• Question: where do the crystals come from ?

    Asked by anon-185566 to William, Rebecca, Martyna, Callum, Alice, Adam on 6 Nov 2018.
    • Photo: Alice Loasby

      Alice Loasby answered on 6 Nov 2018:


      This depends on what you’re trying to crystallise. With proteins, we express and purify them so they are really pure with nothing contaminating them. They also need to be at a high concentration, usually around 10 mg/mL, in a buffer that they are soluble in. Then we use commercially available screens to set up crystal trays. The screens have conditions which proteins are known to crystallise in, there are different ones for different types of protein. We set these up and hope crystals will nucleate and grow!

    • Photo: Callum McHugh

      Callum McHugh answered on 6 Nov 2018:


      That’s a great answer from Alice.

      I’m interested in crystals from molecules smaller than proteins. Basically a crystal is a solid material where the molecules interact in a highly ordered manner in all dimensions. Our crystals are grown from solutions of the molecules, usually by evaporating the liquid slowly. This increases the concentration of the molecules in solution to a point where the solution is saturated. At this point the molecules begin to precipitate from solution to give a solid. If we do this under the right conditions and slowly enough the molecules will nucleate (arrange themselves in the correct way to form the structure) and grow to give larger crystals.

    • Photo: Rebecca Roddan

      Rebecca Roddan answered on 7 Nov 2018:


      Protein crystals come from trying to precipitate it in a nice way that gets it to crystallise. By precipitate, we basically mean trying to get it to ‘crash out’ of solution. So your protein is dissolved in a mixture of water and some other molecules, we then use methods to evaporate some of the water so that the protein becomes more concentrated in the solution. Eventually, when lots of the water has evaporated, the protein is no longer able to dissolve and so it ‘crashes out of solution’ appears as a solid. We try this with lots of different water and ‘other molecules’ solutions to hope that we find a condition which lets our protein form a crystal when it crashes out.

    • Photo: Adam Berlie

      Adam Berlie answered on 7 Nov 2018:


      Everyone above has given a really nice description of crystallisation. I’d just like to point out that you can also crystallise or form crystals as liquids freeze or turn into solids. This can be by decreasing the temperature or applying pressure. One example would be water turning into ice, this can be thought of as a type of “crystalisation”. I once took some benzene which is a liquid at room temperature and put it between two diamonds to do some research. As you squeezed the diamonds together very carefully, you could see the benzene went from a liquid to solid crystals. It’s all about the changing interactions between the molecules themselves which ae important!

    • Photo: Martyna Pastok

      Martyna Pastok answered on 14 Nov 2018:


      Depends what you are crystallising. Crystal is a very ordered thing built from many repeats of the same molecule – blocks.

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