Question 1

Constitutive activation of the Ras protein is observed in many cancers.Which type of abnormality in the Ras protein is most likely to cause cancer?

Accepted Answer

The Ras protein is a monomeric G protein in a signaling cascade that activates MAP kinases in response to the activation of mitogen receptors on the cell surface.Like all G proteins, Ras has to hydrolyze its bound GTP in order to revert to the inactive state.If it cannot hydrolyze its GTP, it remains switched on forever.

Question 2

The cell cycle is regulated by extracellular signals called mitogens.The cyclin that is most likely to be elevated directly in response to mitogen action is:

Accepted Answer

Mitogen-induced rises in cyclin D trigger the formation of cyclins E and A, which bring the cell through the G₁ checkpoint and S phase.

Question 3

A type of somatic mutation that inhibits apoptosis and thereby permits the survival of deviant cells is:

Accepted Answer

Phosphatidylinositol-3,4,5-trisphosphate activates the protein kinase Akt (protein kinase B).This signaling pathway inhibits apoptosis.

Question 4

The function of caspases is:

Accepted Answer

The caspases are proteases that are activated either in response to the activation of death receptors on the cell surface or by the mitochondrial system, which leads to the formation of an "apoptosome" in the cytoplasm.

Question 5

In most individuals with inherited colon cancer susceptibility who do not have excessive numbers of benign and premalignant polyps, the cancer susceptibility is caused by a heterozygous defect in a gene for:

Accepted Answer

This is a repair system that is especially important for rapidly dividing cells such as those in the intestinal mucosa.

Question 6

Breast cancer is diagnosed in a 62-year-old woman.She already survived a soft-tissue sarcoma that had been diagnosed and successfully treated when she was 40 years old and an adrenocortical cancer that had been diagnosed and successfully treated when she was 48 years old.She probably has an inherited cancer susceptibility that affects:

Accepted Answer

Breast cancer susceptibility occurs not only in mutations of BRCA1 and BRCA2 but also in Li-Fraumeni syndrome, which is caused by inherited mutations in one copy of the p53 gene.

Question 7

In order to push the cell through the G₁ checkpoint, the cyclin-dependent kinases have to phosphorylate:

Accepted Answer

The protein pRb is the "guardian of the G₁ checkpoint." It prevents transcriptional activation by E2F, until both pRb and E2F become phosphorylated by cyclin-dependent kinases.

Question 8

Progression through the early stages of mitosis requires the phosphorylation of many nuclear proteins, including chromosomal scaffold proteins and the lamins.The cyclin that is most directly involved in these phosphorylations is:

Accepted Answer

Cyclin B is the "G₂ cyclin" that pushes the cell into mitosis.It is degraded suddenly during mitotic metaphase.

Question 9

Cytochrome c is normally attached to the outer surface of the inner mitochondrial membrane, where it participates in electron transport.However, when released into the cytoplasm, it can influence the fate of the cell by:

Accepted Answer

This is the "mitochondrial" pathway to programmed cell death.

Question 10

Cervical cancer is often described as a "sexually transmitted cancer" because infection with papillomavirus (wart virus) is a major risk factor.The strains of human papillomavirus that promote cervical cancer do so by:

Accepted Answer

This normally leads to mitosis and promotes the survival of the virus-infected cells.It is likely to lead to cancer only if the viral genes become accidentally incorporated in one of the host cell chromosomes.

Question 11

Akt (protein kinase B) is a protein kinase whose activation causes, among other effects:

Accepted Answer

The answer of Akt (protein kinase B) is a protein...

Question 12

Loss of heterozygosity in genomic locations close to the site of the mutation is observed in the malignant tumors of many patients with inherited cancer susceptibility.The most likely cause for loss of heterozygosity in these patients is:

Accepted Answer

Loss of heterozygosity can also be caused by large deletions, mitotic nondisjunction, or gene conversion.But mitotic crossing over seems to be the most common mechanism.

Quiz 18: Cellular Growth Control and Cancer