurs. The door to the hallway will represent the nuclear pore from which mRNA may exit to begin translation within the cytoplasm at the site of the ribosome.

Explain to students that their task is to correctly fold a necktie based on instructions from the student designated as DNA. However, DNA may not leave the nucleus (the classroom). Instead, a messenger (the mRNA student) must translate a copy of DNA’s instructions to the third student (acting as the ribosome/tRNA complex) who is then charged with folding the correct necktie (protein) according to the mRNA transcript.

Guidelines

Allow the student most experienced with tying a tie to act as the DNA macromolecule. Give directions to tie a knot, such as the Windsor knot. As DNA is nucleus bound, this student cannot leave your classroom. Instead, have the student serving as the mRNA transcript listen to DNA’s instructions for no more than a minute. Do not allow mRNA to physically copy the directions or view the images on the DNA (necktie) directions during this initial trial. 

Have the mRNA student leave the room and “translate” their version of the directions to the third student, designated as the ribosome/tRNA complex. The third student (located in the hallway cytoplasm) will attempt to tie a correct “Windsorase” necktie protein using only the verbal instructions from mRNA.

With any luck, the newly translated protein necktie will look awful. Because the protein has an incorrect shape, we may assume that it also performs an incorrect function. Use this moment to briefly introduce the central dogma of biology, protein structure, or even to explore genetic disorders.

Afterward, allow students to change their method for a more efficient, accurate flow of molecular information from DNA to mRNA to protein. Students may realize that mRNA needs to have an accurate working “transcript” to achieve correct protein translation at the ribosome. Allow students to copy or even to take a picture of the DNA directions for a more accurate information flow. Congratulate students when they correctly tie a Windsor and fold their protein accurately, thereby allowing the protein to function correctly.

To conclude the exercise

Remind students that their DNA necktie instructions served as a specific nucleotide sequence. Located in genes, these nucleotide sequences ultimately encode for a protein with a highly specific genetic function, such as the production of the normal hemoglobin molecule responsible for transporting oxygen in your red blood cells.

If you use this activity to teach protein structure and folding, you can ask students to tuck paper clips of different colors into the folds of their neckties. They represent the interactions between amino acid side chains—such as the covalent disulfide bridges that form between specific cysteine side chains to determine a polypeptide’s tertiary structure and shape.

The role of proteins in the cell

As vital macromolecules for living systems, proteins may be folded much like a necktie into polypeptides playing a range of cellular roles. They could function as enzymes, antibodies, or hormones. While transcription produces a single-stranded molecule of mRNA from a double-stranded DNA helix, the process of translation produces a highly specific sequence of amino acids, called a protein, from the order of nucleotide triplets specified by the mRNA transcript. Because this sequence is so specific, an error in the mRNA transcript could result in more than just a poorly folded necktie protein. For example, a single nucleotide error in DNA and the resulting mRNA transcript (such as a base pair substitution) could produce an incorrect sequence of amino acids, and therefore a dysfunctional protein. 

If you teach advanced biology classes or have an interest in differentiating your instruction, you may want to use the illustrative example of sickle cell vs. normal hemoglobin with this lesson. In sickle cell hemoglobin, a gene mutation results in the substitution of the hydrophilic amino acid glutamic acid by the hydrophobic amino acid valine in the beta chains of the hemoglobin molecule. This incorrect amino acid sequence—and the resulting incorrect polypeptide—drastically changes the shape of the molecule, rendering it less capable of transporting oxygen than a correctly folded, normal hemoglobin protein would be.