The Composition of Ribosomes
Prokaryotic ribosomes
-
Sedimentation coefficient: 70S
-
small subunit: 30S
-
One rRNA molecule (16S)
-
21 different proteins, designated S1-S21
-
large subunit: 50S
-
Two rRNA molecules (5S and 23S)
-
31 different proteins, designated L1-L31 (L12 is present
in four copies)
|
The sedimentation coefficient is measured in Svedberg
units (S): the rate of sedimentation of a component in a centrifuge
is related both to the molecular weight and the 3-D shape of the component.
|
The rRNA components of the prokaryotic ribosome
|
Type
|
Approximate number of nucleotides
|
Subunit location
|
|
16S
|
1,542
|
30S
|
|
5S
|
120
|
50S
|
|
23S
|
2,904
|
50S
|
RNA function and turnover in the cell
|
Type
|
Function
|
Different Kinds
|
Nucleotides
|
% of Synthesis
|
% of Total RNA
|
Stability
|
|
mRNA
|
Messenger
|
Thousands
|
500-6000
|
40-50
|
3
|
T1/2 = 1-3 min
|
|
rRNA
|
Ribosome
|
3 (23S, 16S, 5S)
|
2904, 1542, 120
|
50
|
90
|
Stable
|
|
tRNA
|
Adapter
|
~50
|
73-93
|
3
|
7
|
Stable
|
Separation of ribosomal proteins by 2D gel electrophoresis
(a) small (30S) subunit; (b) large (50S)
subunit
In 1968, Dr. M. Nomura, a professor here at UCI, was the first to show
that the 30S subunit could be reassembled from the individual components.
He found that the order of addition of components was critical.
Eukaryotic ribosomes
-
Sedimentation coefficient: 80S
-
small subunit: 40S
-
One rRNA molecule (18S)
-
33 different proteins, designated S1-S33
-
large subunit: 60S
-
Three rRNA molecules (5S, 5.8S, and 28S)
-
50 different proteins, designated L1-L50
The rRNA components of the eukaryotic ribosome
|
Type
|
Approximate number of nucleotides
|
Subunit location
|
|
18S
|
1,900
|
40S
|
|
5S
|
120
|
60S
|
|
5.8S
|
156
|
60S
|
|
28S
|
4,700
|
60S
|
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