and is a major component of hyperthermophilic archaea. this molecule spans the whole thickness of their cytoplasmic membrane as in some other bacteria, discussed previously. cyclopentanes are found in the hydophobic tails of hyperthermophilic archaeal membranees. in addition to glycerol, tetritol and nonitol constitute methanogenic archaeal phospholipid. unlike bacteria, the hydrophilic head groups in archaea are oligosaccharides or sulfonated oligosaccharides in addition to phosphate compounds.
in bacteria and eukaryotes,membrane fluidity is determined by the degree of saturation of the phospholipid fatty acid according to the temperature at which they grow. little is known about how membrane fluidity is controlled in archaea, which can have optimum temperatures that span from ambient to over 100
2.3.3.4 protein
in addition to an isolation function, the cytoplasmic membrane has many physiologically important function carried out by the proteins which constitute 50-60 of the membrane. Membrane proteins are divided into two classes according to their location: integral and peripheral proteins. The surface of the integral proteins is hydrophobic and they are embedded in the membrane through hydrophobic interaction with the hydrophobic tails of the phospholipids. They can be removed from the membrane with detergents. Peripheral proteins can be removed by washing using salt solutions since they are attached to the membrane by ionic interactions.
Many of membrane proteins mediate solute transport and protein secretion. Water molecules are diffusible through the lipid bilater but the diffusion rate is too low to explain the rapid water flux that occurs to counter osmotic shock. A water channel known as aquaporin has been identified in the cytoplasmic membrane of many organisms including bacteria. The aquaporin gene(aqpZ) in E.coli is growth phase and osmotically regulated. aqpZ has a role in both short – and long-tern osmoregulatory responses, and is required for rapid cell growth. Aquaporin is known to be necessary for expression of virulence in pathogenic bacteria, and for sporulation and permination.
Enzymes responsible for synthesis and turnover of surface structure, such as phospholipase, protease and peptidase, are also associated with the cytoplasmic membrane. The bacterial chromosome is attached to the membrane, and also some of the enzymes involved in DNA replication. Bacterial DNA is attached to the cytoplasmic membrane via a protein that is believed to be responsible for chromosome segregation into daughter cells during cell division.
The ATP synthase (ATPase) enzyme complex is a membrane protein that couples ATP synthesis and hydrolysis to transmembrane proton transfer, thereby governing the proton motive force, p, and the energy status of the cell.
The cytoplasmic membrane is the site of oxidative phosphorylation. Proteins of the electron transport system are arranged in the cytoplasmic membrane in such a way that protons are expelled into the periplasmic region with the free energy available from the electron transport process. Photosynthesis proteins are localized in the cytoplasmic membrane of photosynthetic bacteria. Rhodopsins are found in halophilic archaeal membrane when grow under oxygen-limited conditions. They are responsible for phototaxis and for proton export utilizing light energy.
Prokaryotes employ two-component systems to regulate metabolism in response to environment change. The sensor proteins of such two-component systems are localized within the cytoplasmic membrane.