Like all cells, a bacterium has a cell surface membrane (plasma membrane). It lies just inside the cell wall and surrounds the cytoplasm.Structure
The bacterial membrane has the same basic fluid mosaic structure as eukaryotic membranes: a phospholipid bilayer containing intrinsic and extrinsic proteins. A difference is that bacterial membranes usually contain no cholesterol.Functions
• Controlling entry and exit: the membrane is partially permeable. Channel and carrier proteins control the movement of ions, sugars, amino acids and waste products by diffusion, facilitated diffusion and active transport. The cell wall, by contrast, is freely permeable.
• Respiration: bacteria have no mitochondria, so the enzymes and electron carriers of aerobic respiration, and ATP synthase, are found on the cell surface membrane. It does the job of the inner mitochondrial membrane in eukaryotic cells.
• Photosynthesis: in photosynthetic bacteria such as cyanobacteria, the pigments are held on infoldings of the membrane or on internal membranes, because there are no chloroplasts.
• Anchoring structures: the motors of flagella are embedded in the membrane, and the DNA is attached to it during replication.
• Receptors in the membrane detect chemicals, allowing bacteria to move towards nutrients.So the prokaryotic membrane takes on roles that in eukaryotic cells are shared out between several organelles. For example, a drug that damages the bacterial membrane will stop both transport and ATP production.
The bacterial membrane has the same basic fluid mosaic structure as eukaryotic membranes: a phospholipid bilayer containing intrinsic and extrinsic proteins. A difference is that bacterial membranes usually contain no cholesterol.Functions
• Controlling entry and exit: the membrane is partially permeable. Channel and carrier proteins control the movement of ions, sugars, amino acids and waste products by diffusion, facilitated diffusion and active transport. The cell wall, by contrast, is freely permeable.
• Respiration: bacteria have no mitochondria, so the enzymes and electron carriers of aerobic respiration, and ATP synthase, are found on the cell surface membrane. It does the job of the inner mitochondrial membrane in eukaryotic cells.
• Photosynthesis: in photosynthetic bacteria such as cyanobacteria, the pigments are held on infoldings of the membrane or on internal membranes, because there are no chloroplasts.
• Anchoring structures: the motors of flagella are embedded in the membrane, and the DNA is attached to it during replication.
• Receptors in the membrane detect chemicals, allowing bacteria to move towards nutrients.So the prokaryotic membrane takes on roles that in eukaryotic cells are shared out between several organelles. For example, a drug that damages the bacterial membrane will stop both transport and ATP production.