Lecture 6 - Lecture 6 How many molecules of DNA are in one...

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Lecture 6 How many molecules of DNA are in one typical human nucleus? There is not a lot of chromosomes (96 in M phase after G2, 46 in interphase) but there is a lot of DNA in the cell. Each chromosome is one huge molecule of DNA. Chromosome vs. genome We live in a post-genomic era, which means that we know the sequence of our whole genome. Q: Which of the following is false? A: Most of the DNA in the human genome encodes functional gene products, including proteins. Most of the DNA in the human genome has no known function, even though approximately half appears to be transcribed into RNA (at least at some point). The idea is that DNA is being made into RNA implies some function to those pieces of DNA even though we cannot recognize particular protein associated with those sequences. Huge variation in the density of genes in 90,000 bp of DNA of 4 organisms: This is a stretch illustrated by the line here, about 90,000 bp of DNA. This is a protein coding sequence (little red parts) that you can predict mapped onto that DNA. You can see that the vast majority of the space in B.subtilis bacteria, S. cervisiae yeast, and D. melanogaster (Drosophila) is taken up by the sequence on which we can map known proteins. So we know that this DNA encodes a protein (central dogma DNA => eventually a protein). Case of the human genome, however, is completely different. Top line is a much larger stretch; it’s 500,000 bp. You can see that most of encodes no proteins. It doesn’t mean that it’s not transcribed into RNA. Even intragene sequences are getting transcribed at some level. We now know that they encode non-coding RNAs, mRNAs or transcripts of unknown functions. Presumably that’s why we are more complex than yeast or a bacteria. Comparing genome size and gene numbers Considering all these change in the genome, there isn’t the big difference in the amount of protein genes present. Ex. Yeast has~ 6,000 genes with 14,000 bp genome. You increase the size of genome dramatically to human (3.1x10^9) you only have only a 4 fold increase in the number of genes. Presumably, all the extra stuff contributed to the complexity of the organism. Compared to rice, which has a 10 fold smaller genome and about the same # of protein-coding genes as humans. Comparing genome and gene information=> hard to know what is going on. Transposable element in the human genome: Why is there so much “extra stuff” in human genome? One of the answers: transposable elements. Transposons are the pieces of DNA that can move around in the genome. You can identify them by the known sequences. And when you look at whole genome you find them all over the place in relatively random fashion. In humans there are 3 kinds to focus at: L1, Alu or SVA elements. They act like a gene. They can encode an mRNA that will make a protein. Considering how many of the transposable elements are in the
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This note was uploaded on 09/14/2011 for the course BIO 310 taught by Professor Lyman during the Spring '08 term at SUNY Stony Brook.

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Lecture 6 - Lecture 6 How many molecules of DNA are in one...

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