Electrophoresis

Question 1

What is electrophoresis?

Answer 1

A procedure that uses an electrical current to separate out DNA fragments, RNA fragments or proteins depending on their size

Question 2

Stage 1 of electrophoresis using samples of fragmented DNA

Answer 2

Electrophoresis is commonly performed using agarose gel that has been poured into a gel tray and left to solidify
A row of wells is created at one end of the gel/

• put the gel tray in a gel bod or tank
• make sure the end of the gel tray with the wells is closest to the negative electrode on the gel box
• then add buffer solution to the reservoirs at the sides of the gel box so that the surface of the gel becomes covered in the buffer solution

Question 3

Stage 2

Answer 3

Take your fragmented DNA samples and, using a micropipette, add the same of volume of dye to each

Add a set volume of a DNA sample to the first well
(Make sure tip of your micropipette is in the buffer solution and just above the opening of the well, don’t stick the tip of micropipette too far into the well or you could pierce the bottom of it)
Then repeat this process and add the same volume of each of your other DNA samples to other well in the gel
Use a clean micropipette tip each time
Make sure you record which DNA sample you have added to each well

Question 4

Stage 3

Answer 4

Put the lid on the gel box and connect the leads from the gel box to the power supply
Then turn on the power supply and set it to tee required voltage e.g. 100V
This causes an electric current to be passed through the gel

DNA fragments are negatively charged, so they’ll move through the gel towards the positive electrode at the far end of the gel (anode)

Small DNA fragments move faster and travel through the gel, so the DNA fragments will separate according to size

Question 5

How to carry out electrophoresis with proteins

Answer 5

Proteins can be positively or negatively charged so, before they undergo electrophoresis, they’re mixed with a chemical that denatures the protein so they all have the same charge

Electrophoresis of proteins has many uses, e.g. identify the protein present in urine or blood samples, which may help diagnose a disease