6. To study one form of cancer that seemed to be inherited,...

6. To study one form of cancer that seemed to be inherited, researchers did a set of experiments to characterize the behavior of cell samples from patients who had a family history of the disease ("study group"). As a control in their experiment, the researchers also obtained cell samples from people in the general population who have no family history of cancer ("normal group"). They exposed one set of cells to UV light, which is known to interfere with DNA replication. The other set they left untreated. The researchers compared percentages of cells in interphase and mitosis (Table 1), as well as the DNA content in the interphase cells (Table 2), and got the following results: Untreated Treated with UV % cells in: Normal Group Study Group Normal Group Study Group Interphase 50 51 90 50 Mitosis 50 49 10 50 Table 1. Percentages of untreated and UV-treated cells in interphase and mitosis Untreated Treated with UV % of interphase cells with: Normal Group Study Group Normal Group Study Group 1X DNA content 43 44 64 40 1.5X DNA content 9 7 14 12 2X DNA content 48 49 22 48 Table 2. Percentages of untreated and UV-treated cells with 1X (normal), 1.5X, and 2X DNA content Based on this data, explain at least one mechanism that might be responsible for the increased cancer risk in these patients. Your answer should discuss what is happening with regard to the cell cycle in the normal group, and why the study group data is different.

Transcript

00:01 Form of cancer that seemed to be inherited, research did a set of experiments.

00:05 So you have two groups.

00:06 One is normal group, which has no family history of cancer.

00:22 And you also have a study group with cancer family history.

00:36 So these two groups were actually tested for different experiments.

00:42 One is to test the ratio of interphase and mitosis, number of cells in interphase and mitosis phase with and without a treatment for uv.

00:54 And the other experiment, table number two, shows the content of a dna, 1x, 1 .5x, and 2x dna during interphase.

01:05 So based on the data, explain at least one mechanism that may be responsible for the increased cancer risk.

01:11 Let's take a look at table one.

01:19 So for table one, you can see that with untreated, with uv, the percentage of cell in interphase and mitosis, they are pretty close.

01:34 They are 50 -50.

01:35 And this is the same with the normal, which is control versus the study.

01:49 This is a test group.

01:52 So basically you've got 50 % similar enough, which is 51 % versus 49%.

02:03 So basically you have equal number of cells that are during the interphase and mitosis.

02:09 But since it's treated with uv, and you can see that for the normal cell, you have a lot more halted in interphase.

02:25 90 % is interphase and 10 % is in mitosis.

02:32 If you look at the study group, the ratio is still 50 -50.

02:40 So what does this piece of data tell us? so this means that in normal cell, uv disrupt dna and causes mutation.

03:16 So these mutations triggered the dna damage monitoring system and repair system.

03:58 So the dna damage detector repair system are called checkpoint.

04:02 So this checkpoint will try to repair dna.

04:06 So if the dna caused by the uv is too severe and the damage cannot be repaired, the system will hold or halt the cell in the interphase and prevent it from going into mitosis.

04:22 So we call this checkpoint mechanism, hold damaged cell so they don't go into mitosis.

04:55 Reduce the amount of cell, number of cell that can enter mitosis.

05:14 Because in those cells, the dna replication cannot be done properly.

05:18 And the cell also know that due to the damaged dna, that the mitosis is not going to happen normally to prevent the cell to become a cancerous cell.

05:32 The checkpoint mechanism will prevent the damaged cell from entering the mitosis.

05:39 So this is why we see a reduced number of cell that goes into the mitosis.

05:44 You can see that now you only have 10 % of the cell that are able to enter the mitosis.

05:51 The rest of others, because they have mutations, so the normal cell, they have damaged the dna damage repair system to try to repair it or prevent it from entering the mitosis.

06:07 In the study cell, this dna damage repair system is probably disrupted.

06:48 So in study cell, the dna damage detect and repair system is faulty.

06:52 So even though the uv light disrupt dna caused a lot of damage, which lead to mutations, the cell still go ahead to enter mitosis.

07:21 So the number of cell that are halted during the interface is actually the same as the one that without damage...

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