Plasma Membrane

Bacterial plasma membrane is a unit membrane, which contains both protein and lipid. The amount of protein and lipid varies widely and generally bacterial plasma membrane contains more amount of protein as compare to eukaryotic membranes. One major difference between the eukaryotic and prokaryotic plasma membrane is that prokaryotic membranes lack sterols such as cholesterol. On the contrary, bacterial cells contain pentacyclic sterol like molecules known as hopanoids. Hopanoids are synthesized from the same steroids precursor and they play the role similar to that of sterol in eukaryotic cells.

Functions: Plasma membrane acts as a transport system for nutrient uptake, protein secretion and waste excretion. It basically acts as a selectively permeable barrier thereby allowing only particular molecules and ions to pass in and out of the cell and restricting the movement of others. Plasma membrane is also a site for a number of metabolic processes like photosynthesis, respiration, synthesis of lipids etc. It also contains some receptor molecules that help in detecting and responding to the surrounding chemicals. Presence of invagination in plasma membrane helps in chromosome replication or cross wall formation in dividing bacteria. This invagination may be in the shape of tubules, vesicles or lamellae. Lamellae shaped invagination are known as mesosome, which are present in both Gram positive and Gram negative bacteria but are more prominent in Gram positive one. 

Note: Plasma membrane of all the bacteria lacks sterol except Mycoplasma.