Question 1

Many normal genes that have important functions in cells sometimes acquire mutations that cause the products of these genes to have negative effects, including the development of cancer. These genes are called:

Accepted Answer

Proto-oncogenes are normal genes that can become oncogenes due to mutations or increased expression, leading to cancer.

Question 2

Proto-oncogenes:

Accepted Answer

Proto-oncogenes can become oncogenes, which may trigger cancer, through mutations caused by various factors, including cigarette smoke. Proto-oncogenes normally play roles in cell growth and division, but when mutated, they can contribute to the development of cancer.

Question 3

Phosphorylated p53 is a protein that accumulates in the nucleus of a cell that has damaged DNA. The p53 gene that encodes this protein is an example of a(n):

Accepted Answer

Tumor suppressor genes, such as p53, normally function to inhibit the development of cancer by regulating cell growth and division. When the DNA is damaged, p53 functions to halt the cell cycle and repair the damage or induce apoptosis, which prevents the proliferation of potentially harmful cells. Mutations in tumor suppressor genes can result in their loss or malfunction, leading to uncontrolled cell growth and the development of cancer.

Question 4

A woman has her genome sequenced and finds that she carries a mutation in p53. Will she develop cancer?

Accepted Answer

Mutations in p53 are well-known to be associated with an increased risk of developing certain types of cancer, such as breast, ovarian, and colorectal cancer. However, it is not a certainty that the woman will develop cancer, as other factors such as environmental exposures and lifestyle choices can also influence cancer risk.

Question 5

How would the loss of p53 activity affect a cell?

Accepted Answer

Loss of p53 activity would affect all of these aspects in a cell. The p53 protein plays a crucial role in regulating the cell cycle and responding to DNA damage. Without p53 function, the checkpoints that monitor DNA damage and ensure repair before entering mitosis, such as the G₁/S checkpoint, would not be functional. Additionally, p53 plays a role in preventing the replication of cells with damaged DNA, which could lead to the accumulation of DNA damage. Finally, p53 regulates CDK activity, which is necessary for progression through the cell cycle. Without proper regulation of CDK activity, cells could enter mitosis with damaged DNA or in an uncontrolled manner, leading to genomic instability and potentially cancer.

Question 6

Some types of leukemia are the result of constitutively active (i.e., "always on") growth factor receptors.

Accepted Answer

This statement is true. In some cases of leukemia, there are mutations in genes that code for growth factor receptors which cause them to be "always on" and promote uncontrolled cell growth. This is a common mechanism in certain types of leukemia, such as chronic myelogenous leukemia (CML).

Question 7

Which of the following would be MOST likely to lead to the development of cancer?

Accepted Answer

Activation of an oncogene and inactivation of a tumor suppressor gene are the two main events that contribute to the development of cancer. Activation of proto-oncogenes alone is not sufficient to cause cancer, and activation of tumor suppressor genes is actually beneficial in preventing cancer. Activation of both an oncogene and a tumor suppressor gene could potentially cancel out the effects of each other, and not lead to cancer development.

Question 8

An enzyme that catalyzes the addition of a phosphate group from ATP to another molecule is called a:

Accepted Answer

A kinase is an enzyme that catalyzes the addition of a phosphate group from ATP to another molecule. This process is called phosphorylation. A phosphatase, on the other hand, catalyzes the removal of a phosphate group from a molecule. A phosphorylase is an enzyme that catalyzes the addition of a phosphoryl group from an inorganic phosphate to an acceptor molecule, not from ATP. A cyclase catalyzes the cleavage or synthesis of a cyclic compound.

Question 9

Which of the following statements is TRUE if a cell has a mutation in the p53 gene such that the p53 protein is no longer able to be phosphorylated?

Accepted Answer

When p53 is phosphorylated, it can activate genes involved in cell cycle arrest, DNA repair, or apoptosis. If p53 cannot be phosphorylated, it would not be able to carry out these functions, and the cell may continue to proceed through the cell cycle even in the presence of DNA damage.

Question 10

In a normal cell, tumor suppressors are responsible for:

Accepted Answer

Tumor suppressors are responsible for preventing the formation and growth of tumors. They achieve this by either repairing DNA replication errors (option B) or signaling that highly defective cells be destroyed (option C). Therefore, they do not increase cell division rates (option A), nor do they signal DNA replication to begin (option D).

Question 11

Which of the following is considered a proto-oncogene?

Accepted Answer

All of these choices are considered proto-oncogenes because mutations in any of these genes can lead to uncontrolled cell growth and ultimately cancer. For example, a mutation in a cell-surface receptor gene could lead to overactive signaling pathways that promote cell growth, while a mutation in a growth factor gene could result in excessive production of that growth factor, also promoting cell growth. Similarly, mutations in genes encoding protein kinases or G-proteins can disrupt normal signaling pathways and contribute to tumorigenesis.

Question 12

A proto-oncogene is a "normal" gene that, if mutated, can become an oncogene and lead to a cell becoming cancerous.

Accepted Answer

This is correct. Proto-oncogenes are "normal" genes that regulate cell growth and division, but if they undergo certain mutations or changes, they can become oncogenes and contribute to the development of cancer.

Question 13

The first oncogene to be discovered:

Accepted Answer

All of the statements accurately describe characteristics of the first oncogene discovered. It contributes to uncontrolled cell division or cancer (A), was identified in the Rous sarcoma virus (B), is a type of protein kinase promoting cell division (C), and has a less-active normal counterpart known as a proto-oncogene (D).

Question 14

Which of the following is NOT a hallmark of malignant cancer?

Accepted Answer

All of these choices are hallmarks of cancer. Cell division in the absence of growth signals, resistance to signals that slow cell division or promote death, metastasis, and ability to stimulate growth of blood vessels to provide nutrients to the rapidly growing tumor are all characteristics of malignant cancer.

Question 15

Malignancies develop stepwise over time because:

Accepted Answer

Malignancies develop stepwise over time because it takes multiple mutations of multiple genes to allow cancer cells to develop. This process can occur over a period of years, allowing for the accumulation of genetic changes that eventually lead to the development of a malignant tumor. The other choices listed do not fully explain the stepwise progression of malignancies.

Question 16

Recall the experiments of Rous and colleagues. If he had found that filtered cancer cell extract could not cause cancer when injected into healthy animals, what could he have deduced?

Accepted Answer

Rous's experiments involved filtering cancer cell extracts to remove any cells or large particles, then injecting the filtered extract into healthy animals. If the filtered extract could not cause cancer, it would suggest that the cancer-causing agent was not a small, filterable agent (like a virus), but rather something larger that was removed by the filtering process. This could imply that intact cancer cells, bacteria (which are larger than viruses and would be removed by the filter), or large proteins (which could also be filtered out) might be necessary to cause cancer. Therefore, all of the given choices are correct deductions based on the hypothetical outcome that the filtered extract could not cause cancer.

Question 17

Tumor suppressors oppose oncogenes by:

Accepted Answer

Tumor suppressors can perform all of the listed functions to oppose the activity of oncogenes and prevent the development of cancer. They can slow down cell division, repair mutations, instruct defective cells to undergo apoptosis, and block the action of oncogenes. By doing so, they help maintain genome stability and prevent the accumulation of genetic damage that can lead to uncontrolled cell growth and tumor formation.

Question 18

Cell cycle checkpoints:

Accepted Answer

All of these choices are correct. Cell cycle checkpoints act as a brake on cell division if something is not right, provide opportunities to check if the cell has carried out steps necessary for cell division, and can involve the protein p53.

Question 19

Cancer-causing genes found in some viruses are called:

Accepted Answer

Genes found in some viruses that cause cancer are called oncogenes. Proto-oncogenes are normal genes in the cell that can become oncogenes if they are mutated or activated inappropriately. Tumor suppressor genes are normal genes that, when functioning properly, help prevent the development of cancer. Viral genes refer to genes found in the genome of a virus.

Question 20

Which of the following statements about viruses is TRUE?

Accepted Answer

None of the statements are true. Viruses are not cells and do not have multiple genes that are all oncogenes. While some cancers are caused by viruses, not all cancers are caused by viruses. Finally, human cancers have been associated with viruses, such as HPV and Hepatitis B.

Quiz 11: Cell Division: Variations, Regulation, and Cancer