Cell Signalling and Cancer

Question 1

In multicellular animals, cell division is controlled mainly by …

Answer 1

… extracellular signals

Question 2

Necrosis

Answer 2

• Unplanned death
• Usually occurs in response to damage or infection
• Can cause further damage to surrounding cells and tissues.

Question 3

M phase

Answer 3

• Mitosis - division of the nucleus
• Cytokinesis - cell splits in two

Question 4

G1 phase

Answer 4

• Gap phase
• Cell continues to grow
• Monitors internal state and external environment
• Prepares for S phase.

Question 5

S phase

Answer 5

• Synthesis
• The cell replicates its DNA

Question 6

G2 phase

Answer 6

• Gap phase
• Cell continues to grow
• Monitors internal state and external environment
• Prepares for Mitosis.

Question 7

Interphase

Answer 7

• Contains G and S phases
• Provides time for cell to enlarge and duplicate its cytoplasmic organelles.

Question 8

Cell-cycle control system

Answer 8

• Made up of several regulatory proteins
• Ensures that the events of the cell cycle occur correctly.
• This is achieved via checkpoints which act as brakes.

Question 9

Why is the start transistion in late G1 phase especially important?

Answer 9

Because at that point the system is regulated by outside signals – which block or stimulate cell-proliferation. This means that it plays a large role in the regulation of the number of cells in tissues. If the control system malfunctions it can lead to the excessive division of cells and to cancer.

Question 10

Cyclin-depemdant protein kinases

Answer 10

• Concentration does not change throughout cell cycle.
• Activity rises and falls cyclically
• Must bind cyclins to be activated.
• Once activated, the complex phosphorylated important proteins in the cell

Question 11

Cyclins

Answer 11

• Are bound by cyclin dependent kinases
• Unlike Cdks the concentration changes cyclically throughout the cell cycle
• Changes in concentration drive the cyclic assembly and activation of cylin-Cdk complexes
• The rise in cyclins is due to the transcription of cyclin genes and formation of cyclin proteins.
• Degraded at various points during the cycle, which can drive entry into the next phase.

Question 12

Cell cycle withdrawal

Answer 12

Many cells at some point will exit the cell cycle and undergo apoptosis (planned cell death) or enter a modified state called G0.

Question 13

Quiescent cells

Answer 13

Have withdrawn to G0 but can re-enter the cell cycle under certain conditions e.g., presence of growth factors, cytokines, hormones or chemical agents.
Liver cells are an example.

Question 14

Terminal differentiation

Answer 14

Permanent withdrawal from the cell cycle. Though also in a G0 state.
Includes neurones, keratinocytes and goblet cells.

Question 15

Senescence

Answer 15

The termination of cell division.
For most normal cells, they have a limit on the number of times they can divide. Stem cells are an exception.

Question 16

Cancer cells avoid senescence arnd are said to be…

Answer 16

…immortalised or transformed

Question 17

What leads to cancerous growth?

Answer 17

Persistent mis-regulation of cell division and survival due to mutations in genes that normally regulate these processes.

Question 18

Benign tumour

Answer 18

Excessive growth of cells within their original tissue. Typically, less dangerous but can lead to a malignant tumour.

Question 19

Malignant tumour

Answer 19

A tumour that is cancerous and its cells have to ability to invade surrounding tissue.

Question 20

Metastases

Answer 20

Cells that break through boundaries and enter the bloodstream and take over distant sites in the body are said to form metastases, which can be highly dangerous.

Question 21

Cancer critical genes

Answer 21

Ones that can contribute to the development of cancer if they mutate
* Proto-oncogenes
* Tumour supressor genes

Question 22

Proto-oncogenes

Answer 22

• Normally encode for proteins that lead to cell division.
• Mutations that lead to a gain-of-function can convert them into overactive (onco-genes).
• The activation of these leads to the overexpression of cell-growth proteins and in uncontrolled cell-proliferation and tumours.
• These mutations are usually dominant and sometimes only one is required to activate the onco-gene, for example: Ras signalling cascades.

Question 23

Tmour Suppressor Genes

Answer 23

• Generally, encode proteins that inhibit cell proliferation and trigger apoptosis.
• If they have a loss-of-function mutation in the may cause the uncontrolled proliferation of a cell
• The mutations are recessive, so they must be present on both alleles.