DNA and the Genome Key Area 3 d

DNA and the Genome Key Area 3 d Alternative RNA Splicing

Learning Intentions Expressing different proteins from one gene Explain the mechanism by which different proteins can be expressed from one gene Define ‘alternative RNA splicing’ • Explain why many different m. RNA molecules are produced from the same primary transcript

One Gene…Many Proteins Alternative RNA Splicing

One gene…many proteins Different proteins can be expressed from one gene as a result of: Alternative RNA splicing

Genes to Proteins The human genome is thought to contain between 20, 000 – 25, 000 genes but there are over 100, 000 different proteins present in the human body How then is it possible to produce all of these proteins? The answer lies in the fact that some genes are able to produce more than one protein due to the process of alternative RNA splicing Different m. RNA molecules are produced from the same primary transcript depending on which RNA segments are treated as exons and introns and which combination of exons are included in the mature RNA transcript

Alternative RNA Splicing There are different methods of combining exons when they are spliced from the primary m. RNA transcript: 1. Exon skipping – different exons are removed or included. 2. Mutually exclusive exons – one of two exons may be included but not both Different mature m. RNA transcripts are produced from the same primary m. RNA transcript depending on which exons are retained

Exon Skipping 2 different mature m. RNAs can be produced depending on which exons are included (or excluded). The order of exons never changes!

Mutually Exclusive Exons Only 1 of the 2 exons (shown in orange and green) can be included to make the mature m. RNA

Alternative splicing animation

Two antibodies from one gene – an example This diagram shows how 2 antibodies with different structures can be made from the one gene via alternative splicing The antibody on the left has the exon for membrane binding present (and secreted exon cut out) and so it is found on the cell membrane of a white blood cell The antibody on the right has had the secreted exon present (and the membrane bound exon spliced out) and so is found free in the bloodstream