STRUKTUR DAN FUNGSI SEL MIKROBA

Pokok Bahasan Mata Kuliah Mikrobiologi Dasar Program Studi Biologi (S1) Fak. Biologi UNSOED

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

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