Molecular machine · RNA + protein
Ribosomes
The protein makers
In view
The mRNA ratchets through the gap between the subunits as tRNAs deliver amino acids, and the new protein chain snakes out of the exit tunnel. Neighbours on the same mRNA form a polysome.
A ribosome reads messenger RNA three letters (one codon) at a time and links the matching amino acids into a protein chain. Its small subunit does the reading and its large subunit does the joining. Together they are built from 4 RNA molecules and about 80 proteins.
Free ribosomes make proteins for the cytosol. Those docked on the rough ER make proteins for membranes and for export.
- Size
- 25–30 nm
- Mass
- 4.3 MDa
- Per cell
- ≈ 10 million
- Speed
- ≈ 5–6 amino acids/s
Did you know?
The ribosome is a ribozyme: RNA, not protein, catalyses the bond between amino acids. No protein atom sits within ~18 Å of the reaction, a discovery honoured with the 2009 Nobel Prize in Chemistry.
Sources
- 15.5 Ribosomes and Protein Synthesis · OpenStax · Biology 2e
- Targeting the Human 80S Ribosome in Cancer: From Structure to Function and Drug Design for Innovative Adjuvant Therapeutic Strategies · Gilles et al. 2020 · Cells
- The Endoplasmic Reticulum · Cooper 2000 · The Cell: A Molecular Approach, 2nd ed.
- 4.4 The Endomembrane System and Proteins · OpenStax · Biology 2e
- The endoplasmic reticulum: structure, function and response to cellular signaling · Schwarz & Blower 2016 · Cell Mol Life Sci
- Dimensions of ribosome · BioNumbers · BNID 111542
- Purification, characterization and crystallization of the human 80S ribosome · Khatter et al. 2014 · Nucleic Acids Res
- Number of ribosomes in HeLa cells · BioNumbers · BNID 107347
- Ribosome profiling of mouse embryonic stem cells reveals the complexity and dynamics of mammalian proteomes · Ingolia et al. 2011 · Cell
- The Structural Basis of Ribosome Activity in Peptide Bond Synthesis · Nissen et al. 2000 · Science
- The Nobel Prize in Chemistry 2009 · NobelPrize.org