This set of Molecular Biology Multiple Choice Questions & Answers (MCQs) focuses on “General Properties of Plasmids”.
Explanation: The plasmid is an autonomous replicating genetic material. It has its own origin of replication and complete replicating machinery thus can replicate freely and is thus independent of the replication of the host genome.
2. How the plasmid clones can be screened?
a) By selectable markers
b) By bacterial resistance gene
c) For restriction site
d) By ARS sequence
Explanation: Plasmid contains a selectable marker that allows cells that contain the vector to be easily identified. Thus selectable markers are used to screen clones.
3. How many restriction sites are contained by a plasmid?
d) More than 1
Explanation: Plasmid has one or more than one site for one or more restriction enzymes. Artificial plasmids contain single restriction site for one or more restriction enzymes. This allows DNA fragments to be inserted at a definite position.
4. Who were the scientists who discovered the plasmid pBR322?
a) Rodriguez and Bolivar
b) Joller smith
c) Herbert Boyer
d) Stanley Cohen and Joller smith
Explanation: Plasmids are most commonly used as vector DNA. pBR322 is a plasmid vector discovered by Rodriguez and Bolivar in 1977.
5. Under relaxed condition how many copies of plasmid are present in the cell?
a) 10 – 100 copies
b) 100 – 500 copies
c) 1 – 300 copies
d) 10 – 700 copies
Explanation: Most plasmids used in molecular cloning are generally present under relaxed condition. They are normally present in 10 to as many as 700 copies per cell.
a) Less than 100 base pair
b) Less than 10 base pair
c) Less than 70 base pair
d) Less than 50 base pair
Explanation: Plasmid vector contains a strategically located short, less than 100 base pair long segments of DNA. This segment of DNA is known as polylinker segment.
7. The full for of pUC is polylinker university cloning.
Explanation: The E. coli derived plasmid.
8. The host bacterium takes up a plasmid in presence of ______________
a) Monovalent cations
b) Monovalent anions
c) Divalent cations
d) Divalent anions
Explanation: The host bacteria can take up a plasmid from its surrounding. This process is greatly enhanced by the presence of divalent cation such as Ca2+.
9. What is the temperature at which bacteria can takes up the plasmid?
Explanation: Bacteria efficiently take up the plasmid DNA at -42˚C. This increases cell membrane permeability to DNA.
10. Which gene in the pUC18 vector confers antibiotic resistance to the transformed cells?
Explanation: pUC18 is a well known cloning vector. It contains the AmpR gene that confers resistance to the antibiotic ampicillin which is used as a selectable marker.
11. What is the characteristic of lacZ gene of pUC18 vector among the following?
a) Encodes for antibiotic resistance
b) Encodes for β-galactosidase enzyme
c) Encodes for β-lactamase enzyme
d) Encodes for β-galactoside transferase enzyme.
Explanation: The lacZ gene of the pUC18 vector is a gene of the lac operon encoding for the β-galactosidase enzyme. This enzyme cleaves galactoside present in the medium as a carbon source and liberates a blue coloured product.
Explanation: Although pBR322 is the most commonly used vector in scientific research. pSC101 is the first engineered plasmid vector. The pUC family vectors are the derivative of the pBR family of vectors.
13. What is the expanded form of pBR in pBR322?
a) Plasmid Boliver and Rodriguez
b) Plasmid Baltimore and Rodriguez
c) Plasmid bacterial recombination
d) Plasmid bacterial replication
Explanation: pBR322 was the first artificial cloning vector developed in 1977 by Boliver and Rodriguez. Thus pBR represents its creators leading to the expansion- Plasmid Boliver and Rodriguez.
14. What is incorrect about plasmid?
a) Helps in reproduction
b) Contains stress resistant genes
c) Serves as the transformation vehicle
d) They are the genetic material of the bacteria
Explanation: Plasmids are the extra genetic materials that are found in the bacterial cell along with the genetic component. They are autonomously replicating cyclic double strand DNA molecules used as vectors for gene transfer and also for replication.
15. The repressor for the β-galactosidase gene is encoded by ___________
c) Lac I
Explanation: In the pUC family vector the gene Lac I encodes for the repressor protein. This protein binds to the promoter of the lacZ thus inhibiting the expression of the gene.
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