Case 4- cell cycle

Question 1

What is the cell cycle

Answer 1

The time between two cell divisions

Question 2

Cell cycle- G1

Answer 2

Growth stage, increase in size

Question 3

Cell cycle- G0

Answer 3

Resting stage, dormant stage which cells enter to exit the cell cycle. If they want to re-enter the cell cycle they enter at G1

Question 4

Cell cycle- S

Answer 4

DNA is replicated to produce another copy. Takes about 12 hours. All genetic material is replicated. The two sister chromatids are held together by a centromere

Question 5

Cell cycle- G2

Answer 5

Another growth stage, increase in size and prepares for mitosis. Can vary in length depending on cell type

Question 6

Cell cycle- M

Answer 6

Division of cell to produce two new cells. Involves mitosis and cytokinesis. In mitosis the chromosomes are separated between the two new cells and in cytokinesis the cytoplasm splits to produce two new cells. Nuclear envelope and cell mebrane are reformed

Question 7

Sequence of mitosis

Answer 7

Prophase, metaphase, anaphase, Telophase

Question 8

Prophase

Answer 8

The chromosomes condense to become more compact, so they are easier to separate, in late prophase the mitotic spindle is formed

Question 9

Metaphase

Answer 9

In protometaphase the chromosomes organise themselves within the cell, chromosomes attach to spindle. The nuclear membrane breaks down. In metaphase the chromosomes line up along the equator of the cell.

Question 10

Anaphase

Answer 10

The chromosomes are pulled apart so one full copy of the chromosome move to each pole of the cell, this is done by the mitotic spindle

Question 11

Telophase

Answer 11

The nuclear membrane begins to reform around each set of chromosomes

Question 12

The checkpoints in the cell cycle

Answer 12

1) The restriction point between G1 and S
2) The S-phase checkpoint
3) The checkpoint between G2 and M
4) The checkpoint in the metaphase to Anaphase transition

Question 13

Checkpoints in the cell cycle- The restriction point between G1 and S

Answer 13

Is the environment favourable, is there a growth stimulatory pathway. Is there enough growth stimulation for the cell to divide? Is the DNA good for replication?

Question 14

Checkpoints in the cell cycle- The S-phase checkpoint

Answer 14

Checks that DNA synthesis has happened correctly, there should be a full complete copy.

Question 15

Checkpoints in the cell cycle-The checkpoint between G2 and M

Answer 15

Checks that the DNA has replicated correctly and that the environment is favourable. Is there still a growth stimulatory signal?

Question 16

Checkpoints in the cell cycle- the checkpoint in the Metaphase to Anaphase transition

Answer 16

Checks that the chromosomes can correctly separate to each end of the cell. Anaphase bridges can occur where the chromosomes remain attached together, eventually this will snap but it may not allow for one full set of chromosomes to go to each end of the cell. May snap unevenly which will affect cell division which could lead to cancer. Has the mitotic spindle correctly attached to the chromosomes and are the chromosomes aligned?

Question 17

What happens if an error is detected at a checkpoint?

Answer 17

The cell cycle can be blocked to stop the errors from being passed to other cell to avoid uncontrolled cell division

Question 18

How does the cell control movement through the checkpoints

Answer 18

Through enzymes, specifically cyclin dependent kinases (Cdks). Cyclin-Cdk complexes trigger events in the cell cycle by phosphorylating specific target proteins. This drives the cell through the checkpoints.

Question 19

Enzymes in G1

Answer 19

Cyclin D binds to CDK4 and CDK6 which push the cell through its cycle.

Question 20

Enzymes at the end of G1

Answer 20

Cyclin E activates CDK2 to drive it through the checkpoint.

Question 21

Enzymes at the end of S phase

Answer 21

Cyclin A activates CDK2 to get to the G2 stage.

Question 22

Enzymes in G2

Answer 22

Cyclin A binds to CDK1.

Question 23

Enzymes at the end of G2

Answer 23

Cyclin B binds/activates CDK1 to get through that checkpoint and for mitosis to occur. So, the right cyclin needs to be present at the right point.

Question 24

To stimulate the cell cycle

Answer 24

1) A mitogen (growth factor) binds to a receptor.
2) Once the receptor has been activated the signal is sent down the cell by activating Ras GTPase (transducer).
3) This induces a signalling cascade which activates MAP kinase.
4) The signal arrives at the nucleus and there is an increase in Myc transcription (transcription factor). This transcription factor cause transcription of the G1 cyclins, the increase in cyclins causes the CDKs to be activated.
5) The cell then progresses through the cell cycle. Many genes in this pathway are linked to cancer (oncogenes).

Question 25

To inhibit the cell cycle

Answer 25

When something has gone wrong. There are a series of proteins that inhibit the cyclin-CDK complex. The inhibitors are the INK4 family and the Cip/Kip family.

Question 26

Cell cycle- P53

Answer 26

An important gene in the suppression of the cell cycle and stops it dividing in an uncontrolled way, is a tumour suppressor. It indirectly inactivates G1/s-Cdks and S-Cdks. In also plays a role in programmed cell death (apoptosis). It activates p21 which inhibits the cell cycle to check what the mistake is and if repair is possible, if it cannot be repaired apoptosis occurs. A mutation on this gene is common in cancer, results in half of all cancers. It’s a target for viral oncoproteins which can cause cancer by inhibiting its activity. Target of many anti-cancer drugs. P53 will be active due to excess mitogenic pressure, errors in mitosis, DNA damage, oncogene activation and cell stress.

Question 27

How mistakes in telomeres can lead to cancer

Answer 27

The telomere gets shorter after each cell division. If the cell continues to divide after the telomere becomes very short, then vital genes will be lost. In some cancer cells they divide when the telomere is too short, they divide indefinitely, and genes get lost.

Question 28

How mistakes in KRas can lead to cancer

Answer 28

You lose cell cycle control in cancer by overactivation of the genes that stimulate cell division. E.g. KRas which activates the RAS/MAPK pathway, KRas is an oncogene. Another way to lose control is through inactivation of the gene that inhibits cell division i.e. p53 which is a tumour suppressor gene. Cancer cells will have multiple mutations

Question 29

What causes cancer

Answer 29

If the cell cycle goes wrong you will get cells that divide more rapidly then normal and this can lead to tumour formation. Cancer is driven by genetic alterations (mutations in DNA or epigenetic changes). These alterations can be due to a DNA damaging stimulant or a spontaneous DNA replication error. This cell will collect mutations as it divides till it has enough mutations to divide in a completely uncontrolled way. A cellular mass forms which develop into a tumour. The cancer cell can no longer perform its function

Question 30

How do cancer cells affect adjacent cells

Answer 30

They interfere with adjacent cellular function at the originating site by creating a necrotic environment. Can also be when the tumour compresses neighbouring organs or structures. They can also completely colonise that area of the body, meaning more of the organ loses function.

Question 31

What features do cancer cells have

Answer 31

Abnormal cellular morphology, increased rate of mitosis, multi-nucleated cells, increased nuclear DNA and disorganised tissue architecture.

Question 32

Oncogene

Answer 32

Genes involved in cell division e.g B-raf kinase

Question 33

Tumour suppressor gene

Answer 33

Genes involved in preventing cell division

Question 34

Cancer- transformation

Answer 34

The process by which a cell becomes cancerous

Question 35

Cancer- clonality

Answer 35

Being genetically identical

Question 36

Carcinogen

Answer 36

A substance which promotes genetic mutations and cancer formation

Question 37

Cellular oncogene

Answer 37

When structures within the cell cause mutations

Question 38

Viral oncogene

Answer 38

When a virus causes a mutation

Question 39

Proto- oncogene

Answer 39

The original form of a cell before it becomes cancerous