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Lecture 11

Biology 1002B lecture 11

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Biology 1002B
Tom Haffie

Lecture 11 ?????relative sizes of typical mitochondrial, chloroplast and nuclear genomes - The nuclear genome has the largest genome by far (orders of magnitude bigger), the chloroplast has much fewer base pairs (about 200 kb) with the mitochondrion having the fewest base pairs (about 16 kb) - The typical prokaryote E. Coli has a much bigger genome than that of the organelles. This suggests that lateral gene transfer has occurred, making the genome in the organelles much smaller than expected for a typical prokaryotic cell -Clamey has 100 thousand kilabases (100 thousand base pairs) - linear chromosomes - chloroplast has dna in it, only 200 kilabases. -Vaucheria litorea (chloroplast genome) - its an algae -170 genes, 115kb of dna - this genomes has gone from 5000 kilabases down to 115 over evolutionary time. -We make only about a dozen proteins but they put 37 genes, why? -Why is there a disconnect b/w number of gnes and number of proteins? - not all protein coding genes (junk dna, dead) - If gnes don’t code for proteins what do they code for? All rna’s are made by transcrption of genes. Each of different rna’s have own gene. Might be protein coding gene or might be rna coding gene. Most genes code for rna. Why? ****rubisco structure and assembly from components coded by different genomes - the enzyme usually consists of two types of protein subunit, called the large chain L and the small chain S. The large-chain gene is part of the chloroplast DNA molecule in plants. possible reasons why modern organelle genomes have become dramatically smaller over evolutionary time - Thye’ve evolved to be very specific, they only carry certain processes so they don’t need any gnes? Where do they go? - genomes have been deleted. - Hosts in which their mitochondria has suffered a mutation and deletion, those genomes will be easier to replicate (selective advantage) selection favouring organelles getting rid of all the genes they can. - Some genes are useful for free living bacteria but when mitochondria and chloroplasts were absorbed into the early eukaryote, some genes became redundant (like those for flagella and glycolysis)  Selection then favoured organelles with streamlined genomes because they are more efficient and use less energy to replicate and translate their genomes - Why would a cell want two copies of everything? Why would genes take two copies for mito and nucleus (a lot of redundancy) . possible reasons why genes have moved to the nucleus from organelles over evolutionary time 1. Coordinated control between the nucleus and the organelles - why in general want to get dna out of mitochondria and chloroplast? 2. Mitochondria and chloroplast are involved in electron transport and oxygen metabolism that generates reactive oxygen species. Oxygen + electron gives reactive oxygen species. - These organelles are sites of ROS production and ROS is very reactive and very mutagenic and creates all kids of damage in dna. Makes sense to get dna out of the mutagenic oxygen.- what denis taught but haffies doesn’t agree 3. RNA can be edited in the nucleus though it cannot be edited in the organelles (no separation between DNA and ribosomes so translation directly after transcription) - organelle genomes are
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