Lecture 7 - Lecture 7 Here is a table that is trying to put...

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Lecture 7 Here is a table that is trying to put into context of how many of these organelles that we have in a cell. Number of mitochondria is very large (1700 in a liver cell). The other organelles occupy a small amount of volume (except for the ER) in a cell. There are a very large number of peroxisomes, lysosomes, and endosomes. These are membrane bound organelles. Comparison of peroxisomes, mitochondria and chloroplasts Mitochondria and chloroplasts have DNA. They have a genome and they can have multiple copies of the genome within the organelle. Peroxisome doesn’t have any DNA. They are oxidative organelles; they spend a lot of their times doing oxidation. M&C use chemiosmotic mechanism to make ATP. These organelles will import a large number of proteins through their membranes called translocation competent membranes. If we look at organelle genomes, mitochondria tend to have 37 genes, however they code for 850 proteins. But 37 genes can’t make 850 proteins. So obviously, there are a lot of proteins in a mitochondrion that are not the product of the mitochondrial genome. Chloroplasts have 110-120 genes and they can code for 88-100 proteins, but it turns out if you look inside a chloroplast, there are at least 3000 proteins, which are not coded for by these genes. If we look at the ancestor of chloroplast, cyanobactera, they have at least 1500 genes and they code for thousands of proteins. So after cyanobactera became a chloroplast, it lost a lot of genes and now codes for a small number of proteins. So there are a few genes in mitochondria, what do they code for? They code for components of the electron transport system (not all of them). For instance, look at cytochrome c oxidase, it is a very large multi-subunit part of the electron transport chain of the mitochondria. The mitochondrial genome codes for complex IV, all the rest are products of the cell’s nucleus and must move into the growing mitochondria in order for the electron transport chain to work. Same is true for complex III of the coenzyme Q, complex I of the NADH dehydrogenase. The mitochondrial genome is coding for a component of the electron transport chain, all the rest are coming from the nucleus. There are genes for rRNA because the mitochondrion codes for some of the ribosomal proteins and it also codes for a fair number of tRNA because as you know mitochondria is capable of making proteins. If mitochondria and chloroplasts originated from prokaryotes, why are they still there since the bulk of the proteins that they need are coded for by the host nucleus? Because there must be selective reasons. They want to reproduce and so they creep into the regulatory apparatus of the cell to make sure that they will be replicating as separate units and that they will not be lost completely. Now you could take every function coded for in the mitochondria or chloroplast and stick it into the nucleus and the whole ER could do electron transport. Are the organelles subject to selection? Yes.
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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 7 - Lecture 7 Here is a table that is trying to put...

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