BioBuilding: Synthetic Biology for Students: Lab 5

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Lab 5: Golden Bread

  • Engineering reliability into an unstable genetic system may or may not make it a robust and profitable food source.

Acknowledgments: This lab was developed with materials from the Johns Hopkins 2011 iGEM team, as well as guidance and technical insights from BioBuilder teachers around the country



  • Define and properly use molecular genetics terms: PCR, gene expression, codon shuffling.
  • Explain the role of redundancy in synthetic biology and engineering.
  • Conduct PCR and TLC and interpret the results each.
  • Compare two engineering solutions to a given problem (redundancy vs kill switches)


One goal in the synthetic biology community is to convert scientific discoveries into practical solutions that meet real world needs. The world’s needs are many -- our population is aging, we’re putting increased pressures on our environment and there are widening economic inequalities -- but biology is a challenging material to work with. Our understanding nature is incomplete and evolving. Our tools for engineering it are primitive. Biology is not perfectly predictable. And as a society we’re often awkward or misguided when we interface with emerging technologies. We’d like to use our powers for good, to benefit all people and the planet. But what a complex challenge that is!

Background on Vitamin A production

"Nature is a masterful and prolific chemist" [doi: 10.1128/​MMBR.69.1.51-78.2005] and many laboratories work hard to mimic even the smallest bit of nature's range and skill. In this experiment we'll examine the biosynthesis of a carotenoid, a member of the isoprenoid family of chemicals that is responsible for many of the vibrant colors seen in plants and animals. Nature makes it look easy! There are more than 600 natural carotenoids, playing important roles in harvesting light for photosynthesis, as anti-oxidants to detoxify reactive species, and as regulators of membrane fluidity. The color of the carotenoids is directly related to their structure, in particular the number of conjugated double bonds. A minimum of 7 conjugated bonds is needed for any color so cis-phytoene with only 3 is colorless while trans-neurosporene with 9 is yellow, and lycopene with 11 is red. The structure of carotenoids makes them lipophilic so in the lab they're more soluble in organic solvents like acetone than they are in water. We'll exploit this fact when we measure the beta-carotene in a collection of cells that we'll grow.

chemical structure of two carotenoids
chemical structure of two carotenoids
Plants can make their own carotenoids from scratch, but animals can't so we must eat all we need. Think of the bright orange color of carrots and you're thinking of the isoprenoid they make called beta-carotene. Cut beta-carotene in half and add a water molecule and you have Vitamin A ---which is why parents tell their kids to eat their vegetables. And why developing countries that have limited food supplies have high incidents of disease due to vitamin deficiencies. For example, between at least 250,000 children in the developing world go blind each year due to Vitamin A deficiency. It's a huge problem but not a new one. As we start this "Golden Bread" module, you may want to consider existing biotechnology approaches to this issue, including the story of "golden rice" and the social impact of GMOs in the US and in Europe.

Image:Metabolic Pathway for b-carotene.png If synthetic biology is successful, then it will be possible to quickly and easily build biological technologies that improve health, provide sustainable energy or ensure a reliable global supply of food and water.


Part 1: Testing Genetic Variability

  1. Yeast will arrive on a YPD plate to grow at 30°C or room temp and stored at room temp or in the fridge.
  2. Identify color variants and restreak onto fresh YPD. Are there differences in the stability of the phenotypes? Are there growth conditions that make the colors more or less stable?
How to restreak cells

A video showing you how to restreak cells is here.

  1. Label your new petri dish with your initials, today’s date, the kind of media in the petri dish and the strain that you’ll be restreaking onto it.
  2. Start by dabbing the flat end of a toothpick onto a colony of yeast or bacteria that you want to restreak. The colony should be well isolated from the others and uniform in appearance.
  3. Transfer the cells from that toothpick by lightlying touch the toothpick to a spot on the new petri dish that you’d like to grow. Note: you should not break the surface of the agar with any of this procedure, but the results will still be OK, even if you do.
  6. Replace the lid of the petri dish and incubate the plate media-side UP in an incubator (ideally 37° overnight for bacteria, 30° 2 days for yeast).

Part 2: PCR

  1. Move Edvotek PCR bead to tube that fits in your PCR machine (or don't move the bead if the tube it comes in fits just fine)
  2. Thaw primer pair NO302 and NO303. These amplify the crtYB gene ORF.
  3. Prepare lysate: scoop a small colony you'd like to study into 50 ul H2O and microwave for 15 seconds with the lid of the eppendorf closed. Prepare lysate for any yeast you'd like to study.
  4. To the bead that's in the PCR tube add
    • 20 ul H2O and then vortex the sample
    • 1 ul of each primer
  5. PCR cycle:
    • 95° 2 minutes
    • 95° 20 seconds
    • 50° 20 seconds
    • 72° 2.5 minutes
    • repeat steps 2-4 a total of 35X
    • 72° 10 minutes
    • 4° hold
  6. Add 5 ul loading dye to each sample

Part 3: Yeast Transformation

Part 4: Measuring Vitamin A

Part 5: Baking Bread

Next day

In your lab notebook, you will need to construct a data table as shown below. These may be provided. Also be sure to share your data with the BioBuilder community here.

Lab Report

I. Introduction

  • Provide a brief introduction describing the field of synthetic biology.
  • What is a ___? How does this ___work? How might ____ be useful?
  • What is the role of the redundancy?
  • How does redundancy affect the expression of a genetic system?
  • How might synthetic biologists ___?
  • Why is it important to engineer a ___?
  • What are the advantages/concerns of engineering ___?
  • How might we test for the differences that the redundancy that may affect a genetic system?

II. Methods

  • You do not have to rewrite the procedure.
  • Explain why you did each step of the protocol.

III. Results

  • Present the data tables in clear format.
  • Present drawings of each slide.
  • Describe the results: Describe the appearance of the gel and the TLC plate. Are the bands and spots different?

IV. Discussion

  • Draw a conclusion: Do the ____ produce the same results in different chassis? Justify your answer.
  • Analyze the data: Be sure to discuss how each part of the experiment and results adds to your conclusion.
  • Are we sure that the transformation worked? What do the controls that lacked plasmid tell us?
  • Discuss errors and other reasons for data variability.
  • Use your results to explain why it is important for synthetic biologists to fully characterize the chassis used in an engineered system.


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