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Cell Biology


In 1993 Phillip Sharp and Richard J. Roberts were awarded the Nobel Prize in Physiology and Medicine for the discovery of introns and splicing. Splicing in the nucleus is carried out by a molecular machine known as the spliceosome.

The spliceosome is made up of five small nuclear RNAs (snRNA) and associated proteins to form an RNA-protein complex (snRNP). This molecular machine carries out the removal from pre-mRNA of a number of stretches of code which are not required for a specific protein’s construction. These unwanted pieces of code are called introns which means intragenic region. Exon stands for executed region, the functional sequence that is left behind.

A spliceosome assembles on the pre-mRNA molecule at each exon: intron junction.  To facilitate this process, a specific sequence element in the intron signals to a spliceosome to assemble at that site. The spliceosome then cuts out the intron from the chain and ties together the remaining functional pieces of RNA (exons). The interesting thing is that on different occasions the same strand of pre-mRNA may have different introns cut out of it to assemble different proteins!

The overall complexity of the spliceosome is amazing.  Not only must these machines function at a huge number of action sites (about 8 introns per gene), but they must be accurate. A mistake in only 1 nucleotide could be disastrous.

How these tiny molecular machines identify the correct points along a pre-mRNA chain, cut out specific introns, splice together the remaining cut ends, and do this at different sites along the chain for a variety of proteins is totally amazing.  Can you imagine how such a system could ever initially form as a result of spontaneous processes? Any cells attempting to develop such a system would shortly be dead in the water! This is the kind of finesse in planning we see from the Creator!

Related Terms

  • Alternative Splicing
  • RNA (Ribonucleic Acid)
  • Amino Acid and Proteins
  • Intron
  • Exon