Lecture 9- eukaryotic molecular genetics

Lecture 9- eukaryotic molecular genetics - When discussing...

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When discussing the genetic code we made much of the fact that the code is universal as is (mostly) the central dogma. We also have now looked into the organization and regulation of genes in prokaryotes (specifically the bacterium E. coli ). It is easy to see why there was the expectation among scientists that the organization of eukaryotic genes would be very similar. They were in for a surprise. When people began the molecular analysis of eukaryotic DNA, they found something very odd. There seemed to be a lot more DNA than was needed for the genes that needed to be encoded. Typhus has ~1.1 million base pairs and about 800 genes whereas people have ~30,000 genes but 3,000 million base pairs. It would seem that we have 100 times as much DNA as we need to encode all of our genes. Let's look at the typhus genome again. The genes are packed in like sardines with basically just enough room between them for a promoter and maybe an operator. Very efficient, which is what one might expect from an organism that is under pressure to reproduce rapidly when times are good. Let's look at a stretch of human DNA. We will use the human genome database at www.ncbi.nlm.nih.gov. Specifically, we will look at the region in which resides the green opsin/pigment gene that is defective in colorblindness.
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So the genes are the jagged lines and, as before, they are transcribed from both strands as indicated by the fact that they are on both sides of the scale bar. The scale bar indicates thousands of base pairs. Notice there is a lot of space between the genes. Now lets zoom in on the opsin gene.
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The opsin gene is represented by the squares connected by zig-zag lines. This region of DNA that is transcribed from top to bottom. However, if you use the protein sequence of opsin to deduce which part of the gene codes for protein, you find that only the part indicated by the blue squares is coding. These are called the exons . Let's zoom in again and look at the sequence of the second exon from the top.
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The part of the DNA that constitutes the protein-coding exon is outlined in blue. How is
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This note was uploaded on 04/07/2010 for the course BIOL biol 112 taught by Professor Dent during the Winter '10 term at McGill.

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Lecture 9- eukaryotic molecular genetics - When discussing...

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