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7. Eukaryotic Gene Structure and Noncoding DNA.pdf

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Biology (Sci)
BIOL 200
Richard Roy

Naveen Sooknanan McGill Fall 2011 Eukaryotic Gene Structure and Noncoding DNA: The eukaryotic genome is made up of double stranded DNA (dsDNA), as opposed to single stranded DNA (ssDNA), which is linear (as opposed to the circular DNA of prokaryotes). DNA is measures in base pairs, bp, but due to the length of many DNA strands, more common notations are kilobase pairs (kbp) which are 1000 base pairs or megabase pairs (mbp) which are 1,000,000 base pairs.  Viruses like HIV have a tiny genome length of 0.009 mbp  Prokaryotes generally have smaller genomes than eukaryotes, but larger than viruses. The genome size of E. coli is 4.6 mbp  Eukaryotic genomes vary greatly in size. A yeast genome, one of the smallest eukaryotic genomes, is 12 mbp. The human genome us 3300 mbp. Contrary to logic, the tulip genome is enormous, around 33000 mbp and the Amoeba Dubia genome is even larger, around 660000 mbp This shows that the complexity of the organism does not directly relate to the genome size. In fact, the number of genes in these organisms is relatively similar, but the amount of noncoding DNA varies a lot.  Taking 50 kbp fragments of yeast, a more complex eukaryote and a human, it is clear that more complex organisms have much more noncoding regions in the same amount of DNA o Introns in humans are much larger than those in yeast o Lower number of genes in the same size DNA fragment The definition of a gene is the entire nucleic acid sequence that is necessary for the synthesis of a functional gene product  A polypeptide or RNA o tRNA and rRNA are final gene products, because they don’t undergo translation In eukaryotes, genes are expressed in sequences of DNA called transcription units  The exons are the coding regions of the transcription unit which are transcribed into mRNA o The coding region is also known as the Open Reading Frame (ORF)  The control regions of the transcription unit can be enhancer, silencers and other cis regulatory factors o The distance between control regions can be as long as 50 kbp o By algorithms, it is possible to find the locations of control regions closest to the exons but it is much more diffcullt to locate the distal control region o Many control
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