7.2.3 Electrophoresis: Separating DNA

Question 1

electrophoresis

Answer 1

• separates DNA segments based on their rate of movement through a gel under an electric field. This rate of movement is related to the size of the DNA segments
• Under an electric current, small molecules will travel through the gel more easily (and therefore faster) than larger molecules.
  • Electrophoresis provides scientists with a valuable tool for studying molecules such as DNA, RNA, and proteins.
• a method used to separate DNA segments on the basis of their rate of movement through a gel under
  an electric field.
• DNA has an overall negative charge. A DNA mixture is placed within a well of an electrophoresis gel (as seen in the diagram to the left). The gel is within a box filled with a buffer solution. Electrodes on opposite ends of the box form a current, which causes the DNA mixture to travel from the negative electrode (the cathode) down through the gel towards the positive electrode (the anode).
• As the DNA travels down the gel, segments separate based on size. Large segments move more slowly through the gel than smaller segments. The resulting gel will have bands on it that represent DNA fragments of a particular size.
• Electrophoresis can reveal much about the molecules in a particular mixture. The illustration to the left shows the bands resulting from the separation of various plasmids exposed to restriction enzymes. Comparing the bands of DNA, we find that the original plasmids must have differed in size.

Question 2

The purpose of the comb in gel electrophoresis is

Answer 2

• to create the wells into which the samples of DNA will be put

Question 3

Two samples of the same plasmid, treated with two different restriction enzymes, are run on the same gel. We observe that one sample separates into two bands and the other sample into three bands. What conclusion might be drawn?

Answer 3

• The plasmid has two restriction sites for the first restriction enzyme and three for the second one

Question 4

Which of the following is not true about the gel electrophoresis of DNA?

Answer 4

• Separation of the fragments is influenced primarily by the magnitude of the charge on the fragments.

Question 5

The overall charge of DNA is influenced by the __________ of each nucleotide, and is __________.

Answer 5

• phosphate group, negative

Question 6

Electrophoresis is used to

Answer 6

• separate macromolecules on the basis of size.
• separate macromolecules on the basis of shape.
• separate macromolecules on the basis of electrical charge.
• all of the above