Problem 16 - Biology

Question

Which of the following statements about cancer is false? (a) Oncogenes arise from mutations in proto-oncogenes. (b) Tumor suppressor genes normally interact with growth-inhibiting factors to block cell division (c) More than 100 oncogenes and 15 tumor suppressor genes have been identified (d) Oncogenes were first discovered in mouse models for cancer (e) The development of cancer is usually a multistep process involving both oncogenes and mutated tumor suppressor genes

Step-by-Step Solution

Answer

Statement (d) is false; oncogenes were discovered in viruses, not mice.

Step 1: Understand Each Statement

First, let's break down each statement to understand their meanings. (a) Oncogenes arise from mutations in proto-oncogenes. This states that oncogenes, which can cause cancer, originate from proto-oncogenes when they mutate. (b) Tumor suppressor genes normally interact with growth-inhibiting factors to block cell division, suggesting they prevent uncontrolled cell division. (c) More than 100 oncogenes and 15 tumor suppressor genes have been identified indicates a certain number of these genes have been found. (d) Oncogenes were first discovered in mouse models for cancer implies the initial discovery of oncogenes came from mice. (e) The development of cancer is usually a multistep process involving both oncogenes and mutated tumor suppressor genes emphasizes the complexity of cancer development.

Step 2: Evaluate Statement (a)

Statement (a) is true. Oncogenes do arise from proto-oncogenes. Proto-oncogenes are normal genes that can become oncogenes due to mutations or increased expression.

Step 3: Evaluate Statement (b)

Statement (b) is also true. Tumor suppressor genes act as a safety mechanism to prevent cells from dividing uncontrollably by interacting with growth-inhibiting factors.

Step 4: Evaluate Statement (c)

Statement (c) is true. Modern research has identified over 100 oncogenes and approximately 15 tumor suppressor genes.

Step 5: Evaluate Statement (d)

Statement (d) is false. Oncogenes were first discovered in viruses, specifically the Rous sarcoma virus in chickens, not in mouse models.

Step 6: Evaluate Statement (e)

Statement (e) is true. The development of cancer is typically a complex process involving multiple steps, including changes in oncogenes and tumor suppressor genes.

Key Concepts

Oncogenes

Oncogenes are a type of gene that have the potential to cause cancer. They are derived from proto-oncogenes, which are normal genes that help regulate cell growth and division. However, when proto-oncogenes undergo mutations or their expression increases abnormally, they can turn into oncogenes. This transformation results in uncontrolled cell growth and division, which may lead to the formation of tumors.
For example, a mutation may allow a proto-oncogene to remain active permanently, continuously sending signals for cell division without the usual controls in place.

• Proto-oncogenes are normal and necessary for regular cellular functions.
• Mutations can convert them into oncogenes.
• Oncogenes lead to unchecked cell proliferation, a hallmark of cancer.

The study of oncogenes is crucial in cancer biology because understanding how these genes operate can aid in developing targeted cancer therapies. Scientists aim to find methods to either turn off oncogenes or prevent their activation to combat cancer effectively.

Tumor Suppressor Genes

Tumor suppressor genes act as guardians of the cell, preventing excessive cell growth and division. They work by interacting with various growth-inhibiting factors, signaling the cell to stop dividing or to self-destruct in the case of damage.
A classic example of a tumor suppressor gene is the p53 gene, often called the "guardian of the genome." It can prompt the repair of DNA damage or initiate cell death if the damage is irreparable.

• Tumor suppressor genes help regulate and balance cell division.
• Mutations in these genes can impair their regulatory function, leading to cancer.
• They act as a cellular brake system to keep cell growth in check.

Loss of function in these genes due to mutations can remove this cellular brake, allowing cells to grow and divide unchecked, thus contributing to cancer development. Therefore, the integrity and functionality of tumor suppressor genes are vital in preventing cancer.

Cancer Development Process

The development of cancer is a complex, multistep process that involves both oncogenes and tumor suppressor genes. Initially, a mutation may activate an oncogene or deactivate a tumor suppressor gene, leading to early-stage tumor formation.
However, cancer development usually requires several genetic changes over time. This process, known as tumor progression, involves multiple mutations and environmental factors that conspire to create increasingly aggressive cancer cells.

• Cancer development is rarely the result of a single event.
• A series of genetic mutations must occur before a cell becomes cancerous.
• Both the activation of oncogenes and inactivation of tumor suppressor genes contribute to tumorigenesis.

Recognizing the multistep nature of cancer allows researchers to identify various stages of potential intervention. By understanding each step in the cancer development process, new targeted therapies can be designed to interrupt the progression and treat or prevent cancer.