Brent Cornell

    
Ribosomes

• Ribosomes are made of protein (for stability) and ribosomal RNA (for catalytic activity)
• They consist of a large and small subunit:
  • The small subunit contains an mRNA binding site
  • The large subunit contains three tRNA binding sites – an aminoacyl (A) site, a peptidyl (P) site and an exit (E) site
• Ribosomes can be found either freely floating in the cytosol or bound to the rough ER (in eukaryotes)
• Ribosomes differ in size in prokaryotes and eukaryotes (prokaryotes = 70S ; eukaryotes = 80S)

Structure of a Ribosome

Transfer RNA (tRNA)

tRNA molecules fold into a cloverleaf structure with four key regions:

• The acceptor stem (3’-CCA) carries an amino acid
• The anticodon associates with the mRNA codon (via complementary base pairing)
• The T arm associates with the ribosome (via the E, P and A binding sites)
• The D arm associates with the tRNA activating enzyme (responsible for adding the amino acid to the acceptor stem)

Structure of tRNA

Molecular Visualisation

To view the structure of a ribosome or a tRNA molecule via an interactive pop-up, click on the name of the structure below:

* Hint: For the ribosome, select nucleic acids and then colour structure by chain to identify the two subunits and three tRNA binding sites 

Ribosome and tRNA Molecules