Topic 8.2.3 Gene expression and cancer

Question 1

Describe how tumours and cancers form

Answer 1

● Mutations in DNA / genes controlling mitosis can lead to
uncontrolled cell division
● Tumour formed if this results in mass of abnormal cells
○ Malignant tumour = cancerous, can spread by metastasis
○ Benign tumour = non-cancerous

Question 2

Compare the main characteristics of benign and
malignant tumours

Answer 2

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Question 3

Describe the function of tumour suppressor genes

Answer 3

Code for proteins that:
● Inhibit / slow cell cycle (eg. if DNA damage detected)
● OR cause self-destruction (apoptosis) of potential
tumour cells (eg. if damaged DNA can’t be repaired)

Question 4

Explain the role of tumour suppressor genes in the development of tumours

Answer 4

● Mutation in DNA base sequence → production of non-functional protein
○ By leading to change in amino acid sequence which changes protein tertiary structure
● Decreased histone acetylation OR increased DNA methylation → prevents production of protein
○ By preventing binding of RNA polymerase to promoter region, inhibiting transcription
● Both lead to uncontrolled cell division (cell division cannot be slowed)

Question 5

Describe the function of (proto-)oncogenes

Answer 5

Code for proteins that stimulate cell division
(eg. through involvement in signalling pathways
that control cell responses to growth factors)

Question 6

Explain the role of oncogenes in the development of tumours

Answer 6

● Mutation in DNA base sequence → overproduction of protein OR permanently activated protein
○ By leading to change in amino acid sequence which changes protein tertiary structure
● Decreased DNA methylation OR increased histone acetylation → increases production of protein
○ By stimulating binding of RNA polymerase to promoter region, stimulating transcription
● Both lead to uncontrolled cell division (cell division is permanently stimulated)

Question 7

Suggest why tumours require mutations in both alleles of a tumour
suppressor gene but only one allele of an oncogene

Answer 7

● One functional allele of a tumour suppressor gene can produce enough protein to slow the cell cycle
OR cause self-destruction of potential tumour cells → cell division is controlled
● One mutated oncogene allele can produce enough protein to lead to rapid / uncontrolled cell division