Cancer Genetics chapter 3

Introduction to Cancer Genetics

  • Discussion on the genetic basis of cancer, focusing on coding genes and their roles in cancer development.

Tumor Suppressor Genes

  • Definition: Tumor suppressor genes are genes in our DNA that help to prevent the formation of tumors.

    • Their primary function is to control cell growth and division, ensuring that cells do not divide uncontrollably.

  • Mechanism of Action:

    • When cancer begins in a cell that has active tumor suppressor genes, these genes can trigger a process leading to the self-destruction of the cell, effectively stopping cancer from developing.

    • This process is known as apoptosis, where the cell initiates a programmed death in response to abnormal conditions that may lead to cancer.

  • Implications on Cancer Risk:

    • Individuals with a higher number of active tumor suppressor genes are less likely to develop cancer.

    • Conversely, those with fewer tumor suppressor genes have an increased risk of cancer.

Oncogenes

  • Definition: Oncogenes are genes that have the potential to cause cancer.

    • Unlike tumor suppressor genes, oncogenes promote cell division and growth without the normal regulatory controls.

  • Activation of Oncogenes:

    • Oncogenes are typically inactive in their normal state but can be activated through mutations or environmental factors such as sun exposure or smoking.

    • When a normal gene is mutated into an oncogene, it contributes to the uncontrolled division of the cell.

  • Mechanism of Action:

    • Oncogenes effectively remove the natural brakes on cell division, leading to over-proliferation of cells. This can lead to tumors that not only grow rapidly but also outcompete nearby cells for nutrients and energy.

Relationship Between Tumor Suppressor Genes and Oncogenes

  • Good vs. Bad Genes: The Dichotomy

    • Tumor suppressor genes are considered beneficial (good) as they help mitigate the risk of cancer by controlling cell growth.

    • Oncogenes are categorized as detrimental (bad) since they encourage unchecked cell division and tumor growth.

  • Exam Preparations:

    • Key questions may revolve around the implications of a high presence of tumor suppressor genes leading to a lower cancer risk, while a high presence of oncogenes leads to an increased cancer risk.

Cancer Risk Prediction Table

  • Table Structure: A framework to analyze the relationship between the prevalence of tumor suppressor genes and oncogenes with cancer risk:

    • Tumor Suppressor Genes

    • Increased Activity - Cancer Risk: Decreases

    • Decreased Activity - Cancer Risk: Increases

    • Oncogenes

    • Increased Activity - Cancer Risk: Increases

    • Decreased Activity - Cancer Risk: Decreases

Role of Chemotherapy in Cancer Treatment

  • Chemotherapy Definition:

    • Chemotherapy is the use of chemical substances to combat cancer cells by halting their division.

    • It involves various types of chemicals that can impact different cellular processes.

  • Effect on Cells:

    • While many normal cells, such as brain cells, are unaffected by chemotherapy due to their non-dividing nature, cancer cells are particularly sensitive as their primary characteristic is uncontrollable division.

    • Chemotherapy can result in the death of cancer cells by enforcing a stop to their division cycle.

    • Side Effects: Patients may experience sickness due to the impact on rapidly dividing normal cells, such as skin and hair cells, leading to hair loss.

  • Challenges with Chemotherapy:

    • Cancer cells can develop resistance to chemotherapy over time, necessitating adjustments in treatment strategies, including combinations of different chemotherapy agents.

Genetic Testing for Cancer Risk

  • BRCA Testing

    • The BRCA test assesses genetic risk factors, particularly relating to breast cancer, by identifying specific oncogenes associated with increased cancer risk.

    • Individuals with a high presence of BRCA oncogenes may opt for preventative measures, like mastectomy, to reduce their risk of developing breast cancer.

    • Personal Anecdote: The speaker's family underwent BRCA testing with resulting decisions made based on high risk.

  • Tumor Suppressor Gene Testing:

    • Inquiry into testing for tumor suppressor genes; generally, the focus is predominantly on oncogenes, as the addition of tumor suppressor genes post-birth is not feasible.

Fascinating Observations about Cancer Resistance in Animals

  • Example: Great white sharks exhibit a low incidence of cancer.

    • Hypothesis: They may possess an abundance of tumor suppressor genes, allowing for immediate tumor suppression upon emergence.

    • Current scientific challenges: Despite studies, no concrete evidence of tumor suppressor genes has been found in great white sharks, leading to speculation on alternative cancer resistance mechanisms.

  • Future Implications: Exploring potential applications for human cancer treatment based on the findings from studies on these species could provide new avenues for cancer therapy.

Conclusion

  • Key Points for Understanding Cancer Genetics:

    • The distinction between tumor suppressor genes and oncogenes is crucial for understanding the genetic basis of cancer.

    • The balance and interaction between these two types of genes significantly contribute to an individual’s cancer risk.

    • Continued research is essential for uncovering novel therapeutic strategies based on genetic insights from both humans and other organisms.