Biology · JC 1 · Biological Systems and the Environment · Semester 2

Cancer Biology: Oncogenes, Tumour Suppressors, and Multistep Carcinogenesis

Students will investigate the causes of climate change, focusing on the greenhouse effect and human activities, and its biological impacts.

• MOE Syllabus Outcomes
• MOE: Climate Change - MS

About This Topic

Cancer biology examines how genetic mutations drive uncontrolled cell growth. Students learn that proto-oncogenes become oncogenes through gain-of-function mutations, which hyperactivate signalling pathways for proliferation. Tumour suppressor genes, such as TP53, normally halt the cell cycle at checkpoints; loss-of-function mutations require both alleles to be inactivated per the two-hit hypothesis, explaining their recessive nature at the cellular level. These concepts connect to cell division topics from earlier units.

The topic extends to cancer hallmarks: sustained proliferative signalling, evasion of growth suppressors and apoptosis, replicative immortality, angiogenesis induction, and activation of invasion plus metastasis. Students analyse these as outcomes of cumulative somatic mutations. The clonal selection model illustrates tumour progression, where cells with advantageous mutations outcompete others, leading to increasingly malignant clones through natural selection.

This content suits active learning because abstract mutation accumulation and selection processes gain clarity through simulations and collaborative modelling. Students manipulate variables in games or diagrams, debate hallmark vulnerabilities, and track 'tumour' evolution in groups, making multistep carcinogenesis concrete and fostering critical evaluation of therapeutic targets.

Key Questions

1. Explain how gain-of-function mutations in proto-oncogenes and loss-of-function mutations in tumour suppressor genes disrupt normal cell cycle control, applying the two-hit hypothesis to explain the recessive nature of tumour suppressor loss at the cellular level.
2. Analyse the hallmarks of cancer , sustained proliferative signalling, evasion of apoptosis, induction of angiogenesis, and activation of invasion and metastasis , as consequences of cumulative somatic mutations, evaluating how each hallmark represents a targetable vulnerability.
3. Evaluate the clonal selection model of tumour progression, explaining how successive rounds of mutation and natural selection within a growing tumour drive the stepwise acquisition of increasingly malignant phenotypes.

Learning Objectives

• Explain the molecular mechanisms by which proto-oncogene mutations lead to sustained proliferative signalling.
• Analyze how loss-of-function mutations in tumour suppressor genes, following the two-hit hypothesis, result in uncontrolled cell division.
• Evaluate the multistep nature of carcinogenesis by describing how cumulative somatic mutations drive the acquisition of cancer hallmarks.
• Critique the clonal selection model as a framework for understanding tumour progression and the development of malignancy.

Before You Start

Cell Cycle Regulation

Why: Understanding the normal checkpoints and regulatory proteins of the cell cycle is essential for comprehending how mutations disrupt this process.

Principles of Genetics: Gene Expression and Mutation

Why: Students need foundational knowledge of genes, alleles, mutations (point mutations, deletions), and gene function to grasp the impact of genetic changes on cell behaviour.

Key Vocabulary

Proto-oncogene	A normal gene that, when mutated or altered, can contribute to cancer development by promoting uncontrolled cell growth.
Oncogene	A gene that has the potential to cause cancer. It is typically a mutated or activated proto-oncogene.
Tumour suppressor gene	A gene that protects a cell from becoming cancerous. Its inactivation, often through mutation, can lead to cancer.
Two-hit hypothesis	The concept that two mutations, one in each copy of a tumour suppressor gene, are typically required for cancer to develop at the cellular level.
Hallmarks of cancer	A set of biological capabilities acquired during the multistep development of human cancer, such as sustained proliferative signalling and evasion of apoptosis.

Watch Out for These Misconceptions

Common Misconception

Cancer arises from a single mutation.

What to Teach Instead

Tumours require multiple mutations over time, as per multistep carcinogenesis. Timeline activities where groups add mutations sequentially help students visualize accumulation and connect to clonal selection, correcting the idea of instant transformation.

Common Misconception

Tumour suppressor mutations are dominant like oncogenes.

What to Teach Instead

Suppressors act recessively, needing two hits; oncogenes are dominant with one hit. Simulations with paired alleles demonstrate this, as students see single suppressor hits still permit control, building accurate mental models through hands-on comparison.

Common Misconception

All cancer cells are equally aggressive from the start.

What to Teach Instead

Clonal evolution selects for aggressive traits stepwise. Group competitions modelling selection pressures reveal heterogeneity, helping students grasp why tumours progress variably and why early intervention matters.

Active Learning Ideas

Card Game: Mutation Accumulation

Provide cards representing proto-oncogene activations, tumour suppressor losses, and environmental mutagens. In small groups, students draw cards over rounds to simulate cell lineages, scoring points for acquiring hallmarks like apoptosis evasion. Discuss final 'tumour' profiles and clonal dominance.

45 min·Small Groups

Model Building: Two-Hit Hypothesis

Pairs construct physical models using beads for alleles on chromosomes. Introduce 'hits' via dice rolls or pins to inactivate suppressors. Observe how single hits allow normal function but double hits trigger proliferation, linking to pedigree analysis.

30 min·Pairs

Case Study Rotation: Cancer Hallmarks

Set up stations for each hallmark with patient data excerpts. Small groups rotate, annotating mutations causing sustained signalling or angiogenesis. Regroup to present connections to multistep model.

50 min·Small Groups

Formal Debate: Clonal Selection Vulnerabilities

Divide class into teams representing tumour clones with specific mutations. Debate how therapies target early versus late hallmarks, using evidence from model tumours built earlier. Vote on most promising interventions.

40 min·Whole Class

Real-World Connections

• Oncologists and cancer researchers utilize knowledge of oncogenes and tumour suppressor genes to develop targeted therapies, like imatinib (Gleevec) for chronic myeloid leukemia, which inhibits the specific oncogenic protein BCR-ABL.
• Genetic counselors assess family histories for inherited predispositions to cancer, often linked to germline mutations in tumour suppressor genes like BRCA1 and BRCA2, advising individuals on screening and risk management strategies.

Assessment Ideas

Quick Check

Present students with a diagram showing a cell cycle checkpoint. Ask them to annotate the diagram, indicating where a gain-of-function mutation in a proto-oncogene or a loss-of-function mutation in a tumour suppressor gene would disrupt normal regulation.

Discussion Prompt

Facilitate a class debate: 'Is cancer primarily a disease of genetic instability or a process of evolutionary selection within the body?' Students should use the concepts of oncogenes, tumour suppressors, and the hallmarks of cancer to support their arguments.

Exit Ticket

Provide students with two scenarios: one describing a mutation in a proto-oncogene, the other in a tumour suppressor gene. Ask them to write one sentence explaining the immediate cellular consequence of each mutation and one sentence describing how this contributes to cancer development.

Frequently Asked Questions

How do oncogenes differ from tumour suppressors in cancer?

Oncogenes result from gain-of-function mutations in proto-oncogenes, like RAS, driving constant proliferation signals with one mutated allele. Tumour suppressors, such as RB or TP53, require loss-of-function in both alleles via the two-hit hypothesis to fail in restraining the cell cycle. Classroom models clarify this dominance versus recessivity, linking to hallmarks like proliferative signalling.

What is the two-hit hypothesis in tumour suppressors?

Proposed by Knudson, it states both alleles of a tumour suppressor must be inactivated for cancer: one inherited germline hit, one somatic. This explains retinoblastoma patterns. Students apply it to evaluate why sporadic cancers need multiple events, using allele-tracking exercises to predict risks and reinforce cellular recessivity.

How does active learning benefit teaching cancer biology?

Active strategies like mutation simulation games and hallmark case studies make invisible genetic processes tangible. Students in groups track clonal evolution, debate therapies, and build allele models, deepening understanding of multistep progression. This shifts passive recall to critical analysis, improving retention of complex ideas like selection pressures and targetable vulnerabilities in JC1 Biology.

What are the key hallmarks of cancer relevant to JC1?

Hallmarks include sustained proliferative signalling, evading apoptosis and growth suppression, inducing angiogenesis, and activating invasion plus metastasis. Students evaluate these as mutation consequences, seeing them as therapy targets. Clonal selection ties them to progression, with activities like station rotations helping connect abstract traits to real tumour dynamics.