Clever Solution for Plasmid Restriction Digestion Puzzle

What are the expected sizes of restriction fragments following complete digestion for a plasmid with specific restriction sites?

Choose the correct option:

A. 400, 1000, 1200, 1400

B. 200, 1600, 2200

C. 200, 600, 1800, 2800

D. 200, 400, 1000, 1200 (2 of these)

E. 400, 1200, 2400

Answer:

For the described plasmid with specific restriction sites, the expected fragments after complete digestion would be 400, 1000, and 1200 base pairs (with two occurrences of the last), corresponding to option D.

Explanation:

Assuming a plasmid of 4000 base pairs with restriction sites at 200, 600, 1800, and 2800, the expected sizes of the restriction fragments following complete digestion would be determined by subtracting each restriction site location from the next one in the sequence, with the last one subtracted from the total length of the plasmid.

In this case, after complete digestion, the fragment sizes would be: (600-200) = 400 base pairs, (1800 - 600) = 1200 base pairs, (2800 - 1800) = 1000 base pairs, and (4000 - 2800) = 1200 base pairs. Therefore, the sizes of the resulting fragments would be 400, 1200, 1000, 1200 in sequence, or as two repeated sizes: 400, 1000, 1200 (2 of these), which corresponds to option D given.