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The cytoplasm of P. multimicronucleatum like all other cells
contains a large number of organelles that are membrane bound.
Membranes are used to compartmentalize and isolate metabolic and
enzymatic processes within a continuous cytosol and cytomatrix which
is the background phase of the cytoplasm. The principle site of
biogenesis for secretory proteins, lysosomal hydrolases and membrane
lipids and proteins is the endoplasmic reticulum (ER), a system of
membrane cisternae (er) and tubules. This quick-freeze
deep-etch preparation of a living cell shows an extensive fracture
through the ER showing its P-fracture face. Intramembrane particles
(IMPs) form clumps and patterns rather than being evenly spread within
the membrane. Some of these IMPs probably represent sites of ribosome
attachment to translocons. Translocons are intramembrane pores through
which proteins are translocated into the ER during their translation.
The flattened ER cisternae morph into tubular ER at the left.
m, mitochondrion. EM taken on 6/5/91 by R. Allen with Zeiss 10A
TEM. Neg. 19,800X. Bar = 0.2µm.
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