List of abbreviations
of micros-
specialist terms
explained in
English +

Every attempt was made to provide correct information and labelling, however any liability for eventual errors or incompleteness is rejected!

dieser Seite

Dr. med.
H. Jastrow

of use
Overview Ribosome (Ribosoma):
Pages with explanations are linked to the text below the images when available
(Detail, rat)
Stereo image of ribosomes of
the Nissel substance (rat)
Nissl substance
+ polyribosomes (guinea-pig)
Ribosomes on RER
of a human plasma cell
free and RER-bound ribosomes
(plasma cell rat)
human plasma cell RER + free
ribosomes, pharyngeal tonsil
human plasma cell 2 
pharyngeal tonsil
detail 1:
detail 2: free + RER-
attached ribosomes
detail 3:free + RER-
attached ribosomes
human plasma cell
with RER
human plasma cell: RER
and free ribosomes
ribosomes, RER and
lipofuszin-vesicle (human)
RER of a human
plasma celll
RER + primary Lysosomes
human plasma cell
Ribosomes (Terminologia histologica: Ribosomae) are very tiny cell organelles consisting of ribosomal RNA and globular proteins. They have diameters of 10 - 25 nm, and they are present in all living cells.
Several milions of these spherical corpuscules that are not surrounded by membranes are encountered in cells with high output of proteins. A basophilic staining in light microscopy points to a high content of ribosomes since their rRNAs bind to basic staining chemicals.
Ribosomes are seen singly but more often lie in groups along messenger RNAs. These groups are called Polyribosomes, Polysomes or Ergosomes. Further a great amount of ribosomes is embedded in the outer membrane of the rough endoplasmic reticulum (RER) and the outer nuclear membrane which is connected to the RER.
Ribosomes are assembled in the nucleoli. In humans and mammals they possess a greater 60s and a smaller 40s subunit. Both of them are combined to the 80s ribosom (s = band in which particles are seen after ultracentrifugation). The 60s subunit is comprised of 50 different proteins, a "free" 5s rRNA (ribosomal ribonucleic acid) with 120 bases, a 160 base-long 5,8s rRNA, which is bound on a third 28s rRNA with 4,800 bases. The 40s subunit has 33 different proteins and a 1,900 base-long 18s rRNAt.
Ribosomes serve for protein synthesis involving a process called translation.Translation is the realisation of the genetic information. The aminoacid sequence of the synthesised protein corresponds to the copy of the genetic code present in the m-RNA attached to the ribosome. Proteinbiosynthesis is present during the G1-phase of the cell cyclus, the phase of proliferation that belongs to mitotic interphase.
There are three steps in protein synthesis:
1. Initiation: a m-RNA binds to the 40s-subunit of a ribosome.
2. Elongation: tranfer-Ribonucleic acids (t-RNAs) bind to the ribosome according to the copy of the genetic code on the m-RNA beginning at the startcodon. The specific bound aminoacids of the t-RNAs are linke to each other by means of the enzyme peptidyl-transferase to form the coded protein. After delivery of its aminoacid a t-RNAs leaves the ribosome to give space for the next one while the protein is elongating.
3. Termination end of the process: when the stopcodon of the m-RNA is reached the ribosome dissolves into its subunits and the protein splices from the last t-RNA.
Since many ribosomes are seen along one m-RNA many molecules of the same protein are synchronously syntetised.

--> rough endoplasmic reticulum (RER), outer nuclear membrane, nucleoli
--> Electron microscopic atlas Overview
--> Homepage of the workshop

Two pictures were kindly provided by Prof. Dr. H. Wartenberg. Page & copyright H. Jastrow.