Electrophoresis and Nucleic Acid Synthesis

Question 1

What is the basis of Gel Electrophoresis?

Answer 1

• Opposite charges attract.
• DNA molecules are negatively charged.
• By passing an electric current through a gel medium, the DNA molecules travel from the negatively-charged cathode, to the positively charged anode.

Question 2

How are DNA molecules separated in gel electrophoresis?

Answer 2

DNA molecules separate by length by passing them through a gel.

Fibrils within the gel hinder the movement of larger DNA molecules.

Electrophoresis separates by size and shape, as it separates the molecules based on their mass/charge ratio.

Shorter strands move faster, and appear at the bottom of the gel. Longer strands move slowly and travel shorter distances.

Question 3

What is loaded into the electrophoretic gel?

Answer 3

Your DNA sample

Dyes to help visualise the loading of your DNA into the well.

Dyes for tracking electrophoresis.

Glycerol/glucose/urea to increase the density of your sample, so the sample layers at the bottom of the well.

Question 4

What is the solid-phase synthesis of DNA?

Answer 4

• To perform each step of DNA synthesis in solution would require purification at each stage.
• Solid-phase synthesis requires attaching one end of the strand to a solid support (glass or polystyrene) which allows the excess reagents and side products to be washed away.