GEL-electrophoresis
THE GEL
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HOW DOES GEL-ELECTROPHORESIS WORK?
ACTIVITY To help students understand how the different fragments of DNA migrate on the gel, you can do the following kinesthetic activity with them. You will need to create two identical obstacle courses that students need to maneuver through. Ask two students to link together either by holding hands or tying them together with a string. Make another group with 5 to 7 students and link them into a human chain. With a timer, ask both groups to work through the
obstacle course. You will find that the pair will finish the course faster than the group of students. This activity reiterates that the longer the fragment, the longer it will take to migrate through the pores of gel. |
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THE PROCESS
- Using direct current, a negative charge is placed on the side contaning the sample and a positive charge on the opposite side
- DNA solution will migrate towards the positively charged electrode (opposite charges attract)
- The migration will allow for the separation of the DNA fragments of different size
- The gel is stained with Ethidium Bromide. The stain inserts itself into the DNA and fluoresces under UV light. (Note that students should be aware that Ethidium Bromide is carcinogenic)
- The size of the fragment is then determined using a molecular marker as a standard
- The standard contains fragments of known size. The distance of each band made by the standard is measured. The data is plotted on a graph using the log of the known fragment size versus it's migrated distance. This graph is then used to interpolate the size of unknown fragments after their migrated distance is measured.
- compare fragment sizes from different sources
- can also be used with proteins (polyacrylamide has smaller pores and is used for the smaller molecules
- the gel containing the fragment of interest can be excised and purified for future
use
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The following activity can be used as a consolidation activity after the lesson with your students. The activity asks the students to match the DNA of three babies to their rightful parents. Students should have learned that DNA of an offspring consists 50% of DNA from each parent. Using this previous knowledge, students should be able to identify that the baby should have bands from both parents. The first document can be printed and given to students with only instructions to match the babies to their parents. The second document contains additional questions for you to work through with your students after the activity.
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