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Lab scissors continued --- Dr. Mary McMillan

In my last post I showed you my lab scissors – better known in the business as restriction enzymes.
So I thought I should follow up and show you what they do!
This is a picture of an agarose gel – used to separate fragments of DNA according to their size. Each glowing band on the gel is a group of DNA molecules all of the same size. In the lane on the left I have loaded a DNA ladder, which is a collection of DNA fragments of known sizes. We can use this like a ruler to measure the size of other fragments of DNA on the gel.
In the middle lane I have loaded one of my DNA fragments that hasn’t been exposed to my restriction enzyme. In the lane on the right I have the same DNA sample, except I have mixed the DNA with one of my restriction enzymes. The enzyme has cleaved the DNA, resulting in shorter fragments.
My main use for this technique is to look for genetic variation within certain regions of DNA. If there are changes to DNA, it can change the restriction sites, or places where the enzymes will cut DNA. Sometimes it will mean there is no longer one of these sites, and the DNA will remain uncut. Other times changes to DNA can change where the restriction sites are, moving them closer together or further apart, so that I get different size fragments after the digestion. By looking at the different patterns of bands on a gel like this I can figure out if different people have the same version, or different versions of a gene. So my lab “scissors” are pretty useful!

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Lab scissors by Mary McMillian

I thought today I would show you some of my lab scissors. Ok, I know that these probably don’t look like scissors to most people, but to a molecular biologist these are scissors for cutting DNA.
These are just a few of my restriction enzymes that I have in the lab. Restriction enzymes are cool little proteins that cut up DNA. Each of these enzymes here recognises different sequences in DNA, called restriction sites. When they find those sequences in a piece of DNA they will cut the DNA at that position. Some restriction enzymes cut straight through the DNA, leaving what we call a blunt end. Other enzymes make staggered cuts in the DNA, leaving single stranded overhangs that we call sticky ends.

This is particularly useful if you are a molecular biologist, because you can cut pieces of DNA from different sources with the same enzyme, and they will then have matching ends that can be stuck (or ligated if you want the technical term) back together. This is how we create recombinant DNA. In my case I often use restriction enzymes to cut some human DNA and some bacterial DNA, and then stick the two together so that I can get bacteria to express human genes.
PS. Stay tuned and in my next post I’ll show you how these restriction enzymes work in practise :) Thank you Mary, for explaining about the restriction enzymes. We look forward to your next post about the working mechanism of these scissors.

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