gene expression and cancer Flashcards
Cell Division [4]
Cell division is tightly controlled by genes, there are two types involved in this:
- Tumour suppressor genes inhibit cell division
- Proto-oncogenes stimulate cell division
A balance between the expression of these genes ensure that cells divide at a fairly constant rate, and those cells that are worn out or dead are replaced.
Characteristics of Malignant tumours [9]
- Grow rapidly
- Grow to a large size
- Larger & darker nucleus (due to abundant DNA)
- Removal often requires radiotherapy/chemotherapy
- Frequently re-occur after treatment
- Increased likelihood of being life-threatening as abnormal tumour tissue replaces normal tissues
- Tumours not surrounded by a capsule so grow finger-like projections into surrounding tissues
- Systemic (whole body) effects e.g. weight loss, fatigue
- Cells de-differentiate (unspecialised)
Characteristics of Benign tumours [10]
- Grow slowly
- Grow to a small size
- Normal appearance of nucleus
- Can be removed by surgery alone
- Rarely re-occur after treatment
- Can disrupt functioning on an organ but less likely to be life-threatening
- Tumours surrounded by capsule of dense tissue & have a compact structure
- Adhesion molecules produced and remain within the tissue from which they arose (primary tumours)
- Localised effects on the body
- Cells are well differentiated (specialised)
How do cancer cells form? [2]
- Cancer cells derive from a single mutated cell which causes uncontrolled mitosis
- Further mutations in a daughter cell leads to changes in growth & appearance of other daughter cells
Metastasis [4]
- Metastasis is when a tumour spreads
- Cancerous cells leave the primary tumour, by squeezing into blood or lymph vessels
- They circulate in the blood until they lodge somewhere else in the body
- A secondary tumour will form here.
Proto-oncogenes [3]
- Growth factors are detected by protein receptors
on the cell surface membrane - These cause relay proteins in the cytoplasm to express the proto-oncogenes
- This is a normal process for cell replication.
Oncogenes [7]
- A mutation can cause proto-oncogenes to mutate into oncogenes
This is when these genes are permanently expressed: - The receptor on the cell surface membrane could be permanently activated
- A growth factor is produced in excessive amounts
- Cells divide too rapidly, and out of control
- Tumours (cancers) develop
- Cancers due to oncogenes tend to be caused by environmental factors rather than inherited
Oestrogen can cause proto-oncogenes in breast tissue to mutate to oncogenes
Tumour Suppressor Genes [5]
- These slow down cell division
- Repair mistakes in DNA
- Instructs apoptosis (programmed cell death)
- This maintains normal cell division and prevents tumours from developing
- If these genes become inactivated a tumour can develop
If a mutation occurs….. [3]
- Cells do not stop dividing
- They will be structurally & functionally different
- Most die but some survive and clone creating a tumour
How would epigenetic tags affect expression of oncogenes and tumour suppressor genes?
Abnormal methylation of tumour suppressor genes
If hypermethylation occurs in a promoter region of a tumour suppressor gene, what would happen? [3]
- Transcription of promoter region inhibited
- Tumour suppressor gene silenced
- Leads to increased cell division and tumour formation
Oestrogen Production
Oestrogen production from ovaries diminishes post menopause
BUT
It increases as fat cells in breast tissue start production
Effect of Oestrogen Concentration
- Once a tumour starts to develop, it increases oestrogen production therefore increasing the tumour production
- White blood cells are drawn to the tumour and also increase oestrogen concentration
How does oestrogen cause uncontrolled cell division?
- Oestrogen allows a transcription factor to be activated
- This transcription factor acts on a gene that controls cell division
- Continued stimulation of the gene causes uncontrolled cell division
- Tumour growth develops
