We
already know about the general characteristics of prokaryotes, now
let's proceed to the external structure of prokaryotes. There are 4
components outside of the cell wall; glycocalyx, flagella, axial
filaments and fimbrae & pili.
Glycocalyx
is the substance that surrounds the cell. If they are organized, it's
called capsule. If they are unorganized and loose, it's called slime
layer. They functioned as source of nutrients, protect the cell
against dehydration, attachment to various surfaces and protection
from phagocytosis.
Flagella
is the long appendages that propel the bacterial cell. Arrangements :
 |
| Flagella parts |
Axial filaments or endoflagella are bundles of fibrils that arise at the ends of the cell beneath the outer sheath and they are spiral around the cell. They also present in a spirochetes group of bacteria. Examples : Treponema pallidum & Borrelia burgdorferi.
Fimbrae and Pili are hair-like appendages that are shorter, straighter and thinner than flagella. They consist of a protein called pilin arranged helically around a central core. They are used for attachment rather than mobility.
Cell wall composed of a macromolecular network called peptidoglycan (also known as murein). Peptidoglycan consists of a repeating disaccharide. Disaccharide portion is made up of monosaccharides called N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM). Alternating NAM and NAG are linked in row by B-1,4 glycosidic bonds [sensitive to lysozymes]
