agarose gel.
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Electrolysis works on the basis that DNA has an overall negative charge. It is repelled by another negative charge, and attracted to a positive charge.
Before you run an electrolysis, you use an enzyme called a Restriction Endonuclease, which cuts DNA at specific Base pair sequences. Since each person (or any other organism)(and besides identical twins) has unique DNA, this Restriction Endonuclease will cut everyone’s DNA into different sized pieces.
Now, to run an Agarose gel, you have a plate with the agarose on it, and two differently charged electrodes near each end. At the end with the negative electrode are “wells” in the agarose that you put your DNA samples into, and because of DNA’s negative charge, it will be repelled away from that negative electrode and attracted to the positive electrode on the other end of the agarose.
The agarose gel itself works like a sieve or a filter: it lets the smallest pieces of DNA through the easiest, and the bigger ones take longer to get through. So, by the time you turn off the electricity, the DNA (which you’d need a dye to see) ends up in bands based on size (the smaller ones went faster and are closer to the positive end, the bigger ones went slower and are by the negative end), and since each each person has different DNA and different numbers and sizes of pieces, each person’s DNA will make a different band formation.
The phosphate unit in a deoxyribonucleotide is negatively charged. In Agarose Gel Electrophoresis, there are two terminals: the negatively charged one and a positively charged one. The negatively charged terminal is placed nearer to the wells where the DNA fragments are inserted together with a gel-loading dye using a micropipettor, and the positively charged one at the end of the gel, so that when the power supply is turned on the DNA fragments will begin to be attracted away from the wells, in the opposite direction, towards the positive charge.
This is because like charges repel each other, but opposite charges attract. This is also why when DNA is extracted, we use a glass rod to get it out, as the glass rod is positively charged too.
Remember that Agarose Gel is a retardant gel, which means it slows things down. It has many tiny little pores, so that the larger fragments of DNA will go more slowly, and the small fragments of DNA are able to go through faster. After the electricity has been turned on for some time you’ll see smaller fragments further away from the well, and larger fragments nearer to the well.
And no DNA is not always cut using enzymes, for example in the Polymerase Chain Reaction a specific region of DNA can be copied, so that the presence of a gene can be detected, such as that of a virus that may have attacked you, or to see if you have a genetic disease in which your gene has been deleted, replicated or if the nucleotides in it are less/ more than usual. Some examples are DMD (Duchene’s Muscular Distrophy) where some of the exons, which are parts of one gene, are missing, Huntington disease in which your huntington gene is larger than usual, or detection of the virus causing AIDS.
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