Page 97 - Academic Press Encyclopedia of Physical Science and Technology 3rd Molecular Biology

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Encyclopedia of Physical Science and Technology EN017F-788 August 3, 2001 16:27

38 Translation of RNA to Protein

TABLE I Properties of Ribosomes and Ribosomal Subunits
RNA:protein rRNA S 20,w
Source S 20,w Size (nm) a Mass (Mda) (w/w) Axial ratio mass (Mda) (nominal)
Ribosomes
Prokaryotes
E coli 70 22.5 ± 2.5 2.6–2.9 2:1 — f
Eukaryotes
Cytoplasm 80 28.0 ± 2.8 3.4–4.5 1:1 —
Chloroplast 70 22.5 ± 2.5 2.5–3.3 1:1 —
Mitochondria b
Protists c 60–80 ca. 3.25 1:1.38 —
Animals 55–60 2.7–3.2 1:1.7–1:4 —
Fungi 67–80 4.2 1:1.3–1:1.6 —
Higher plants 78 — — —
Small ribosomal subunits
Prokaryotes
E. coli 30 22.0 ± 2.2 0.95 2:1 2:1 0.6 16
Eukaryotes
Cytoplasm 36–41 25.0 ± 2.5 1.4 1:1 2:1 0.7 18
Chloroplast 28–35 22.0 ± 2.2 1.2 1:1 2:1 0.6 16
Mitochondria
Protists 32–45 — — — 0.2–0.35 11–16
Animals 32–40 1.1–1.6 — — 0.31 12–14
Fungi 32–29 1.6–1.7 — — 0.45–0.64 15–19
Higher plants 44 — — — 0.64 18
Large ribosomal subunits
Prokaryotes
E. coli 50 22.5 ± 2.2 1.75 2:1 1:1 1.17 23
0.04 5
Eukaryotes
Cytoplasm 60 28.0 ± 2.8 2.1–3.1 1:1 1:1 1.2–1.75 25–28
0.05 5.8
0.4 5
Chloroplasts 46–54 22.5 ± 2.2 2.4 1:1 1:1 1.1 23
0.04 5
0.03 d 4.55 d
Mitochondria
Protists 45–60 — — — 0.4–0.74 12–24
Animals 25–35 1.65–2.0 — — 0.5 16–21
Fungi 50 — — — 0.77–1.22 21–25
Higher plants 60 — — — 1.25 26
0.04 e 5 e
a Largest dimension.
b Mitochondrial ribosomes are preferentially associated with the inner mitochondrial membrane and are more diverse than

cytoplasmic or chloroplast ribosomes. Particular features include post-transcriptional oligoadenylation of the 3 ends of both the
smaller and larger rRNA components. Except for mitochondrial ribosomes of higher plants, the essential sequence motifs 5S
rRNA and 5.8S rRNA are present in the large rRNA component and are not found as individual species.
c
Mitochondria of protists such as Trypanosoma brucei are also known as kinetoplasts.
d
4.5S rRNA corresponding to the 100 nucleotides at the 3 end of the 23S rRNA in eubacteria occurs as a separate species in
chloroplasts of higher plants.
e
This species is present only in plant mitochondria and is absent from all other mitochondrial ribosomes.
f
Data not available.