Golden Bread

Explore the science, engineering, and bioethics of a yeast that's genetically modified to make a vitamin-enriched food

This lab focuses on a vitamin-enriched strain of baker’s yeast that produces β-carotene, the nutrient that is converted to Vitamin A in the body. These genetically engineered yeast turn bright orange when they make β-carotene. Unexpectedly, not all the yeast are orange. Sometimes they grow as red, yellow or white colonies. The Golden Bread labs investigate this instability in the yeast, and challenge your students to improve the strain’s performance. Lab activities that include PCR, yeast transformation, and codon shuffling and quantitative analysis of data.

BACKGROUND

Relevant content and skills

Content

DNA Basics: what it is and how it works
Gene Expression: Transcription, Translation, Operons
Recombinant DNA: PCR, gel electrophoresis, cloning, selection by complementation

Skills

Pipetting
Transforming Yeast
Interpreting Data
Generating Hypotheses
Basic microbiology skills: Culturing yeast, Aseptic technique

SOME LAB MATERIALS TO HAVE ON HAND

HARDWARE: Some basic biology laboratory equipment such as glassware, pipets, a water bath or heat block to heat samples, an icebucket or styrofoam cup to cool samples, 4C fridge and ice-cold freezer (ideally to -20C) to store samples, a stir plate to mix samples, and an incubator to grow samples (though room temperature can work too). Some additional experiments might need a chemical hood, electrophoresis chambers, spectrophotometer, or a PCR machine.
CONSUMABLES: Some basic consumable laboratory equipment such as pipet tips, plastic tubes, growth media, petri dishes, toothpicks, spreaders, sterile loops, bleach or the like for decontamination and disposal of bioreagents. Some additional experiments might need additional consumables such as gel running buffers, loading buffers, stains to visualize DNA or proteins, cuvettes, PCR master mix, or an autoclave for sterilizing reagents.

RESOURCES AND DOWNLOADS

Specific materials for teaching this lab

CLASSROOM RESOURCES

READINGS

PPTs

VIDEOS

HANDOUTS

LAB RESOURCES

LAB MATERIALS

VIDEOS

Streaking Cells

PPTs

OTHER RESOURCES

INTERPRETING THE ENGINEERING RESULTS

A starting place for analysis and feedback

Download the teacher’s version of the lab manual for MUCH more information about the experimental outcomes, as well as pre- and post-lab questions to assess student understanding.

Briefly summarized:

If the white colonies of engineered yeast you used in this experiment have all the pathway components except a functional crtYB enzyme, then the addition of the crtYB* plasmid should restore the full pathway and return the cells to orange.

The negative and positive control can also help to interpret unexpected data. For example, if cells are growing on the negative control then there is a contaminated reagent (cells, media, plates, reagents).

In our experience, most but not all the colonies transformed with crtYB* are orange. There are many sensible interpretations of this data, all of which would require more experiments to investigate.