Ever watched CSI or forensic files and seen a scientist using some machine to find a DNA match? That machine was likely a gel electrophoresis machine, one of the most interesting and all-encompassing biotechnologies! It doesn’t just use one biology, but chemistry too! Gel electrophoresis, or GE, also uses many properties of DNA to its advantage! Let’s get into it…
Before DNA is put into the machine, another biotech tool is used: restriction enzymes. What’s an enzyme? Well, it’s a protein that’s used to break a molecule, called a substrate, into smaller pieces. Enzymes attach to certain spots on the substrate and break it at those areas. This is what happens when your stomach breaks down starches and fats. Restriction enzymes work similarly, by binding themselves to certain areas of DNA. These areas are the same in every person and are a small sequence of bases. So, the initial sample is mixed with a certain restriction enzyme, or RE. All the other samples are mixed with the same RE. The key idea here is that since every person is different, the segments that the RE chops the DNA into will be differing in length.
Then, the samples are put into the GE machine slots, which are filled with agarose gel. This allows the DNA segments to move easily. But how are they moving? Well, DNA is a negatively charged molecule, meaning it would be attracted to anything positive. So, the opposite side of the machine has a positive current which will attract the segments. Remember how the segments are all different lengths? Well, shorter segments move through the gel faster than longer segments. After a certain amount of time, the current is turned off and the DNA pieces stop moving. Then, you’re left with an image like this:
Via Labnet International: https://www.labnetinternational.com/blog/2018/04/brief-history-electrophoresis
The bars represent a DNA segment. If two DNA segments are at the same area in two samples, it means they are related. The more segments that share spots means that they are more and more closely related. Scientists use this to compare an unknown sample with known samples in hopes of finding a match or relatives of the unknown person! This tech isn’t brand new but it’s still amazing to see such an interesting combination of ideas.
Although gel electrophoresis is common in crime investigation, it can also be used to determine victims/witnesses of a crime and possible family members/parents. It’s very conclusive and rarely faulty due to the precision of restriction enzymes! It can also be used in combination with the polymerase chain reaction, or PCR. Watch this video by the Amoeba Sisters to learn about PCR!
What are your thoughts? Do you have any suggestions for a future “What and Why” post? Let us know!
Sources:
Labnet International: https://www.labnetinternational.com/blog/2018/04/brief-history-electrophoresis
National Institutes of Health: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4846332/
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