Introductory Microbiology

Different parts of attachment of a flagellum in Gram-negative bacterium

Movement
The rings found in the basal body are probably involved. It is known that the flagellor motor is driven by the proton motive force (pmf) i.e the force derived from the electrical potential in the H+ ion gradient across the cytoplasmic membrane. Recent studies suggests that the concentration of cGMP (guanosine 3', 5' cyclic phosphoric acid) within the cell governs the direction in which the rotation occurs.
Prokaryotic cell is characterized by the absence of the endoplasmic reticulum(ER) and the cytoplasm membrane is the only unit membrane of the cell. However, the membrane may be some times infolded deep into the cytoplasm. Electron microscopy of most prokaryotes reveals only two internal regions, the cytoplasm and the nucleoplasm. The cytoplasm is granular in appearance and contains ribosomes that are smaller in size as compared to eukaryotic ribosomes. The nucleoplasm is fibrillar and contains DNA. Except, in mycoplasmas, other prokaryotes contain a defined rigid cell wall. No membranous structures similar to the mitochondria or chloroplasts are seen in the prokaryotes. Cytoplasm membrane is the site of respiratory electron transport in prokaryotes. In photosynthetic bacteria, the photosynthetic apparatus is located in a series of membranous, flattened structures similar to the thylakoids and these structures are not organised into chloroplasts but are dispersed in the cytoplasm. The cytoplasmic membrane contains specific sites for DNA attachment and also has a major role in cell division. The cell membrane, unlike in the eukaryotic cell does not generally contain sterols and poly unsaturated fatty-acids.
The genetic material located in the nucleolus which lacks a defined nuclear membrane. It consists of double helical DNA without any associated basic proteins and also contains extra chromosomal DNA, which can replicate autonomously, called as plasmids. Most prokaryotes possess a cell wall which is different in composition from that of eukaryotes and invariably contains a rigid polymer known as the peptidoglycan. Some prokaryotes possess this rigid structure show active movement with the aid of flagella. Some prokaryotes also show a gliding motility as in the blue green bacteria.
Sl No	Cellular organisation	Eukaryotes	Prokarotes
1	Nuclear membrane	+	-
2	Chromosome	>1	1
3	Nucleus	+	-
4	Histones	+	-
5	Golgi	+	-
6	ER	+	-
7	Mitochondria	+	-
8	Chloroplastids	+	-
9	Lysosomes	+/-	-
10	Cytoplasmic ribosomes	80s	70s
11	Organellular ribosomes	70 s	-
12	Presence of peptidoglycan in cell wall	-	+ or -
Table: Major differences in Eukaryotic and prokaryotic cellular organization.
Bacteria can be broadly divided into two major groups based on their gram staining characteristics such as Gram-positive and Gram-negative. The gram staining technique, the most widely used differential staining technique employed in bacteriology was first developed by Christian gram in the 19th century and is used primarily to divide bacteria into two broad groups.
Table:The general features of the gm +ve and gm-ve bacteria are as follows .

Gram + ve	Gram –ve
1) Capsules	1) Capsules
2) Peptidoglycan	2) Fimbriae
3) Cytoplasm	3) Cytoplasm
4) Flagellum	4) Flagellum
5)Mesosome and cytoplasmic membrane	5) Peptidoglycan
6) Genetic material	6) Genetic material
7) Plasmids	7) Outer membrane
8) Ribosomes	8)Mesosomes & cytoplasmic membrane
	9) Plasmids
	10) Ribosomes

• Most bacteria have atleast two structures around the cytoplasm namely cell wall (envelope) and the cytoplasmic membrane. Some may have additional components such as the outer membrane as in the gm –ve bacteria, a capsule and slime.
• Some bacteria which are motile have surface appendages with the aid of which they can move. In addition some others such as the gm -ve bacteria have short hair like structures called pilli(fimbriae) these are not essential for the growth and survival of the bacterial cells.

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