Week 4 - Cell Cycle 1

Front 1

What are the three states cells in your body can be in? Gives examples

Back 1

Always dividing (crypt cells in intestine), never dividing again (RBCs, neurons), or "resting" (mammary cells, which divide in response to hormones)

Front 2

What are the two musts of cell division?

Back 2

1. The cell must replicate its DNA once and only once
2. The cell must accurately partition its DNA between two sibling cells

Front 3

How can you tell a cell is in mitosis by looking at it in tissue culture?

Back 3

It looks round. This is because interphase cells are attached to the basement through a microtubule network. However in mitosis, this network depolymerizes to form the mitotic spindles. Therefore, the cell is poorly attached during mitosis and appears round

Front 4

How long is the average cell cycle? What percentage of time is mitosis in the cell cycle?

Back 4

The average cell cycle is about 20 hours. Mitosis takes up 2-3% of this time

Front 5

What test can you do to determine if cells are synthesizing DNA?

Back 5

You can add tritiated thymidiine (3H-TdR) to the cells. This is a radioactive thymidine, a DNA base. It is only incorporated to DNA, nowhere else in the cell. Therefore, if the cell is in in the synthesis phase, it will have radioactive fluorescence, because it took up the 3H-TdR

Front 6

What does colchicine do?

Back 6

It prevents MT polymerization, which prevents the mitotic spindles from forming. This arrests the cell in the beginning of mitosis

Front 7

How were the G1, S, G2, and M phases and their order discovered?

Back 7

Scientists used experiments with tritiated thimidine and colchicine. They found that over a time interval, no DNA was being synthesized, then it was synthesized, then it stopped being synthesized. These represented the G1, S, and G2 phase respectively

Front 8

How does a flow microflourimeter work?

Back 8

You set up a device that drops cells one at a time. You measure the flouresence of every cell that drops down, which represents how much DNA is in it (because you added a fluorescent dye that binds DNA)

Front 9

What are the relative amounts of DNA in a cell in G1 vs G2? What about S? How was this discovered?

Back 9

There is twice as much DNA in G2 as G1. S is somewhere in between. This was discovered using flow microfluorimetry

Front 10

What is the name of the factor that cause G0 cells to reenter the cell cycle?

Back 10

Mitogens

Front 11

At what point are the extra histone proteins transcribed to accomodate the extra DNA?

Back 11

Only the S phase. This was discovered using a cDNA probe for histone mRNA

Front 12

At what point in the cell cycle are histones phosphorylated?

Back 12

There is a great deal of histone phosphorylation in late G2, which is preceded by gradually increasing levels up from late G1

Front 13

What phase do you need to pass to go from G1 to S?

Back 13

The restriction point

Front 14

How does the double thymidine block work? After they have been blocked, how long do you wait?

Back 14

First add a DNA synthesis inhibitor, so some many cells get stuck at the beginning of S and some in the middle of S. Then remove the inhibitor, wait for S to complete. Now there should be no cells in the S phase. Re add the inhibitor, so that all cells will stop at the beginning of S phase. Now all of your cells will be at the same point in the cell cycle.

Front 15

Can an S phase nucleus induce S phase in a G1 nucleus? G2 nucleus? Can an M phase nucleus induce M phase in other nuclei?

Back 15

Yes, an S phase nucleus can induce S in a G1 nucleus but not in a G2 (it won't replicate twice). An M phase can cause chromosome condensation (beginning of M) in any nucleus

Front 16

What are the three checkpoints in the cell cycle? What is checked at each stage?

Back 16

The G1 / S checkpoint: Is the environment favorable for DNA replication?
The S checkpoint: Is the DNA damaged? Can it be repaired?
The G2 / M checkpoint: Is all the DNA replicated? Is the environment favorable for mitosis?