PARTS OF PROKARYOTIC CELLS
Glycocalyx
Glycocalyx is a sticky, sugary envelope composed of polysaccharides and/or
polypeptides that surround the cell. Glycocalyx is found in one of two states. It can
be firmly attached to the cell’s surface, called capsule, or loosely attached, called
slime layer. A slime layer is water-soluble and is used by the prokaryotic cell to
adhere to surfaces external to the cell.
Glycocalyx is used by a prokaryotic cell to protect it against attack from the
body’s immune system. This is the case with Streptococcus mutans, which is a
bacterium that colonizes teeth and excretes acid that causes tooth decay. Normally
the body’s immune system would surround the bacterium and eventually kill it,
but that doesn’t happen with Streptococcus mutans. It has a glycocalyx capsule
state, which prevents the Streptococcus mutansfrom being recognized as a foreign
microorganism by the body’s immune system. This results in cavities.Flagella
Flagella (Fig. 4-2) are made of protein and appear “whip-like.” They are used by
the prokaryotic cell for mobility. Flagella propel the microorganism away from(^70) CHAPTER 4 Prokaryotic and Eukaryotic Cells
Capsule Ribosomes
Cell wall
Plasma
membrane
Chromosome
(DNA)
Nucleoid
Inclusion
body Flagellum
Fimbriae
S-layer
Fig. 4-1. A prokaryotic cell.