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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.
| 16 | 00:01:12,000 | 00:01:14,000 | And although the plants themselves are different, |
| 13 | 00:01:15,000 | 00:01:20,000 | Here are the chromosomes and you can see on this one, and on this one… |
| 17 | 00:01:15,000 | 00:01:21,000 | the process of division is in fact very similar and this similarity is very important. |
| 11 | 00:01:19,000 | 00:01:22,000 | And now separation’s beginning. |
| 14 | 00:01:21,000 | 00:01:27,000 | First the cells from the culture, the cells that can make their own Tryptophan. |
| 14 | 00:01:21,000 | 00:01:26,000 | ..over here that the chromosomes are double along their whole length. |
| 15 | 00:01:27,000 | 00:01:32,000 | This is a consequence of the duplication that took place at the Interphase stage. |
| 15 | 00:01:28,000 | 00:01:33,000 | Now I’m flaming off this wire loop to sterilise it. |
| 16 | 00:01:32,000 | 00:01:35,000 | The doubleness of the chromosomes extends down their whole length… |
| 16 | 00:01:34,000 | 00:01:37,000 | In all bacteriological experiments we have to be careful that… |
| 12 | 00:01:34,000 | 00:01:39,000 | Chromosomes retreat to opposite ends of this dividing cell. |
| 17 | 00:01:36,000 | 00:01:41,000 | ..except for one special region, here is one such region… |
| 17 | 00:01:37,000 | 00:01:40,000 | ..we don't grow anything on our plates, we don’t get anything on our plates… |
| 18 | 00:01:41,000 | 00:01:45,000 | ..except the cells which we’re interested in and burning them off the… |
| 18 | 00:01:41,000 | 00:01:44,000 | ..and here on this chromosome another. |
| 19 | 00:01:45,000 | 00:01:49,000 | These special regions are called centromeres and they are in fact… |
| 13 | 00:01:45,000 | 00:01:49,000 | The arrow simply shows the direction of movement. |
| 19 | 00:01:46,000 | 00:01:50,000 | ..surfaces of things which will come in contact with the medium is the way we do it. |
| 20 | 00:01:50,000 | 00:01:56,000 | ..holding the double chromosome together. This stage is called Prophase. |
| 20 | 00:01:52,000 | 00:01:56,000 | So we take some cells from this culture and… |
| 14 | 00:01:52,000 | 00:01:55,000 | A new cell wall begins to be formed. |
| 15 | 00:01:57,000 | 00:02:00,000 | There it is, growing in from the edges. |
| 21 | 00:01:58,000 | 00:02:06,000 | ..streak them first on this plate and then on that one. |
| 21 | 00:01:58,000 | 00:02:03,000 | What happens next is that the chromosomes move together in the… |
| 16 | 00:02:01,000 | 00:02:05,000 | Chromosomes clump together, lose their structure, |
| 22 | 00:02:03,000 | 00:02:07,000 | ..centre of the cell and will line up across this equator. |
| 17 | 00:02:05,000 | 00:02:08,000 | as a new nuclear membrane forms around them. |
| 22 | 00:02:08,000 | 00:02:12,000 | And then we do the same with the cells from the other culture, |
| 23 | 00:02:09,000 | 00:02:16,000 | The centromere divides, setting the doubled chromosomes free in the cell. |
| 23 | 00:02:13,000 | 00:02:16,000 | the cells which cannot make their own Tryptophan. |
| 24 | 00:02:16,000 | 00:02:18,000 | Let’s see it happen. |
| 25 | 00:02:19,000 | 00:02:23,000 | Here you are, the chromosomes are unravelling, becoming shorter and thicker, |
| 26 | 00:02:29,000 | 00:02:32,000 | and are now beginning to line up. |
| 24 | 00:02:34,000 | 00:02:41,000 | Now, how do we tell whether the cells are able to make their Tryptophan or not? |
| 27 | 00:02:39,000 | 00:02:43,000 | There. Now here’s the same cell again and there’s the equator… |
| 25 | 00:02:42,000 | 00:02:46,000 | Well if they can make Tryptophan they will be able to grow on the medium which… |
| 28 | 00:02:44,000 | 00:02:47,000 | ..along which the cell, the chromosomes are aligned. |
| 26 | 00:02:47,000 | 00:02:52,000 | ..contains none and to find this out we will have to incubate the plates for a time. |
| 29 | 00:02:48,000 | 00:02:53,000 | The centromeres divide, though you can’t see that on the photograph, |
| 27 | 00:02:53,000 | 00:02:57,000 | Well we haven’t got time to wait so I have some dishes to show you… |
| 30 | 00:02:54,000 | 00:02:57,000 | and this stage is called Metaphase. |
| 28 | 00:02:57,000 | 00:03:00,000 | ..which were streaked out a couple of days ago. |
| 31 | 00:02:58,000 | 00:03:01,000 | The next stages happen quite quickly. |
| 29 | 00:03:00,000 | 00:03:04,000 | They’ve been in this incubator and the cells have been growing. |
| 32 | 00:03:02,000 | 00:03:05,000 | The now separated parts of the chromosome move, |
| 33 | 00:03:06,000 | 00:03:09,000 | one to this end, and one to that end of the cell. |
| 30 | 00:03:07,000 | 00:03:14,000 | First of all, here is the dish which contained a medium which had Tryptophan added to it. |
| 34 | 00:03:10,000 | 00:03:15,000 | At the same time, a new cell wall will become visible forming across the equator. |
| 31 | 00:03:15,000 | 00:03:20,000 | I’ll put it up so that you can see what’s happened. |
| 35 | 00:03:17,000 | 00:03:21,000 | And also around the chromosomes at the ends of the… |
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