Membran Sel Prokariotik

The plasma membrane
1	The plasma membrane of bacteria consists of a phospholipid bilayer with hydrophilic surfaces (interact with water) and a hydrophobic interior (insoluble in water); such asymmetric molecules are said to be amphipathic; most bacterial membranes lack sterols
2	Many archaeal membranes have a monolayer instead of a bilayer; archaeal membranes are describe in more detail in chapter 20
3	The fluid mosaic model is the most widely accepted model of membrane structure. It distinguishes two types of proteins associated with the membrane: peripheral (loosely associated and easily removed) and integral (embedded within the membrane and not easily removed)
4	The membrane is highly organized, asymmetric, flexible, and dynamic
5	The plasma membrane serves several functions
	a	It retains the cytoplasm and separates the cell from its environment
	b	It serves as a selectively permeable barrier, allowing some molecules to pass into or out of the cell while preventing passage of other molecules
	c	It is the location of a variety of crucial metabolic processes including respiration, photosynthesis, lipid synthesis, and cell wall synthesis
	d	It may contain special receptor molecules that enable detection of and response to chemicals in the surrounding
Internal membrane systems
1	Mesosomes are structures formed by invaginations of the plasma membrane that may play a role in cell wall formation during cell division and in chromosome replication and distribution; however, mesosomes may be artifacts generated during chemical fixation for electron microscopy
2	Photosynthetic bacteria may have complex infoldings of the plasma membrane that increase the surface area available for photosynthesis
3	Bacteria with high respiratory activity may also have extensive infoldings that provide a large surface area for greater metabolic activity
4	These internal membranes may be aggregates of spherical vesicles, flattened vesicles, or tubular membranes