During the preparation of a recombinant plasmid, a student uses agarose gel electrophoresis to verify the size of a digested DNA insert. Which of the following statements correctly explains the biophysical basis of this separation technique?
DNA fragments of different lengths possess varying charge-to-mass ratios; the agarose gel serves solely as a support medium to prevent thermal convection and diffusion during migration.
DNA has a constant charge-to-mass ratio; separation is achieved because the agarose gel acts as a molecular sieve that impedes larger fragments more than smaller ones as they migrate towards the positive anode.
DNA is positively charged due to its nitrogenous bases and migrates toward the negative cathode, with smaller fragments moving faster because they navigate the gel pores with less frictional resistance.
Larger DNA fragments carry a greater net negative charge than smaller fragments, which provides a stronger electrostatic pull that allows them to migrate faster towards the positive anode.
39 exam-style questions on OCR A A Level Biology Cloning and biotechnology. Each one has a worked solution and a mark scheme showing where the marks go.