The Structure of Ribosomal RNA

(Cooper, 1997 p. 277-288 ) 

 
The ribosome is the site where mRNA is translated into protein. It brings together the tRNAs, mRNAs, and specific amino acids.

Classification and Component Structure

 Ribosomes are composed of 2 subunits a large subunit and a small subunit.

 Prokaryotic ribosomes differ from eukaryotic ribosomes as shown in Fig. 1. The ribosomes and ribosomal subunits are described in terms of their approximate rate of sedimentation (in Svedberg units). The higher the mass of the particle the higher the s value and the greater the rate of sedimentation.

 
Function of Ribosomes

The ribosome serves as the site of protein synthesis. mRNAs, tRNAs, and amino acids are brought together.

On the ribosome, the mRNA fits between the two subunits (the interactions are stabilized by interchain hydrogen bonding). The tRNAs occupy a site on the large ribosomal subunit.

 The ribosome attaches to the mRNA at or near the 5'end.

  • In prokaryotes there is a ribosome binding site near the 5'end of the mRNA.
  • In eukaryotes, the ribosome first attaches at the 5'CAP (7-methyl guanosine).

    •  The ribosome then moves along the mRNA in the 5' to 3' direction, one codon at a time.

     

    References:
    Cooper, Geoffrey M. (1997) The Cell: A Molecular Approach; ASM Press, Washington, D.C. / Sinauer Associates, Inc., Sunderland, MA.