F plasmid is a conjugative plasmid found in Escherichia coli that was the first plasmid discovered. It plays an important role in bacterial reproduction by containing genes that code for the production of sex pili and enzymes required for conjugation. The F plasmid replicates through a rolling circle mechanism and transfers between bacteria via conjugation using an F pilus. During conjugation, the F plasmid unwinds and one strand is transferred to the recipient cell where it is replicated to form a double-stranded circular plasmid, converting the recipient into an F+ cell capable of plasmid transfer.

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