Which plasmid form migrates fastest?

Which plasmid form migrates fastest?

• A. Supercoiled form
• B. Linear form
• C. Nicked circle
• D. Multimer

Answer: (A)

DNA mobility in agarose gel depends on shape as well as size. The most compact form—supercoiled plasmid—packs its length into a tight, twisted structure, which reduces its effective hydrodynamic size and the friction it experiences as it moves through the gel matrix. That compactness lets it slide through the pores more easily and hence migrate faster than other forms. A nicked circle relaxes the twists and becomes a looser circular shape, increasing its effective size and friction, so it moves more slowly. The linear form, while still double-stranded, is less compact than the supercoiled form and also migrates slower. Multimers, being larger concatenations, behave like bigger DNA fragments and migrate even more slowly. So the fastest migrating form is the supercoiled one.

DNA mobility in agarose gel depends on shape as well as size. The most compact form—supercoiled plasmid—packs its length into a tight, twisted structure, which reduces its effective hydrodynamic size and the friction it experiences as it moves through the gel matrix. That compactness lets it slide through the pores more easily and hence migrate faster than other forms. A nicked circle relaxes the twists and becomes a looser circular shape, increasing its effective size and friction, so it moves more slowly. The linear form, while still double-stranded, is less compact than the supercoiled form and also migrates slower. Multimers, being larger concatenations, behave like bigger DNA fragments and migrate even more slowly. So the fastest migrating form is the supercoiled one.