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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.
| 61 | 00:06:11,000 | 00:06:17,000 | Now then, in that solution we have purified DNA molecules… |
| 62 | 00:06:18,000 | 00:06:20,000 | ..from cells which were able to make their own Tryptophan. |
| 63 | 00:06:22,000 | 00:06:27,000 | What have we to do? Well the experiment is to see whether these cells… |
| 64 | 00:06:28,000 | 00:06:33,000 | ..which cannot make their own Tryptophan, will take up DNA and use it… |
| 65 | 00:06:34,000 | 00:06:37,000 | ..to provide information which will enable them to make Tryptophan. |
| 66 | 00:06:38,000 | 00:06:43,000 | So we add some of this sterile DNA, purified DNA solution - |
| 67 | 00:06:48,000 | 00:06:53,000 | one millilitre will do - to these cells, keeping them sterile… |
| 68 | 00:06:59,000 | 00:07:02,000 | ..and we let the mix stand for a time. |
| 69 | 00:07:03,000 | 00:07:09,000 | Now what we have to find out is whether any of the… |
| 70 | 00:07:10,000 | 00:07:15,000 | ..cells in that mix acquire the ability to make Tryptophan. |
| 71 | 00:07:16,000 | 00:07:19,000 | And how do we do that? Well you know the answer. |
| 72 | 00:07:20,000 | 00:07:23,000 | We have a medium which can tell us whether they’re going to make Tryptophan. |
| 73 | 00:07:26,000 | 00:07:31,000 | Here is a dish of that medium and what we have to do obviously, |
| 74 | 00:07:32,000 | 00:07:36,000 | is place some of these cells on the medium and see whether any of them can grow. |
| 75 | 00:07:57,000 | 00:08:02,000 | We take a tenth of a millilitre, pipette it on the surface of the plate… |
| 76 | 00:08:03,000 | 00:08:05,000 | ..and then we can spread the cells evenly all over… |
| 77 | 00:08:06,000 | 00:08:08,000 | ..the surface of the plate with a sterile glass rod. |
| 78 | 00:08:10,000 | 00:08:16,000 | Cool it down first. There we are. |
| 79 | 00:08:18,000 | 00:08:22,000 | Now again it’ll be two days before we can see whether any cells are… |
| 80 | 00:08:23,000 | 00:08:25,000 | ..able to make their own Tryptophan because they have to incubate. |
| 81 | 00:08:26,000 | 00:08:30,000 | And again we have some plates to show you which were plated out two days ago. |
| 82 | 00:08:31,000 | 00:08:34,000 | But before I show you them, there are two controls which are… |
| 83 | 00:08:35,000 | 00:08:40,000 | ..needed to establish this experiment and you ought to be thinking about… |
| 84 | 00:08:41,000 | 00:08:44,000 | ..what those controls are while I’m getting the plates out of the incubator. |
| 85 | 00:08:47,000 | 00:08:54,000 | Well first of all, here is the plate from two days ago on which we plated out… |
| 86 | 00:08:55,000 | 00:08:58,000 | ..the mix, the mix of cells which are unable to make their own Tryptophan… |
| 87 | 00:08:59,000 | 00:09:02,000 | ..plus DNA extracted from the other kind of cells. |
| 88 | 00:09:11,000 | 00:09:21,000 | Now, you can see, all over the surface of this plate, a number of colonies have grown. |
| 89 | 00:09:22,000 | 00:09:27,000 | Each of those colonies contains about a thousand million cells but each… |
| 90 | 00:09:28,000 | 00:09:33,000 | ..has grown from a single cell, a cell which has acquired the ability to make Tryptophan. |
| 91 | 00:09:35,000 | 00:09:42,000 | And these cells were from the mix of DNA plus cells that were unable to make Tryptophan. |
| 92 | 00:09:45,000 | 00:09:51,000 | Now what about those controls? Well clearly we need to establish that neither the DNA… |
| 93 | 00:09:52,000 | 00:09:57,000 | ..nor those cells in the mix were alone able to grow on this sort of medium. |
| 94 | 00:10:00,000 | 00:10:10,000 | So here we have the control plates. First of all, the DNA, and secondly, |
| 95 | 00:10:11,000 | 00:10:16,000 | the cells alone and on neither of these plates has any growth occurred. |
| 96 | 00:10:18,000 | 00:10:24,000 | Now what this experiment establishes is that DNA can be transferred from… |
| 97 | 00:10:25,000 | 00:10:30,000 | ..one kind of cell to another and that it can carry with it information… |
| 98 | 00:10:31,000 | 00:10:35,000 | ..which makes a difference between those two cells. In this case it… |
| 99 | 00:10:36,000 | 00:10:40,000 | ..carries information which enables these cells to make… |
| 100 | 00:10:41,000 | 00:10:43,000 | ..an enzyme which will allow them to make Tryptophan. |
| 101 | 00:10:44,000 | 00:10:49,000 | We can infer from the results on this plate, one more thing about… |
| 102 | 00:10:50,000 | 00:10:56,000 | ..the function of DNA and that is that this information has been inherited, |
| 103 | 00:10:57,000 | 00:11:00,000 | has been passed on from the original cell which… |
| 104 | 00:11:01,000 | 00:11:03,000 | ..acquired the ability to make Tryptophan to all its progeny. |
| 105 | 00:11:04,000 | 00:11:09,000 | If it were not passed on to its progeny we would simply not get colonies of this size. |
| 106 | 00:11:10,000 | 00:11:13,000 | There are too many cells, it would require too many divisions of a… |
| 107 | 00:11:14,000 | 00:11:17,000 | ..single cell to produce that amount of growth, ten to the nine divisions to be precise. |
| 108 | 00:11:18,000 | 00:11:23,000 | And in any case, we can test quite easily whether all the cells in those colonies… |
| 109 | 00:11:24,000 | 00:11:30,000 | ..can make Tryptophan, and they can, and you ought to know by now how to do that test. |
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