Page 30 - Veterinary Histology of Domestic Mammals and Birds, 5th Edition

12 Veterinary Histology of Domestic Mammals and Birds

through complex protein channels into the lumen of the
VetBooks.ir ER, where they undergo modification including:

· folding,
· formation of disulfide bonds and
· initial glycosylation.

A degree of quality control also occurs in the rER, with
incorrectly folded proteins being exported to the cytosol
where they are degraded by proteases.
Glycosylation primarily takes place on the inner, luminal
surface of the ER membrane, and is subsequently completed
by the Golgi apparatus. Transport vesicles budding from
the ER membrane pass to the Golgi apparatus, endosomes,
lysosomes, peroxisomes, the plasmalemma and the nuclear
membrane. Most of the proteins contained in these vesicles
are glycosylated with oligosaccharide chains.
The proteins carried by the transport vesicles contribute
to metabolism within the aforementioned organelles or are
1.15 Smooth endoplasmic reticulum (sER) (x16,000). released from the cell as secretory product. They are also incor-
porated into cellular membranes. The rER thus assumes an
Function: The rough endoplasmic reticulum plays important role in intracellular transport and communication.
a central role in intracellular metabolism. It synthesises Rough endoplasmic reticulum is particularly prominent
cell-specific molecules from substances that have been in protein-secreting gland cells. Dense accumulations of
endocytosed and broken down by the lysosomal enzyme ER-cisternae are present in the basal cytoplasm. Under the
system. Products of cytoplasmic metabolism make a sig- light microscope this portion of the cytoplasm appears as a
nificant contribution to this synthetic process, providing a basophilic region referred to as ergastoplasm.
range of ‘building blocks’ for new cellular products. At the
ER membrane, these substrates are assembled into mac- SMOOTH ENDOPLASMIC RETICULUM (RETICULUM
romolecules that are required by other cellular organelles ENDOPLASMATICUM NONGRANULOSUM)
to perform their specific functions. The smooth endoplasmic reticulum consists of predomi-
Ribosomes are integral in the synthesis of proteins nantly short, interconnected tubules that do not have
by the rER. Newly synthesised ribosomal proteins pass ribosomes on their surface (Figures 1.6 and 1.15).

1.16 Golgi apparatus with central centriole pair and adjacent smooth and rough endoplasmic reticulum
(schematic).

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