This set of Cytogenetics Multiple Choice Questions & Answers (MCQs) focuses on “Plasmids”.
1. In which of the following will you expect plasmids to be absent?
a) Streptococcus sp
b) Schizosaccharomyces pombe
c) Panthera sp
d) Haemophilis sp
Explanation: Among the following options only prokaryotes and lower eukaryotes like yeast can have plasmids. So option a and d being prokaryote and b being yeast has plasmid. But option c being higher eukaryote i.e. the genus of tiger lacks plasmids.
2. Which of the following is not true about plasmids?
a) They are extrachromosomal DNA
b) They are double stranded
c) They confer antibiotic resistance
d) They may get incorporated in chromosome
Explanation: Plasmids generally don’t get incorporated in a chromosome; if it does so then it is known as episome not plasmids. It is true that plasmids are circular, double stranded, extrachromosomal DNA that can confer antibiotic resistance.
3. Which class of plasmids assists in the production of bacteriocins?
a) F plasmid
b) F’ plasmid
c) R plasmid
d) Col plasmid
Explanation: Col plasmids help in the production of cilicins and bacteriocins. This helps them to kill other bacteria. While F plasmids confer fertility and R confers resistance to some antibiotics.
4. Which of the following is not a part of RTF?
a) Origin of replication
b) Chloranphemicol resistance
c) Origin of transfer
d) Pilli forming gene
Explanation: The R agent class of plasmids consists of Resistance transfer factor RTF as well as Resistance gene R. While the origin of replication and transfer, and pilli forming gene are part of RTF; antibiotic resistance gene such as Chloramphenicol resistance gene is part of R.
5. In an experiment you want to express your gene of interest in a prokaryote through a plasmid. What would be your ideal copy number?
a) 2 or 3
Explanation: The gene of interest by us should always be expressed in low copy number as if it is in higher copy number t will use more of bacterial recourses without helping them at all. So, bacteria might then dispense some of these chromosomes.
6. Pilli forming gene is a must for plasmid transfer. State whether it is true or false.
Explanation: Pilli forming gene pilus gene is responsible for forming the cytoplasmic bridge pilli between the two bacteria. Without this the plasmid couldn’t be transferred to the other bacteria. Thus, it is really indispensible.
7. Which of the following antibiotic resistance is through alteration of uptake?
Explanation: Tetracyclin resistance is provided by some transporters that selectively transport tetracycline outside the cell thus providing resistance; whereas the other antibiotics are through other modes of resistance.
8. Which of the following plasmids fir the definition of episomes?
a) F factors
b) R factors
c) Col factors
d) RTF factors
Explanation: Episomes are the plasmids that can get incorporated in a central chromosome. F factors or fertility factor is one such plasmid.
9. Streptomycin resistance is conferred by______________
a) Modification of antibiotic
b) Modification of target
c) Modification of uptake
d) Using different insensitive pathway
Explanation: Streptomycin resistance is through the modification of the target i.e. Ribosome, so that it can no longer interact with streptomycin in the same way.
10. Bacteriocins are _______________
a) Toxic nucleic acids
b) Non-ribosomally synthesized toxic proteins
c) Ribosomally synthesized toxic proteins
d) Modified normal proteins
Explanation: Bacterocins are ribosomally synthesized proteins or peptides that are not toxic to the producer but to the other bacteria around it.
11. Bacteriocins are produced by bacteria in __________
a) Lag phase
b) Log phase
c) Transition phase
d) S phase
Explanation: In the S phase there is a lot of competition between the bacterias for space and resources. Bacteriocins are used to kill off the bacterias of same species or related bacteria to resuce the competition.
12. What is the general target of bacteriocins?
b) Plasma mambrane
c) Cell wall
Explanation: Bacteriocins have proteolytic and amylolytic enzymes that can digest the cell wall and kill the bacteria. It generally doesn’t target anything else.
Sanfoundry Global Education & Learning Series – Cytogenetics.
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