Gram Positive Bacterial Cell Wall

Picture of Gram +ve bacterial cell wall. The image above is 400 pixels across and the original is 2,000 pixels across.

The Gram positive cell wall has a thick peptidoglycan (orange red in this picture) layer outside the plasma membrane. There may be a gap or periplasmic space between the peptidoglycan layer and the plasma membrane. Various membrane proteins can be seen floating in the plasma membrane. Elongate molecules called teichoic acids intermesh with the peptidoglycan layer. Some of the teichoic acid molecules have a lipid portion (and are called lipoteichoic acids) which binds the molecules to the underlying plasma membrane. In this diagram, the outer aspect of the wall is covered in a regular arrangment of proteins called an S-layer. A good example of an S-layer is shown in our diagram of anthrax.

GRAM STAIN
Gram positive cells retain the Gram stain, probably because the thick peptidoglycan layer prevents the stain from being leached out by alcohol in the staining process.

PEPTIDOGLYCAN
Peptidoglycan forms a huge polymer that envelopes the entire cell. This sheath can often be isolated and viewed with an electron microscope. The molecules consist of strings of sugar molecules. These strings are linked together by chains of amino acids into a huge network.

PERIPLASMIC SPACE
This apparent gap between the peptidoglycan layer and the plasma membrane mighht be a less dense gel of peptidoglycan. The region might host various molecules such as enzymes.

PLASMA MEMBRANE
The plasma membrane is a phospholipid bilayer, similar to that found in eukaryotic cells.