Cancer

Question 1

Explain the need to regulate the mitotic cell cycle tightly

Answer 1

1. The mitotic cell cycle is tightly regulated as it is important for normal cell division and development
2. Mitotic cell cycle is controlled by 3 checkpoints - G1, G2 and M checkpoint, which determines whether the cell cycle can proceed
3. This is to ensure that key processes such as DNA replication is accurate before cells move on to the next stage
4. This prevents dysregulation of checkpoints of cell division, prevent excessive cell cycle progression and uncontrolled cell division which would lead to tumour formation and eventually cancer

Question 2

State environmental causes of cancer

Answer 2

1. Chemical carcinogens such as tar in cigarettes
2. Ionising radiation such as ultraviolet light

Question 3

Outline the role of oncogenes (ras gene) in the development of cancer

Answer 3

1. Proto-oncogenes are genes that codes for proteins involved in regulation of normal cell growth and proliferation
2. Gain of function mutation in 1 copy of proto-oncogene leads to an increase in amount of proto-oncogene protein
3. Translocation of proto-oncogene results in proto-oncogene being situated under the control of an enhancer, increasing rate of transcription, producing excessive proto-oncogene protein, leading to excessive cell proliferation
4. Point mutation within a proto-oncogene results in a hyperactive proto-oncogene protein, leading to excessive cell proliferation
5. Rate of cell divison is greater than rate of cell death, resulting in uncontrolled cell division and tumour formation

Question 4

Outline the role of tumour suppressor genes (p53 gene) in the development of cancer

Answer 4

1. Tumour suppressor genes are genes that codes for proteins involved in inhibiting cell division and helps to prevent uncontrolled cell growth and proliferation
2. Loss of function mutation in both copies of tumour suppressor genes results in no functional protein produced
3. Cells with damaged DNA are unable to arrest cell cycle to allow time for damaged DNA to be repaired
4. Cells with damaged DNA are unable to carry out repair on its damaged DNA
5. Cells with damaged DNA are unable to initiate apoptosis even when DNA damage is beyond repair
6. Hence, cells with damaged DNA proceed through the cell cycle and continues to accumulate mutations, leading to uncontrolled cell division and eventually cancer

Question 5

Describe the development of cancer

Answer 5

1. Development of cancer is a multi-step process which requires the accumulation of mutations, angiogenesis and metastasis\
2. Chemical carcinogens such as tar in cigarettes can cause mutation such as base pair substitutions (not exhaustive, based on stimulus) in the genes controlling checkpoints of the cell cycle
3. Gain of function mutation in 1 copy of proto-oncogene results in hyperactive protein products, leading to excessive cell proliferation
4. Loss of function mutation in both copies of tumour suppressor genes results in non-functional protein, disrupting ability of the cell to initiate apoptosis. Hence, cell cycle is not inhibited, leading to excessive cell proliferation
5. Mutation in genes involved in apoptosis allows cells to evade programmed cell death even when DNA damage is beyond repair
6. Activation of genes coding for telomerase prevents progressive shortening of telomeres with each round of DNA replication, thus cancer cells to divide indefinitely
7. These mutations in a single somatic cell causes rate of cell division to be greater than rate of cell death, resulting in uncontrolled cell division and tumour formation
8. Angiogenesis, the growth of new blood vessels occurs within the tumour, to transport oxygen and nutrients to support the growth of the tumour
9. When tumour cells invade surrounding tissues and metastasise, tumour is said to be malignant and cancer has developed

Question 6

Describe how dysregulation of the checkpoints of cell division may lead to cancer.

Answer 6

1. G1, G2 and M checkpoint determines whether or not the cell cycle can proceeed
2. When dysregulation of checkpoints of cell division occurs, there will be an excessive cell cycle progression and uncontrolled cell division, leading to tumour formation and eventually cancer