F plasmid

a type of plasmid

1. F PLASMID SUBMITTED BY, ATHIRA.B DEPT: OF MICROBIOLOGY SRM ARTS AND SCIENCE COLLEGE KATTANGULATHUR

2. INTRODUCTION A plasmid is a small,circular,extrachromosomal double stranded DNA that has the capacity to replicate independently. Discovered by Landerberg in1952 It naturally occur in bacteria, and also they have low copy number(1-4 per cell)or a high copy number(10-100 per cell). Sometimes present in archea and eukaryotes Genes carried in plasmid benefit the survival of the organism by providing them with genetic advantages like antibiotic resisitance etc.under certain situation or particular conditions They provide mechanism for horizontal gene transfer within a population of microbes and thus provide a selective advantage under a given environmental state.

3. TYPES OF PLAMID 1 . ON THE BASIS OF FUNCTION a. Fertility Plasmid (F-Plasmid) b. Resistance Plasmid(R- Plasmid) c. Col Plasmid d. Degradative Plasmid e. Virulence Plasmid 2. BY THEIR ABILITY TO TRANSFER TO OTHER BACTERIA a. Conjugative Plasmid b. Non-Conjugative Plasmids c. Intremediate classes of plasmids

4. F- PLASMID F- Plasmid or fertility factor is a conjugative plasmid of Escherichia coli First plasmid discovered and has been significant in the development and practice of bacterial genetics Like other plasmids, F plasmid have a circular structure and measure about 100kb F Plasmid plays an important role in reproduction given that they contain genes that code for the production of sex pilus as well as enzymes required for conjugation. F plasmid also contains genes that are involved in their own transfer, therefore during conjugation they enhance their own transfer from one cell to another. E.coli containing this F factor are known as F+ and those without are known as F- .

5. STRUCTURE OF F-PLASMID F factor is 100 kb of duplex DNA with two replication-origin regions. a. The ori v or vegetative replication – contains 2 replication origins, one of which is used for bi directional replication of plasmid when it is not being transferred to another cell. b. The ori T , the transfer origin – promotes a special mode of unidirectional, single strand replication used during conjugative transfer of F factor to another cell. Some of the main parts of F plasmid include:- - Transposable element( IS2,IS3 and Tn1000) - facilitates interaction between F factor and other DNA molecules. - Replication sites( RepFIA , RepFIB , RepFIC ) - Origin of conjugative transfer( oriT ) - Replication origin regions - Tra operon – encodes functions required for conjugative transfer of the F factor .

6. REPLICATION OF F- PLAMID Replication of F plasmid is ROLLING CIRCLE REPLICATION(RCR) RCR is a mechanism adopted by certain plasmids,among other genetic elements, that represents one of the simplest initiation strategies :- - nicking by a replication initiator protein on one parental strand to generate the primer for leading strand initiation and a single priming site for lagging strand synthesis All RCR plasmid genomes consists of a number of basic elements : leading strand initiation and control, lagging strand origin. RCR has been mainly characterized in Gram – positive bacterial plasmids, although it has also been described in Gram-negative bacterial or archeal plasmids.

7. In F plasmid replication 1. relaxosome nicks DNA 2. extend at 3’-OH 3. displace parent strand 4.synthesize complement for displaced strand.

8. TRANSFER OF F PLASMID F plasmid transfer through conjugation method,which occurs due to the pilus known as F pilus. All the proteins that are associated with the F pilus are transcribed and translated from genes within the F factor The F plasmid is not transferred to a F- cell via the F pilus, the F pilus merely pulls the two cells together allowing a conjugative junction to form,which contain a pore that allows the DNA to pass from the F+ cell to the F- cell. During the transfer, the F plasmid unwinds and the outer strand breaks, which will be the one that is transferred to the F- cell via the pore in the conjugative junction. Replication of the plasmid then takes place in order to make both single strands to DNA into double stranded DNA plasmids. In the original F+ cell, the single strand merely undergoes rolling circle replication to once again become double stranded. In the recipient cell, the linear single-stranded DNA is replicated into a double strand and becomes a circular F plasmid containing the F factor.

9. Both E.coli cells are now considered to be F+ cells and therefore can both now transfer the plasmid and therefore can both now transfer the plasmid and therefore the F factor.

10. THANK YOU