Cell production system

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Ribosomes[edit | edit source]

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[edit | edit source]

  • 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)[edit | edit source]

  • 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)[edit | edit source]

  • 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)[edit | edit source]

  • 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


Links[edit | edit source]

Literature used[edit | edit source]

  • JUNQUIERA, L. Carlos – CARNEIRO, José – KELLEY, Robert O.. Fundamentals of Histology. 1. edition. Jinočany : H & H 1997, 1997. 502 pp. ISBN 80-85787-37-7.