Plasmids

Question 1

Describe plasmids.

Answer 1

Plasmids are double-stranded DNA molecules which can be linear or made of RNA (Willey, Sherwood, Woolverton, 2011, pp.71-73).
They may be integrated with the chromosome, but can exist and replicate independently of it (Willey, Sherwood, Woolverton, 2011, pp.71-73).

References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.

Question 2

Describe an episome.

Answer 2

An episome is a plasmid that is integrated with the chromosome (Willey, Sherwood, Woolverton, 2011, pp.71-73).

References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.

Question 3

Describe how plasmids differ from chromosomes.

Answer 3

Plasmids contain few genes, and the genes it contains are not essential for the host, although it gives the host selective advantages (Willey, Sherwood, Woolverton, 2011, pp.71-73).

References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.

Question 4

Describe conjugative plasmids.

Answer 4

Conjugative plasmids use conjugation to transfer their copies to other bacteria (Willey, Sherwood, Woolverton, 2011, pp.71-73).
They transfer their copies by forming a pilus.

References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.

Question 5

Describe F factor plasmids.

Answer 5

F factor stands for fertility factor.
These plasmids carry genes for conjugation.
For example, they contain tra genes which allow expression of sex pili.

Question 6

Describe R factor plasmids.

Answer 6

R factor stands for resistance factor and these plasmids give cells antibiotic resistance.

Question 7

Describe Col plasmid.

Answer 7

Col plasmids contain genes for colicin synthesis, which are bacteriocins (Willey, Sherwood, Woolverton, 2011, pp.71-73).
Bacteriocins are proteins which destroy closely-related bacteria (Willey, Sherwood, Woolverton, 2011, pp.71-73).

References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.

Question 8

Describe virulence plasmids.

Answer 8

Virulence plasmids make their hosts more pathogenic (Willey, Sherwood, Woolverton, 2011, pp.71-73).

Question 9

Describe metabolic plasmids.

Answer 9

Metabolic plasmids encode enzymes that degrade substances like pesticides, sugars and aromatic compounds (Willey, Sherwood, Woolverton, 2011, pp.71-73).

Question 10

Describe plasmid compatability.

Answer 10

To co-exist in a cell, the plasmids must be compatible.
Plasmids in the same family are incompatible and cannot co-exist in the same cell as they compete for the same replication or partitioning machinery.

Question 11

Describe the difference between mobilisable plasmids and non-mobilisable plasmids.

Answer 11

Mobilisable plasmids can be transferred via conjugation, while non-mobilisable plasmids can only be transferred via natural transduction or transformation.