Estructura y composición de la célula procariótica. (célula sin núcleo y…
- Estructura y composición de la célula procariótica.
The structure of the lipid phase provides an
impenetrable barrier to many substances. This property accounts
for the selective permeability and capacity to regulate transport
of molecules. Bacterial cell membranes contain primarily phospholipids
(making up about 30%–40% of the membrane mass)
and proteins (contributing 60%–70%). Major exceptions to this
description are the membranes of mycoplasmas, which contain
high amounts of sterols—rigid lipids that stabilize and reinforce
the membrane—and the membranes of archaea, which contain
unique branched hydrocarbons rather than fatty acids.
Although bacteria lack complex internal membranous organelles,
some members develop stacked layers of internal membranes
that carry out physiological processes related to energy and synthesis.
These membranes are usually an outgrowth of the cell
membrane extending into the cytoplasm, which can increase the
membrane surface area available for these reactions. Examples of
cells with internal membranes are cyanobacteria, whose thylakoid
membranes are the sites of photosynthesis