A typical prokaryotic cell represents by the bacteria and the different bacterial cell structures presents in bacterial cell are as follow:
[A] Cellular projection
i) Flagella
ii) Pili
iii) Fimbrae
[B] Protective layers
i) Capsule
ii) Cell Wall
iii) Cell Membrane
[C] Cytoplasm
i) Cytoplasm
ii) Nucleoid
iii) Cytoplasmic Organelles
Now we shall go for details: -
[A] Cellular projection
a) Flagella: - the flagella may present in two different processes, i.e. either close to the poles or distributed along the whole cell. In the bacterial cell structure the flagella arise from the cytoplasm and emerge from the cell with a tubular whip-like projection.
[b]Structure of flagella:
The flagella are divided into three parts, those are the basal body, hook like structure and terminal filament.
i) The Basal Body: It remains within the cytoplasm and consist of upto four rings arranged in a linear sequence in Gram negative bacteria. They are the M ring and S ring corresponding to the cell membrane and also P and L ring, corresponding to the peptidoglycan and the outer membrane. But in the case of Gram positive bacteria the outer two rings are not present.
Attachment of Flagella
ii) Hook like portion: It is the intermediate part connecting the terminal filament with the basal body also named as axoneme.
iii) The main filament: it remains at the terminal part of the flagella.
[c] Type of flagella:
The flagella may be classified on the basis of their position from where it arises in the bacterial cell structure, such as atrichous( no flagella), monotrichous, lophotrichous, amphrichous and peritrichous.
[d] Chemical Composition:
The flagella having a single microfilament, which are formed of protein sub-unit and it is named as flagellin.
[e] Functions of Flagella:
It helps in bacterial motility for procuring food. It also helps in the reproduction of bacteria.
[B] Pili:
[a] Structure of Pili:
Those are the short filamentous appendages of bacterial cell structure in some gram negative bacteria like Shigella.They are smaller than flagella and some are long and thin, on the other hand some are short and rigid. They consisting of an helical protein called Pii.
[b] Functions of Pili:
The Pili form a bridge at the time of bacterial conjugation and also provide the passage of exchange of genetic material during conjugation.
[C] Fimbrae:
[a] Structure of Fimbrae:
In the primary stage Fimbrae were believed to be the same as Pili, though they are variable in size and is formed of a non polar protein in some germ negative bacteria, such as Neisseria. They are different from Pili in terms of their functions also.
[b] Functions of Fimbrae:
During infection it has the attachment to the host’s cell. They also act as an organ for binding the cells together.
In the study of Bacterial cell structure we shall have now some discussion about protective layer of bacterial cell and the cytoplasm of bacterial cell in the following chapter.