Now that I’ve finished my biochemistry and microbiology course, I’m no longer performing endless protein assays which require so much pipetting that you leave the lab with your hand seized up in to a crab claw because you’ve been holding a Gilson for two and a half hours. If you study biology, you will no doubt make acquaintances with Gilsons fairly early on in the year. This, my friends, is a Gilson pipette.
They come in a few different sizes and use very fine pipette tips to measure very small amounts of liquid (usually less than a millilitre). They have a dial on the top which you have to turn to set the volume you want to draw up and you have to depress the plunger before you put the tip into the liquid and then release it or you end up sucking stuff in to the barrel. One of your first labs will involve practicing this with water. If you learn nothing else from biochem and microbiology labs, do not depress the plunger in the liquid. This will be drummed in to you relentlessly. A lot. You don’t want to accidentally suck enzyme into the barrel which will then cause bubbles in the tip, so making the volume of anything else you pipette inaccurate and ruining your assay,
as I may have done in one of my first labs. In any case, I’ve left the Gilsons behind in order to play with E. coli and yeast. FUN.
The first two labs of my cell biology and genetics course have involved practicing sterile culture technique and performing a bacterial transformation of E. coli using pGLO. Transformation using pGLO is something that you may have done at A Level. I know that I did it but I can’t remember how it fit in to the syllabus, I think we just thought it was cool to make bacteria that glow in the dark. pGLO is a genetically engineered plasmid (circular DNA structure found in bacteria) which contains a gene for Green Fluorescent Protein (GFP – a protein isolated from jellyfish that glows green under UV light) and also a gene for ampicillin resistance. The gene for GFP is under the control of a modified arabinose operon. An operon is a basically a unit of linked genes which together control the expression of other genes for protein synthesis. The arabinose operon works by a regulator protein (araC) binding to a certain area of the operon which prevents the expression of genes which code for proteins responsible for arabinose digestion (arabinose is just a type of sugar). If arabinose is present, it binds to araC which causes a shape change that makes it easier for RNA polyermase to bind to the gene sequence and start transcribing the genes responsible for arabinose digestion. Pretty clever right?
In the pGLO plasmid, the genes which code for arabinose digestion have been replaced by the genes which code for GFP which means that if the E. coli have successfully taken up the plasmid, they will glow green under UV light on a petri dish containing arabinose! In the lab, we cultured E. coli on to several different types of agar plates – some containing arabinose, some without arabinose, some with arabinose and glucose – to see how the different nutrients we applied affected the expression of GFP. Interestingly, if there is glucose present in the cell then the arabinose operon is repressed. It is much easier for the bacterial cell to use glucose as a carbon source, so there is need for the arabinose digestion genes to be expressed. Therefore, we didn’t get any expression of GFP on the plate which contained arabinose and glucose.
It was a very simple experiment but what I love about biology is how something that superficially seems very straight forward (GFP expressed in the presence of arabinose but not in the presence of glucose. SIMPLES.) has such a highly regulated and delicate control system to ensure that the cell makes the best use of the nutrients available to it. Cells are incredible when you consider that there are hundreds of mechanisms like this in every area of the cell to control different pathways. The cell is an absolute power house, and yet they are the smallest building block of the human body. Looking forward to getting deeper in to this course!
Stay sciencey friends (and have another cell bio joke to end with)