Cell Signalling and Cancer Flashcards
In multicellular animals, cell division is controlled mainly by …
… extracellular signals
Necrosis
- Unplanned death
- Usually occurs in response to damage or infection
- Can cause further damage to surrounding cells and tissues.
M phase
- Mitosis - division of the nucleus
- Cytokinesis - cell splits in two
G1 phase
- Gap phase
- Cell continues to grow
- Monitors internal state and external environment
- Prepares for S phase.
S phase
- Synthesis
- The cell replicates its DNA
G2 phase
- Gap phase
- Cell continues to grow
- Monitors internal state and external environment
- Prepares for Mitosis.
Interphase
- Contains G and S phases
- Provides time for cell to enlarge and duplicate its cytoplasmic organelles.
Cell-cycle control system
- 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.
Why is the start transistion in late G1 phase especially important?
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.
Cyclin-depemdant protein kinases
- 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
Cyclins
- 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.
Cell cycle withdrawal
Many cells at some point will exit the cell cycle and undergo apoptosis (planned cell death) or enter a modified state called G0.
Quiescent cells
Have withdrawn to G0 but can re-enter the cell cycle under certain conditions e.g., presence of growth factors, cytokines, hormones or chemical agents.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.
Terminal differentiation
Permanent withdrawal from the cell cycle. Though also in a G0 state.
Includes neurones, keratinocytes and goblet cells.
Senescence
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.
Cancer cells avoid senescence arnd are said to be…
…immortalised or transformed
What leads to cancerous growth?
Persistent mis-regulation of cell division and survival due to mutations in genes that normally regulate these processes.
Benign tumour
Excessive growth of cells within their original tissue. Typically, less dangerous but can lead to a malignant tumour.
Malignant tumour
A tumour that is cancerous and its cells have to ability to invade surrounding tissue.
Metastases
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.
Cancer critical genes
Ones that can contribute to the development of cancer if they mutate
* Proto-oncogenes
* Tumour supressor genes
Proto-oncogenes
- 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.
Tmour Suppressor Genes
- 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.
