Ribosome

Ribosome (plural ribosomes) is a component of cells whose primary function is to carry out translation, i.e., the creation of protein from mRNA (the second step in the central dogma of molecular biology).

Summary

Item	Value
Type of organisms whose cells contain ribosomes	all organisms. Ribosomes are crucial to the central dogma of molecular biology which is common to all forms of life. However, there are some qualitative and size differences between prokaryotic ribosomes and eukaryotic ribosomes.
Type of cells within the organism that contain ribosomes.	All cells
Number of ribosomes per cell	?
Size	About 20 nm ($1nm=10^{-3}\mu m=10^{-9}m$) for prokaryotic ribosomes and 25 - 30 mn for eukaryotic ribosomes
Location within cell	some are attached to the outside of the rough endoplasmic reticulum or to the nuclear envelope. The proteins made by these are transferred into the endoplasmic reticulum, modified, and packaged for export to specific organelles or to other cells. others, called free ribosomes or cytoplasmic ribomoes, are found freely floating in the cytoplasm.