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Status: student
Grade: 4-5
Location: Outside U.S.
Country: Malaysia
Date: Fall 2013

How does agarose gel electrophoresis determine the molecular weight of DNA?

Hi Nadia, You can imagine agarose gel to be like a twisty, curvy network of caves, and the DNA molecules as different sizes of travelers in the caves.

If you're a person, it might take you a very long time to walk through them because you might squeeze through one hole or have to find a way around a hole that's too small. On the other hand, a mouse might move through very fast, because the mouse can fit through more holes! And, air (which is made up of VERY small particles) can move through easily!

Big molecules of DNA move more slowly just like the people in the example. Smaller molecules of DNA move faster just like the mouse. And tiny pieces of DNA move fastest of all (like the air) because they are

Hope this helps, Burr

Hi Nadia, Electrophoresis can be used to determine the molecular weight of a piece of DNA. DNA is negatively charged when it is in a neutral environment. When a current is run through a gel a piece of DNA will be drawn towards the anode (the positive end). Larger pieces travel more slowly than smaller pieces. A scientist can find the molecular weight of a piece of DNA by comparing it to other pieces of known molecular weight. I hope this helps.

Andrea Kirk Ph.D.

Biologists often use a technique called agarose gel electrophoresis to separate molecules of DNA. Because DNA is negatively charged, DNA molecules will migrate through a gel towards the positively charged end of the gel when an electric field is applied. Shorter molecules travel more rapidly through the pores of the gel than longer molecules which tend to get trapped more often. You can get a good estimate of the size of a DNA molecule by comparing the distance it traveled to DNA of known molecular weight.

Separating DNA on an agarose gel is a very basic and commonly used technique for biologists - it can be used to help put new combinations of DNA together to understand what genes do, or in a forensics lab to analyze the content of a person's DNA to figure out who did the crime!

Hope that helps! Ethan

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