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Cell-Free Protein Synthesis: Steps & Applications

Instructor: Stephanie Gorski

Steph has a PhD in Entomology and teaches college biology and ecology.

In this lesson, we'll talk about protein synthesis, particularly cell-free protein synthesis. We'll discuss why scientists like to make proteins without cells and how they do it.

Proteins

You probably know that your DNA codes for all those complex things that make you, you! What exactly does DNA code for? Protein! Your body's DNA template makes another, short-lived RNA template. This RNA template makes proteins. That's it! So you might guess that if proteins are what your DNA builds, they must be pretty important and we must be able to use proteins for all kinds of things. You'd be right!

DNA makes RNA makes protein.
DNA makes RNA makes protein.

Protein Synthesis

Sometimes people want to make proteins for scientific, medical, or industrial purposes. They could accomplish this by finding an organism that makes the protein they want, growing a bunch of that organism, and then purifying the protein from its cells. Or they could genetically modify bacteria to produce their protein, and then grow a bunch of these bacteria in a vat. Sometimes, that's exactly what people do. But using a living organism as a factory has its downsides. For instance:

  1. Living organisms take too long to make proteins, because they have to engage in the other biological processes of life.
  2. Living organisms aren't always terribly efficient at making proteins, because they have to busy themselves with the other processes they need to live.
  3. Living organisms must be kept at a constant temperature that is conducive to life.
  4. Some proteins are toxic to living cells, especially in high concentrations. What if we want to make a protein that is toxic to cells at high concentrations?
  5. You can't open up a cell to check and see how things are going without killing the cell.

This is when cell-free protein synthesis, also known as in vitro translation, can come to the rescue. Cell-free protein synthesis isn't a cure-all, however. Often the DNA that codes for the proteins we want to make will degrade quickly in cell-free protein synthesis. Scientists are currently working on improving the yield of cell-free protein synthesis without allowing the DNA to degrade.

Recently, scientists have become interested in amino acids (the building blocks of protein) that don't occur naturally. What if we want to make a protein that occurs with non-natural amino acids? Cell-free protein synthesis is a good way to explore these amino acids.

Scientists who want to label proteins to better use them in nuclear magnetic resonance, X-ray crystallography, or other visualization techniques find cell-free protein synthesis useful. Scientists who want to synthesize lots of different proteins to study their function also find it useful. Vaccines can also benefit from cell-free protein synthesis, because we can synthesize virus-like particles. Exciting advances in personalized medicine suggest that cell-free protein synthesis can be used to make treatments individualized to patients. Cell-free protein synthesis can also be used for screening candidate drugs to treat diseases.

How Do We Make Proteins Without Cells?

Cell-free protein synthesis needs two things:

  1. Something that codes for the protein
  2. Something that includes the raw materials to make the protein.

Easy, right? The thing that codes for protein will be a sample of either DNA or mRNA. The 'm' in mRNA stands for 'messenger', and mRNA is what would transfer information from the DNA to the ribosome. The DNA or mRNA will be what gives the instructions for how to make proteins.

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