S1: Biology of Cancer

Question 1

What positive signals do cells receive telling it to divide?

Answer 1

Growth factors

Hormones

Question 2

What is growth factor ‘Epidermal growth factor (EGF)’?

Answer 2

Protein can bind to the cell membrane to its specific receptor (ECF receptor).
Upon binding it will cause signal transduction molecules (secondary messengers) and these will signal to the nucleus where they will cause changes in gene expression

Question 3

What signal do cells receive telling them not to divide?

Answer 3

-Contact Inhibition: When cell is surrounded by other cells, it receives signals from other cells telling it new cells aren’t needed so it shouldn’t divide

DNA damage response: If there is something wrong with DNA in the cell, the cell will not divide until that DNA is repaired

Question 4

What does germline mutation mean?

Answer 4

• Present in the fertilised egg
• Present in every cell in the body
• Can be inherited from a parent
• Can be passed to offspring

Question 5

What does somatic mutation mean?

Answer 5

• Occurs after division of the fertilised egg
• Only present in a subset of cells
• Not inherited from a parent
• Occasionally passed to offspring

Question 6

Why is cancer called ‘clonal disease’?

Answer 6

It arises from a single cell. This cell has undergone mutations and gene dysregulation so its cell division is no longer tightly controlled

Question 7

What type of mutations is cancer mostly caused by?

Answer 7

Somatic mutations - Mutations in a single cell rather than inherited mutations

Question 8

What are the genes that are mutated?

Answer 8

• Oncogenes

- Tumour suppressor genes

Question 9

What is dominant oncogenes?

Answer 9

With these, only one copy of the gene (one allele in a diploid cell) needs to be mutated

Question 10

Explain how tumour suppressor genes (TSGs) cause cancer

Answer 10

Tumour suppressor genes (TSGs) require both copies of the gene (both alleles, in a diploid cell) to be inactivated in order to allow cancer to develop.
Typical TSGs may be: cell cycle checkpoint genes, DNA repair genes or genes regulating cell death.

Question 11

How many mutations cause cancer?

Answer 11

Multiple mutations in different genes are what causes cancer. When one cell acquires enough mutations it begins to grow out of control.

Question 12

What are the types of cellular genes mutated in cancer?

Answer 12

• Growth promoting genes (which would be dominant oncogenes)
• Cell cycle checkpoint genes and DNA repair genes (which would be tumour suppressor genes)
• Genes regulating cell death (dominant oncogenes or tumour suppressor genes)

Question 13

How are oncogenes made?

Answer 13

Most oncogenes start out as normal cellular genes coding for a protein carrying out a normal cellular function. They only become an oncogene after genetic alteration. A “proto-oncogene” is a normal gene that can be mutated to become an oncogene.

Question 14

Example of an Oncogene

Answer 14

HER2 in some cases of breast cancer

Question 15

Example of tumour suppressor genes

Answer 15

TP53 gene codes for the p53 protein

Question 16

Explain how DNA repair genes can cause cancer

Answer 16

Many tumours lack proper DNA repair, due to the genes coding for DNA repair proteins being mutated. Hence other genes are more likely to mutate and the cell is more likely to become cancerous.
Mutations in DNA repair genes=Increased risk of mutations in oncogenes/tumour suppressor genes

Question 17

Give and example of a DNA repair gene

Answer 17

BRCA1

If mutated, individuals are more likely to get breast cancer

Question 18

How do tumour progress?

Answer 18

• To promote invasion and metastasis
• To become invisible to the immune system
• To induce growth of blood vessels

Question 19

Why is angiogenesis important for cancer?

Answer 19

Angiogenesis is the formation of blood vessels, for a tumour to grow it must have a blood supply. Cancer cells secrete angiogenic factors to induce new blood vessels. Anti-angiogenic drugs inhibit the growth of tumours.

Question 20

What is knudsons two hit hypothesis?

Answer 20

SPORADIC

• Single tumour
• Unilateral
• Late onset

HEREDITARY

• Multiple tumours
• Bilateral
• Early onset

Question 21

What is epigenetics?

Answer 21

Epigenetics is the study of changes in gene expression caused by mechanisms other than changes in the underlying DNA sequence.

Question 22

Give an example of epigenetic modification

Answer 22

DNA methylation

e.g. methylation of cytosine