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Evidence that DNA is genetic material 1

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- One criterion that we use to define biological life, is that the organism must have the ability to reproduce. And the parent organism... Must have the ability to pass on to its offspring... Some sort of material that contains the instructions for living, and we call this material genetic material. What is genetic material? Well, today we know that it's DNA, or deoxyribonucleic acid. But this wasn't always so obvious. We're going to go through a couple of earlier experiments that helped prove to us that DNA is genetic material. The first experiment we're going to discuss, was one that was conducted by a scientist by the name of Friedrich Miescher. And Miescher lived from 1844 to 1895. And Miescher worked with cells that he took out of pus, and today we know that these are lymphocytes. And lymphocytes happen to have very large nuclei, so if that's the cell, the nucleus might look something like that. And of course, there's this material inside the nucleus. And because the nuclei are so large, Miescher was able to isolate the material inside the nucleus. And he analyzed this material, and came to the conclusion that it was made up of two components. The first was protein. And the second was this substance that acted like an acid, and so he called it nucleic acid. Nucleic because it came from the nucleus. And so Miescher was the first one to isolate and identify nucleic acid. The next experiment we're going to talk about was one conducted by a scientist who lived at about the same time. His name was Wilhelm Roux. And he lived from 1850... To 1924... And Roux worked with cells that were dividing, and he analyzed these cells, so I drew a cell here, and I drew a couple of the organelles also, let's just label them. We have the endoplasmic reticulum here, we have a couple of mitochondria. And the singular is mitochondrion. And then we have a couple of ribosomes, I'm just going to abbreviate it like that. And I also drew some vesicles. And of course, in the center, we have the nucleus. And we're going to see that this cell is undergoing mitosis right now, so I'm going to draw the chromosomes like that in the center, I'm going to draw four chromosomes. And I'm also going to draw the mitotic spindle. which will help to separate the chromosomes into the two cells that are being formed. And what Roux noticed, was that when the cell divided, so the organelles were not necessarily distributed in a very organized and even fashion, you can see the cell on the left got three mitochondria, the cell on the right only got two, the cell on the left got three ribosomes, the one on the right only got two, but he noticed that the material in the nucleus divided in an extremely organized fashion, so each nucleus got exactly four chromosomes. And so Roux concluded that because the material in the nucleus was divided in a very orderly and even fashion, that that must be the genetic material. And this makes sense, because the genetic material or instructions for living, is the most important thing that the parent cell has to pass on to the daughter cell. If one of the daughter cells didn't get enough mitochondria, well, that's not so terrible, as long as it has the correct instructions for living, it can make more mitochondria. If one of the cells accidentally didn't get a ribosome, well, if it has the right instructions for living, it can make ribosomes. So the conclusion here, was that genetic material is made up of protein... And, or, nucleic acid. This was the conclusion that Friedrich Miescher's, experiment and Roux's experiment helped prove.