Microbiology Demystified

• Gram-negative.Agram-negative cell wall (Fig. 4-4) is thin. The inside is
  made of peptidoglycan. The outer membrane is composed of phospholipids
  and lipopolysaccharides.

The cell wall does not retain the crystal of violet dye when the cell is stained.
The cell appears pink when viewed with a microscope.

CYTOPLASMIC MEMBRANE

The prokaryotic cell has a cell membrane called the cytoplasmic membranethat
forms the outer structure of the cell and separates the cell’s internal structure
from the environment. The cytoplasmic membrane is a membrane that provides
a selective barrier between the environment and the cell’s internal structures.
The cytoplasmic membrane (Fig. 4-5) provides a selective barrier, allowing
certain substances and chemicals to move into and out of the cell. The cyto-
plasmic membrane is a bilayer of phospholipids that has polar and nonpolar
parts, which is referred to as being amphipathic. The nonpolar parts share elec-
trons of atoms equally. The polar parts share electrons unequally. Each polar
part has a head that contains phosphate and is hydrophilic (“water-loving”).
Each nonpolar part has two tails composed of long fatty acids that are hydro-
phobic (“water-fearing”).

CHAPTER 4 Prokaryotic and Eukaryotic Cells^73

Phospholipid

Integral protein

Lipopolysaccharide

Peptidoglycan

O-specific

side chains

Porin

Braun’s

lipoprotein

Outer

membrane

Periplasmic

space and

peptidoglycan

Plasma

membrane

Fig. 4-4. Gram-negative cell wall.