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Cell Biology

Alternative Splicing

One of the last of the loose ends from the Human Genome Project was the publication of the features of individual chromosomes. This process came to an end on May 18, 2006 with a published description of the last, and the longest, of the chromosomes: human chromosome number 1. Not too surprisingly, this chromosome contains the largest amount of information. One newly discovered phenomenon, particularly noted on chromsomes 1 and 11, was the existence of overlapping genes. This is where part of the coding sequence for one gene also forms part of the coding sequence for an adjacent gene. This discovery demonstrates that genes are not discrete units, but contain continuous blocks of information.

Another strange phenomenon, very apparent on chromosome number 1 as well as on others, is “alternative splicing of genes.” The normal splicing involves the copying of a block of DNA code. The process is, however, more complicated because it also involves special enzymes, the spliceosomes which chop out large chunks of information. The removed chunks are called introns while the remaining sections are called exons. Exons may be glued together by other enzymes or by the spliceosome. Some of these joined exons may come from stretches of DNA far away from others. The opportunities for variation are obvious. Each small section of code can be used in many different genes.

The capacity for the cell to synthesize different proteins from the same block of information is stupendous. This phenomenon represents highly compressed information. Considering how every protein must be extremely precisely produced, this storage and retrieval system is indeed an impressive mark of design. How can anyone believe that a spontaneous process could produce these wonders?

Related Terms

  • Spliceosome
  • Intron
  • Exon
  • Human Genome Project (HGP)