Proto-oncogenes, Oncogenes, Tumor-Suppressor Genes

Question 1

Proto-oncogene

Answer 1

Normal versions of the cellular genes that code for proteins that stimulate normal growth and division.

Question 2

Ras Gene

Answer 2

Ex. Of proto-oncogene

Ras protein (encoded by RAS gene) is a G protein that relays a signal transduction pathway which turns on genes for a protein that stimulates the cell cycle. Normal pathway is triggered by a growth factor that binds to its receptor in the plasma membrane.

Mutations in the Ras gene can lead to the production of a hyperactive Ras protein, which relays the kinase cascade even in the absence of a growth factor. This results in an overexpressed protein that causes increased cell division.

Question 3

Oncogene

Answer 3

Cancer causing gene.

Question 4

Mutations & Cancer

Answer 4

Mutations in proto-oncogenes can lead to cancer. Mutations can arise spontaneously or can be due to environmental influences, such as X-rays or chemical carcinogens.

Question 5

Ways in which a proto-oncogene can be converted into an oncogene

Answer 5

An oncogene arises from a genetic change that leads to an increase either in the amount of the proto-oncogene’s protein product or in the intrinsic activity of each protein molecule. (Campbell)

Question 6

Tumor-Suppressor Gene

Answer 6

Encode proteins that help prevent uncontrolled cell growth. Some tumor-supprssor proteins repair damaged DNA, control cell adhesion, or are components of cell-signaling pathways that inhibit the cell cycle.

Question 7

p53 Gene

Answer 7

DNA damage signals a cascade that actives the p53 gene. The p53 gene promotes transcription of a gene for a protein that inhibits the cell cycle. If the damage cannot be fixed, p53 signals apoptosis, programmed cell death. If there is a mutation in the p53 gene, it cannot promote transcription of the gene for the cell cycle inhibiting gene; increased cell division is a cause of cancer.

Question 8

Which of the following statements describes proto-oncogenes? (Campbell)
A) Their normal function is to suppress tumor growth.
B) They are introduced to a cell initially by retroviruses.
C) They are produced by somatic mutations induced by carcinogenic substances.
D) They can code for proteins associated with cell growth.
E) They are underexpressed in cancer cells.

Answer 8

D) They can code for proteins associated with cell growth.

Question 9

Which of the following is characteristic of the product of the p53 gene? (Campbell)

A) It is an activator for other genes.
B) It speeds up the cell cycle.
C) It causes cell death via apoptosis.
D) It allows cells to pass on mutations due to DNA damage.
E) It slows down the rate of DNA replication by interfering with the binding of DNA polymerase.

Answer 9

A) It is an activator for other genes.

Question 10

Forms of the Ras protein found in tumors usually cause which of the following? (Campbell)
A) DNA replication to stop
B) DNA replication to be hyperactive
C) cell-to-cell adhesion to be nonfunctional
D) cell division to cease
E) growth factor signaling to be hyperactive

Answer 10

E) growth factor signaling to be hyperactive