gene expression and cancer Flashcards
what is cancer?
a group of diseases caused by damage to genes that regulate mitosis and the cell cycle leading to unrestrained growth of cells. Consequently, a group of abnormal cells, a tumour, develops and constantly expands in size
not all tumours are cancerous, those that are cancerous are called
malignant
tumours that are not cancerous are called
benign
what are some key differences between malignant and benign tumours?
- benign grow very slowly whereas malignant grow rapidly
- cell nucleus of benign has a relatively normal appearance whereas the cell nucleus of malignant often appear darker and larger due to an abundance of DNA
- benign tumour cells produce adhesion molecules that makes them stick together and so they remain in tissue from which they arise= PRIMARY TUMOURS whereas malignant tumour cells do not produce adhesion molecules so they spread to other regions of the body, a process called metastasis= SECONDARY TUMOURS
- benign tend to have localised effects on the body whereas malignant often have whole-body effects like weight loss and fatigue
- benign can usually be removed by surgery alone whereas malignant removal usually involves radio and or chemotherapy along with surgery
in general, cancer cells are derived from a single mutant cell- explain how
- the initial mutation causes uncontrolled mitosis in this cell
- later, a further mutation in one of the descendant cells leads to other changes that causes subsequent cells to be different from normal in growth and appearance
what are the 2 main types of gene that play a role in cancer?
- oncogenes
- tumour suppressor genes
what are oncogenes?
mutations of proto oncogenes
what is the role of proto oncogenes?
stimulate a cell to divide when growth factors attach to a protein receptor on its cell-surface membrane
- this then activates genes that cause DNA to replicate and cell to divide
if a proto oncogene mutates into an oncogene genes that cause DNA to be replicated can be permanently activated (switched on) for 2 reasons:
1- the receptor protein on the cell-surface membrane can be permanently activated so cell division is switched on in even in the absence of growth factors
2- the oncogene may code for a growth factor that is then produced in excessive amounts, again stimulating excessive cell division
result is that cells divide too rapidly and out of control= a tumour, or cancer develops
a few cancers are caused by inherited mutations of proto-oncogenes that cause the oncogene to be activated but most cancer-causing mutations oncogenes are
acquired not inherited
explian how a proto oncogene’s role in cell division is like the accelerator pedal of a car
- it simply controls how fast it goes
- when it mutates into an oncogene it is as if the accelerator pedal has become stuck down and so cell division occurs at a very rapid and uncontrolled rate
what is the role of tumour suppressor genes?
slow down cell division, repair mistakes in DNA and ‘tell’ cells when to die- apoptosis (programmed cell death) so therefore have the opposite role to oncogenes
what happens if a tumour suppressor gene become mutated?
- it is inactivated (switched off)
- as a result, it stops inhibiting cell division and cells can grow out of control
- the mutated cells formed are usually structurally and functionally different from normal cells
- while most of these die, those that survive can make clones of themselves and form tumours
give an example of a tumour suppressor gene
BRAC1
what’s an important difference between oncogenes and tumour suppressor genes?
- oncogenes can cause cancer as a consequence of activation of proto oncogenes
- tumour suppressor genes cause cancer when inactivated
