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Description
This unit is concerned with the cell nucleus. The different stages of mitosis are pointed out and explained by Stephen Hurry. Michael Pentz briefly takes up the topic of nucleic acid as a short int
...roduction to B.S. Cox's experiment in DNA transformation. Cox explains the controls needed to perform the experiment and shows what happened to the controls during the experiment.
| 32 | 00:03:21,000 | 00:03:26,000 | You will notice that there is a substantial bacterial growth on both sides of the plate. |
| 36 | 00:03:21,000 | 00:03:25,000 | ..daughter cells a new nuclear membrane will appear. |
| 37 | 00:03:26,000 | 00:03:30,000 | Now you can see this if you watch not only this cell but this one… |
| 33 | 00:03:27,000 | 00:03:30,000 | Cells of both cultures have been able to grow on this medium. |
| 38 | 00:03:30,000 | 00:03:34,000 | ..and this one, all three at the same time, for in these two cells… |
| 34 | 00:03:32,000 | 00:03:35,000 | Now here is the other plate, the one which contains a medium that has… |
| 35 | 00:03:35,000 | 00:03:39,000 | ..no Tryptophan in it and you will see that there is a growth on only… |
| 39 | 00:03:35,000 | 00:03:40,000 | ..the process is slightly in advance of the process in this big cell. |
| 36 | 00:03:40,000 | 00:03:43,000 | ..one side of the plate, the side where we put… |
| 40 | 00:03:41,000 | 00:03:43,000 | So let’s see that happen. |
| 37 | 00:03:43,000 | 00:03:46,000 | ..cells from the culture which could make its own Tryptophan. |
| 41 | 00:03:45,000 | 00:03:50,000 | Now the chromosomes are separating, some of them… |
| 38 | 00:03:46,000 | 00:03:48,000 | The cells from the other culture on the other side of the plate have been… |
| 39 | 00:03:49,000 | 00:03:53,000 | ..unable to grow, they need that Tryptophan, they can’t make it so they can’t grow. |
| 42 | 00:03:51,000 | 00:03:54,000 | ..fairly reluctantly as if the chromosomes were sticking together. |
| 40 | 00:03:55,000 | 00:04:02,000 | Well now, what we’re going to try and do is transform these cells, |
| 43 | 00:03:58,000 | 00:04:03,000 | There they go and the last one. An arrow will appear in a moment… |
| 41 | 00:04:03,000 | 00:04:07,000 | the ones which cannot make their own Tryptophan into cells which can make Tryptophan. |
| 44 | 00:04:04,000 | 00:04:11,000 | ..simply to show the direction of movement. There it is. |
| 42 | 00:04:08,000 | 00:04:11,000 | To do this we have to transfer the ability to make Tryptophan… |
| 43 | 00:04:12,000 | 00:04:16,000 | ..from cells which can make it. And as we think that the DNA is… |
| 45 | 00:04:12,000 | 00:04:15,000 | Now you can begin to see the beginnings of the cell wall… |
| 46 | 00:04:16,000 | 00:04:23,000 | ..forming across the middle, growing inwards from the edges. |
| 44 | 00:04:17,000 | 00:04:21,000 | ..the material which will give the cells this information we have to… |
| 45 | 00:04:22,000 | 00:04:27,000 | ..extract the DNA from these cells, the ones which are able to make their own Tryptophan. |
| 46 | 00:04:29,000 | 00:04:32,000 | Now this is quite a lengthy process and we haven’t got time to show you the whole of it. |
| 47 | 00:04:29,000 | 00:04:32,000 | The cell wall’s very distinct now. |
| 47 | 00:04:34,000 | 00:04:38,000 | We start off by breaking open the cells with an enzyme called Lysozyme. |
| 48 | 00:04:35,000 | 00:04:38,000 | Here are the last stages in the division of the cell. |
| 48 | 00:04:39,000 | 00:04:42,000 | And then we go through a chemical procedure which is relatively simple… |
| 49 | 00:04:39,000 | 00:04:42,000 | In this cell the chromosomes have retreated to the ends of the daughter cells. |
| 49 | 00:04:43,000 | 00:04:50,000 | ..and we end up with a cell extract which contains a solution of DNA and… |
| 50 | 00:04:43,000 | 00:04:46,000 | A new cell wall is forming between them and… |
| 51 | 00:04:47,000 | 00:04:51,000 | ..in these two cells the final stages can be seen. |
| 50 | 00:04:51,000 | 00:04:56,000 | ..various other cell products and what we want to do is a final stage |
| 52 | 00:04:52,000 | 00:04:55,000 | Notice that the structure of the chromosomes is being lost and… |
| 53 | 00:04:56,000 | 00:04:59,000 | ..in this lower nucleus, even less of the chromosomes can be seen. |
| 51 | 00:04:57,000 | 00:05:02,000 | ..is remove the DNA from the solution, so that we end up… |
| 54 | 00:05:00,000 | 00:05:03,000 | And around each, a new nuclear membrane will be forming. |
| 52 | 00:05:03,000 | 00:05:07,000 | ..with a purified DNA solution from these cells. |
| 55 | 00:05:04,000 | 00:05:08,000 | Daughter cells, each now with their own nucleus and separated… |
| 53 | 00:05:08,000 | 00:05:13,000 | And to do this we precipitate the DNA out of solution using alcohol. |
| 56 | 00:05:09,000 | 00:05:13,000 | ..by a cell wall, so that we have two cells where we started with one. |
| 54 | 00:05:14,000 | 00:05:26,000 | We carefully layer alcohol on top of our cell extract and we get… |
| 55 | 00:05:28,000 | 00:05:35,000 | ..two layers of liquid, the cell extract at the bottom and the alcohol layer on top… |
| 56 | 00:05:36,000 | 00:05:41,000 | ..and where the two layers meet, a cloudy precipitate forms and the DNA molecule… |
| 57 | 00:05:42,000 | 00:05:47,000 | ..is a fibre so the precipitate is a fibrous precipitate and… |
| 58 | 00:05:48,000 | 00:05:52,000 | ..we can collect it by spooling it onto a glass rod. |
| 59 | 00:05:56,000 | 00:06:00,000 | There it is spooled on the glass rod and now we dissolve off… |
| 60 | 00:06:01,000 | 00:06:08,000 | ..the spooled fibres from the glass rod in a sterile dilute salt solution. |
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