Which statements about restriction endonucleases are true?
I. Each cleave DNA at the same site, but leave different fragment lengths.
II. Each recognizes 4 to 8 nucleotides, and cleaves at all sites containing the sequence.
III. Approximately 1000 restriction endonucleases have been isolated and characterized.
IV. Each cleaves the DNA strand by reducing the base off at the sugar 1' position.

Question

Quizplus · Accepted Answer

Statement I is incorrect because different restriction endonucleases cleave DNA at different sites. Statement II is partially correct, as restriction endonucleases recognize a specific sequence and cleave at specific sites within that sequence. Statement III is correct, as approximately 1000 restriction endonucleases have been identified and characterized. Statement IV is incorrect, as restriction endonucleases cleave the sugar-phosphate backbone of DNA, not the bases themselves. Therefore, the only correct statements are II and III, making choice C the best answer.

Which Statements About Restriction Endonucleases Are True