Question

Environmental agents may cause epigenetic changes that alter the expression of specific genes. Which of the following epigenetic changes would be expected to promote cancer? a. a change that resulted in the overexpression of a tumor-suppressor gene b. a change that resulted in the inhibition of a tumor-suppressor gene c. a change that resulted in the overexpression of an oncogene d. a change that resulted in the inhibition of an oncogene e. Both b and c are correct.

Short answer

The correct answer is e. Both b and c are correct.

Step-by-step solution

Analyze the options

Read through each of the options a, b, c, d, and e, and consider whether each change would result in promoting cancer. This requires understanding the role and function of oncogenes and tumor-suppressor genes.

Evaluate Option a

'a' says a change results in the overexpression of a tumor-suppressor gene. Overexpressing a tumor-suppressor gene would result in less cell division and more cell death. Therefore, this cannot promote cancer.

Evaluate Option b

'b' says a change that resulted in the inhibition of a tumor-suppressor gene. If a tumor-suppressor gene is inhibited, cell division can occur more readily because there's less control over cell growth. This could potentially lead to cancer.

Evaluate Option c

'c' is a change that results in the overexpression of an oncogene. Overexpression of an oncogene promotes cell growth and division, bypassing the normal checks and balances that prevent uncontrolled growth. Consequently, this would promote cancer.

Evaluate Option d

'd' is a change that results in the inhibition of an oncogene. If an oncogene were inhibited, it would prevent excess cell growth and potentially limit cancer formation. Therefore, this can't result in promoting cancer.

Evaluation Option e

Option 'e' says 'Both b and c are correct', implying that both inhibition of a tumor-suppressor gene and overexpression of an oncogene would promote cancer. Since both Options b and c independently promote cancer, Option e correctly synthesizes this information.

Key concepts

Tumor-Suppressor Gene

Tumor-suppressor genes play a crucial role in regulating cell division and maintaining the health of our cells. They act as the body's natural defense against uncontrolled cell growth. These genes work to inhibit cell division and promote cell death, ensuring that damaged or faulty cells do not survive or proliferate.

• If a tumor-suppressor gene is functioning properly, it helps prevent cancer by stopping cells from dividing uncontrollably.
• However, if these genes are inhibited or not expressed properly due to epigenetic changes, the risk of cancer increases, as they cannot control cell growth adequately.

It's similar to a car's brakes; without them, the car may speed out of control, just like cell division without tumor-suppressor genes.

Oncogene

Oncogenes are like the gas pedal in a car—increasing the rate of cell growth and division. In their normal state, they are called proto-oncogenes. These genes are involved in essential cellular functions like growth and differentiation.

• When these genes become mutated or excessively expressed, they transform into oncogenes, leading to uncontrolled cell proliferation.
• Primary triggers for converting a proto-oncogene to an oncogene include genetic mutations, viral infections, or epigenetic changes.

When an oncogene is overexpressed, the cell loses its ability to regulate growth resulting in tumor formation and cancer.

Cancer Promotion

Cancer promotion occurs when certain genetic changes drive the cell cycle to speed up, leading to uncontrolled division and tumor formation. Epigenetic modifications, such as DNA methylation or histone modification, can disrupt normal gene function.

• Inhibiting tumor-suppressor genes promotes cancer by removing the control mechanisms that keep cell division in check.
• Overexpression of oncogenes accelerates cell division, bypassing the body's normal regulatory pathways.

Together, these changes create an environment ripe for cancer development by tipping the balance of cell regulation.

Gene Expression

Gene expression is the process by which information from a gene is used to synthesize functional gene products like proteins. This process is tightly regulated by various genetic and epigenetic factors, ensuring that cells function correctly.

• Epigenetic changes can affect gene expression without altering the DNA sequence itself. For example, methylation can suppress gene activity.
• Alterations in gene expression, such as the overexpression of oncogenes or inhibition of tumor-suppressor genes, can lead to diseases, including cancer.

Understanding gene expression helps in grasping how changes in genetic information can have catastrophic effects like cancer.

Cell Division

Cell division is a fundamental biological process where a parent cell divides into two or more daughter cells. It's vital for growth, development, and repair in multicellular organisms.

• Normal cell division is subject to various regulatory mechanisms, ensuring that new cells are created only when needed.
• Disruption in this regulated process, often due to genetic changes, can lead to uncontrolled cell division—a hallmark of cancer.

By maintaining a balance between cell division and cell death, the body's tissues remain healthy. Tumor-suppressor genes and oncogenes are critical parts of this balance.