Topic 8—A: Mutations and Gene expression- 3. Cancer Flashcards
If a mutation occurs in a gene that controls cell division what can it cause?
Cancer
Why can it cause cancer?
- the genes that control cell division don’t behave as they should which can result in uncontrolled cell growth
Definition of acquired mutations
- Mutations that occur in individual cells after fertilisation (e.g. in adulthood)
If acquired mutations occur in the genes the control the rate of cell division (by mitosis) what can it cause?
- uncontrolled cell division
What is the result if a cell divides uncontrollably ?
Tumour
Definition of tumour
- a mass of abnormal cells
Cancers
- tumours that invade and destroy surrounding tissue are called cancers
What are the two types of gene that control cell division?
- tumour suppressor genes
- proto-oncogenes
What will mutations in these genes cause?
Cancer
Tumour suppressor genes
- when functioning normally, tumour suppressor genes slow cell division by producing proteins that stops cell dividing or cause them to self destruct (apoptosis)
What happens if a mutation occurs in a tumour suppressor genes ?
- the gene will be inactivated
- the protein it codes for isn’t produced
- cells divide uncontrollably
- resulting in a tumour
Proto-oncogenes
- when functioning normally, proto oncogenes stimulate cell division by producing proteins that make the cells divide
What happens if a mutation occurs in a proto-oncogene?
- the gene can become overactive
- this stimulates the cells to divide uncontrollably
- resulting in a tumour
What is a mutated proto-oncogene called?
An oncogene
What are the two different types of tumours?
- Malignant tumours
- Benign tumours
What are malignant tumours?
- they are cancers
- they usually grow rapidly
- they invade and destroy surrounding tissues
- cells can break off the tumours and spread to other parts of the body in the bloodstream or lymphatic system
What are benign tumours?
- not cancerous
- usually grow slower
- often covered in fibrous tissue that stops cells invading other tissues
- often harmless
- can cause blockages and put pressure on organs
- they can become malignant
Tumour cells (differences to normal cells)
- the nucleus is larger and darker than in normal cells
- sometimes the cells have more than 1 nucleus
- they have an irregular shape
- they don’t produce all the proteins needed to function correctly
- they have different antigens on their surface
- they don’t respond to growth regulating processes
- they divide by mitosis more frequently than normal cells
What are the causes of tumour growth?
- abnormal methylation of DNA
- Increased exposure to oestrogen
Abnormal methylation
- methylation means adding a methyl (-CH3) group onto something
- methylation of DNA is an important method of regulating gene expression- it can control whether or not a gene is transcribed (copied into mRNA) and translated (turned into a protein)
- When methylation is happening normally, it plays a key role in many processes in the body
- it’s only when it happens too much (hyper methylation) or too little (hypo methylation) that it becomes a problem
- the growth of tumours can be caused by abnormal methylation of certain cancer related genes
Examples: abnormal methylation
- when tumour suppressor genes are hyoermethylated the genes are not transcribed- the proteins they produce to slow cell diviosn aren’t made
- this means that cells are balke to divide uncontrollably by mitosis and tumours can develop
- hypomethylation of proto-oncogenes causes them to act as oncogenes
- this increases the production of the proteins that encourage cell division
- this stimulates cells to drive uncontrollably which causes the formation of tumours
Role of oestrogen in breast cancer
- increased exposure to oestrogen over an extended period of time is thought to increase a women’s risk of developing breast cancer
- oestrogen can stimulate certain breast cells to divide and replicate. More cell divisions are taking place naturally increases the chance of mutations occurring and so increases the chance of cells becoming cancerous
- oestrogens ability to stimulate cell division could also mean that if cells do become cancerous, their rapid replication could be further assisted by oestrogen, helping tumours to form quickly
- oestrogen is able to introduce mutations directly into the DNA of certain breast cells, increasing the chance of these cells becoming cancerous
