Cell production system

Ribosomes
Ribosomes are small electron-dense particles measuring 20 x 30 nm.
 * composed of a small (40S) and a large (60S) subunit
 * from 4 types of rRNAs and about 80 different proteins
 * two classes of ribosomes:
 * 1) of prokaryotes, chloroplasts and mitochondrias, and
 * 2) of eukaryote
 * are formed in the nucleolus, their proteins are synthesized in the cytoplasm
 * strongly basophilic → react with basic dyes
 * occur either as individual granules or in clusters = polyribosomes (held together by mRNA)
 * proteins formed for the cell's own use are synthesized on unbound polyribosomes
 * the association of rRNA and ribosome occurs in the nucleus, complete ribosomal subunits travel out of the nucleus through nuclear pores

Endoplasmic reticulum

 * the site of synthesis of lipids and saccharides
 * segregation of proteins from the cytoplasm and initial posttranslational modification (preparation for specific functions) occurs here
 * in fully differentiated cells there are 2 types of endoplasmic reticulum:
 * 1) rough ER
 * 2) smooth ER

Rough endoplasmic reticulum (GER)

 * also granular; rought
 * in cells specialized for protein secretion (pancreatic, fibroblasts, plasma cells)
 * composed of' tubules' and parallel clustered flat cisternae formed by membranes sometimes associated with the outer envelope of the nucleus
 * the presence of ribosomes and polyribosomes on the cytoplasmic surface of the reticulum membrane, which give it a granular appearance
 * Ribosomes are responsible for the basophilic properties
 * the main task is the segregation of proteins for export or transfer to other cytoplasmic components
 * initial glycosylation of glycoproteins containing nitrogenous oligosaccharides, synthesis of phospholipids, post-translational modification of newly formed polypeptides
 * proteins synthesized in the GER have different destinations, may remain in the cytoplasm or be segregated from it and participate in different cellular activities

Smooth endoplasmic reticulum (HER)

 * also agranular; smooth
 * also forms the intracellular network
 * without associated ribosomes
 * cisternae are tubular; huge number of interconnected channels of various shapes and sizes
 * membranes of HER arise from rough ER → often merge into each other
 * synthesis of lipids, phospholipids, carbohydrates and steroid hormones
 * sarcoplasmic reticulum: a specialized form of the HER that is involved in the process of muscle cell contraction (reservoir of calciums)
 * often in steroid hormone synthesizing cells (ovary, testis, adrenal gland), and in hepatocytes (detoxification reaction)

Golgi complex (GK)

 * determines post-translational modification of products synthesized by the cell, envelops them and labels them with the destination address
 * of three distinct compartments bounded by a smooth membrane:
 * 1) mildly curved sheathed cisternae,
 * 2) a large number of small pouches and
 * 3) several larger vacuoles located at one pole of the GC
 * functional connection between the ER and the rest of the cell (difficult to determine its boundaries)
 * ER → newly formed protein → GK cisternae (the nearest cisterna is called the production = convex = cis region), in the trans region (concave = matric) vesicles gather → condensing vacuoles (these structures bud from Golgi cisternae and split off as vesicles transporting proteins to various sites)
 * plays an important role in glycosylation, sulfation, phosphorylation and selective proteolysis of proteins