Curriculum ConnectionGrade 12 University Preparation (SBI 4U)

Strand D- Molecular Genetics

By Bassam El Masri | April 24, 2015

How to make a Lac Operon

USING DOLLAR STORE ITEMS

Specific Expectation

D3.3 explain the steps involved in the process of protein synthesis and how genetic expression is controlled in prokaryotes and eukaryotes by regulatory proteins (e.g., the role of operons in prokaryotic cells; the mechanism of gene expression in eukaryotic cells)

IntroductionAfter teaching DNA replication and protein synthesis (transcription and translation), students are expected to be familiar with the mechanisms that control gene expression. A commonly studied example, in prokaryotes, is the Lac Operon (inducible model) and/or the Trp Operon (repressible model).

The procedure that follows outlines the steps for a teacher to build a Lac Operon model in order to demonstrate to the whole class how an operon functions. Students should be given time in class to look closely at the model themselves and manipulate it in order to better grasp the concept and be able to complete the assignment which follows.

Follow-up Activity The students are assigned the task of creating a Trp Operon model, using

similar or different materials as the ones used for the Lac Operon. The teacher should encourage creativity and allow students the opportunity to research and explore independently.

Ideally, students would be working in pairs and given a week to complete the project.

Students would then present their models to the whole class or in small groups and demonstrate how their model works.

Such a project offers the students an opportunity to work in small groups/pairs which allows them to experience cooperative learning and self-regulation to meet deadlines.

Lastly, this project can be used as an assessment tool. A teacher can tailor a rubric that meets the needs of the students in order to assess their understanding of the concept, presentation skills, and designing capabilities.

Safety Concerns Be careful while using the knife cutter. To avoid scratching surfaces, use the

back of a cardboard or wooden clipboard while cutting the foam sheets. If using glitter glue, use it at the very end and allow time for it to dry to avoid

staining clothes and other surfaces.

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Material

1 large cardstock paper 28 x 22 inches (light colour) Foam sheets ( variety of colours) Velcro strips Brass split pins Sharpie coloured markers Ruler Scissors and cutter knife Glitter glue (optional for design)

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Methodology1. Start by cutting a strip of the card stock paper (4 x 28 inches). Using a ruler

and a Sharpie, draw perpendicular lines to create sections for the different genes that constitute the operon.Label the sequence of genes as shown below. Ensure the operator gene is long enough so that the repressor molecule can fit within its boundaries

2. Using a foam sheet, draw and cut out an oval shape with extending flaps as shown below. Stick two pieces of Velcro at the end of the flaps so it can be fastened into a loop. This will be the RNA polymerase.

3.

Using a different coloured foam sheet, draw the shape as shown below. Cut the foam sheet in half and stack the two halves together to cut two shapes simultaneously. Use the knife cutter for sharp corners and cleaner cut edges. Place the two pieces facing each other (mirror image) and overlap them in the middle section. Insert the copper split pin in the centre as shown to hold the two pieces together. This will be the repressor molecule.

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Finally, place two pieces of Velcro at the back of the top flaps and match the Velcro pieces to their location on the operator gene of the operon as shown below.

4. Use a third colour foam sheet to draw and cut out the shape shown in orange below. Ensure that the flap fits into the square-shaped gap at the bottom of the repressor molecule. Allow some additional space on top of the flap to stick a piece of Velcro. This will be the inducer molecule (allolactose). At the back of the repressor molecule, just above the square-shaped gap, place the matching piece of Velcro to create a perfect fit.

The combination of both molecules represents the repressor-inducer complex which can be rotated around the pin to show a configurational change when the binding takes place as shown below.

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5. Now label the molecules using the coloured Sharpies of your choice. Make a small diagonal cut at the bottom corner of the right half of the repressor molecule to allow you to write and reveal the prefix (in) to indicate the in-active configuration of the repressor molecule.

6.

Finally, slide in the RNA Polymerase molecule in the gene strip and the model is complete.

Summary of action: The regulatory gene produces the repressor molecule (blue). In the absence of Lactose (allolactose), the repressor molecule is

active and binds to the operator. The repressor stops RNA polymerase (which binds to promoter) from transcribing the structural genes.

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When Lactose (allolactose) is present in the cell, it binds to the repressor causing a configurational change which makes the repressor-inducer complex detach from the operator. This in turn allows RNA polymerase to proceed along the operon and transcribe the structural genes.

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