Overview of the structure and components of ribosomes

Ribosomes are the centers of protein synthesis.
They provide the workplace and the tools. The
70 S ribosome in prokaryotes consists of two
subunits of 30 S and 50 S. The 50 S subunit consists
of a large (23 S) and a small (5 S) rRNA of
~2900 and 120 nucleotides, respectively, and
33–35 different proteins; the 30 S subunit contains
a large 16 S rRNA and 21 proteins. The 50 S
subunit provides peptidyltransferase activity,
while the 30 S subunit is the site where genetic
information is decoded. The 30 S subunit also
has a proofreading mechanism to minimize errors
in translation. The whole ribosome has a
molecular weight of 2.5 million daltons (MDa)
and a sedimentation coefficient of 70 S. The
eukaryotic ribosome is much larger (4.2 MDa
and 80 S), with 60 S and 40 S subunits, which
contain an array of rRNAs and proteins as
shown in the figure. Recent observations of
bacterial 30 S and 50 S ribosomal subunit structures
at 5 Å resolution have helped to elucidate
the details of ribosomal structure and function.