• Ribosomes are?small organelles?that are either?free?in the cytoplasm (of all cells) or are attached to the?rough endoplasmic reticulum?(only in eukaryotic cells)
• Ribosomes are the site of?protein synthesis?(where proteins are made)
  • They ‘read’ RNA to make polypeptides (proteins) in a process known as?translation

   

• Ribosomes are themselves?formed from RNA and proteins
  • The RNA that forms part of the structure of ribosomes is a specific type of RNA known as?ribosomal RNA?(rRNA)
  • The?rRNA?in ribosomes has?enzymatic properties?that catalyse the formation of peptide bonds between amino acids
  • Each ribosome is a?mixture?of?ribosomal RNA?and?proteins

   

• Ribosomes in eukaryotic cells are?larger?than those in prokaryotic cells. In?both cell types, ribosomes are composed of a?small subunit?and a?large subunit
  • 80S?ribosomes (composed of 60S and 40S subunits) are found in?eukaryotic cells
  • 70S? ribosomes (composed of 50S and 30S subunits) are found in?prokaryotic cells, as well as in the?mitochondria?and?chloroplasts?of eukaryotic cells

   

• The?large subunit?is the?site of translation
  • The rRNA and proteins of the large subunit hold tRNA molecules (with their attached amino acids) in place
  • rRNA can then catalyse the condensation reactions between amino acids

   

• mRNA sits between the two subunits?and the ribosome moves along it as it translates it into a polypeptide
• Unlike some organelles, ribosomes are?not surrounded by a membrane

A diagram of a ribosome, showing the small and large subunits