Which of the following statements regarding plasmid-cloning vectors is correct?
A)Circular plasmids do not require an origin of replication to be propagated in E.coli.
B)Foreign DNA fragments up to 45,000 base pairs can be cloned in a typical plasmid.
C)Plasmids do not need to contain genes that confer resistance to antibiotics.
D)Plasmid vectors must carry promoters for inserted gene fragments.
E)The copy number of plasmids may vary from a few to several hundred.

Question

Quizplus · Accepted Answer

Plasmid copy number can vary in different types of plasmids, ranging from a few to several hundred. Choice A is incorrect because all plasmids, including circular ones, require an origin of replication for propagation. Choice B is incorrect because small plasmids typically have cloning capacities of 1-10 kb, while larger ones can accommodate up to 50 kb. Choice C is incorrect because most plasmids used for cloning contain antibiotic resistance genes to select for transformed host cells. Choice D is incorrect because plasmid vectors do not necessarily need to carry promoters for inserted gene fragments, although many do for optimal expression.

Which of the Following Statements Regarding Plasmid-Cloning Vectors Is Correct