Cancer

Question 1

Causative factors that increases chances of cancer

Answer 1

• environmental factors
  –> exposed to carcinogens. (e.g. tar in cigarette smoke) and ionising radiation (e.g. uv radiation, X-rays) can cause mutations that can lead to cancer
• loss of immunity due to infection with certain viruses
  –> HIV can weaken the immune system and reduces the body’s ability to. fight infections by other viruses that can cause cancer
• genetic predisposition –> due to gene mutations which we inherit from our parents
• age –> chances of cancer increases with age due to accumulation of mutations in a cell over a lifetime

Question 2

Proto-oncogenes

Answer 2

• code for proteins that stimulate cell division/proliferation
• when mutated, they become oncogenes
  1. increase the amount of proto-oncogene’s protein product
• point mutation in base sequences of regulatory elements, increased frequency of transcription and excess production of proto-oncogene protein product can lead to uncontrolled cell division
• gene amplification where the number of copies of proto-oncogene in a cell is increased due to a mistake made during DNA replication, excessive production of proto-oncogene product –> uncontrolled cell division
• chromosomal translocation such that proto-oncogene ends up under the control of an enhancer
• retroviral integration –> inactivate a silencer of a proto-oncogene, result in insertion of a viral enhancer that upregulates expression of proto-oncogene, can insert a viral homologue of proto-oncogene

2. increase in intrinsic activity of proto-oncogene protein product
   –> by a point mutation within the proto-oncogene, changes amino acid sequence of the proto-oncogene protein, which become more hyperactive or more resistant to degradation leads to uncontrolled cell division

Question 3

tumour suppressor genes

Answer 3

• codes for protein product that inhibit. cell division and prevent uncontrolled cell division by upregulating the expression of genes involved in cell cycle arrest, DNA repair and apoptosis
• when mutated, they are inactivated, mutations could be in promoter or coding sequence of gene

Question 4

Why is development of cancer a multi-step process?

Answer 4

• the development of cancer requires the accumulation of mutations in the genes which control regulatory checkpoints of the cell in a single cell
• this will disrupt normal cell cycle, causing excessive cell proliferation
• gain-in-function of the proto-oncogene is a dominant mutation where mutation in just one allele will result in its overexpression which will produce excessive amounts of growth factors or hyperactive resistant. growth factors leading to excessive cell proliferation
• loss-in-function mutation of tumour suppressor genes is a recessive mutation where mutations in both alleles will result in non-functional protein which will disrupt the ability to inhibit cell cycle, trigger apoptosis and enable DNA repair
• activation of the genes coding for telomerase result in telomeres being lengthened, allowing the cell to divide indefinitely as chromosomes are prevented from shortening with each DNA replication cycle
• loss of contact inhibition will enable the cells to grow into a benign tumour
• angiogenesis occur within the tumour so that blood vessels can transport oxygen and nutrients for its growth
• presence of blood vessels. can result in formation of malignant tumour capable of metastasizing to other parts of the body via the bloodstream to form secondary tumours