B5C

Oncogenes are mutated forms of genes. Oncogenes can transform a cell into a tumor cell. Some tumor cells are benign, while others are malignant. How does the presence of an oncogene lead to the formation of a tumor?

• ATP production is inhibited

• Cell division is unregulated

• Somatic cell growth is inhibited.

• Antibody activity is unregulated

Cells typically respond to DNA damage in three ways: by ceasing to grow and divide until the damage is repaired, by permanently ceasing to grow and divide, or by dying. In 2010 a group of scientists reported that a certain kind of immune reaction can cause DNA damage that leads to a fourth response . DNA damage can turn off genes involved in cell-signaling pathways. Turning off these genes can cause less-mature cells to divide too rapidly, often

leading to the development of -

• tumors

• allergies

• hemophilia

• cardiovascular disease

Atherosclerosis is a disease that obstructs blood flow and, therefore, oxygen supply to target organs. A major component of atherosclerosis is the excessive reproduction of smooth muscle cells of the blood vessels. Certain drugs may have the potential to reverse or prevent the

unregulated reproduction of the diseased blood-vessel cells. Which of these processes is the most likely target of these drugs?

• Cell division

• Erythroblast differentiation

• DNA transcription

• Cellular respiration

The diagram below represents the cell cycle.

When cells leave the cell cycle, they exit during G₁ phase and then enter G₀ phase, a resting period. Most normal cells can leave G₀ phase and reenter the cell cycle at G₁ phase before entering S phase. Cancer cells are different because they can not enter G0 phase and are likely to do which of the following?

• Fai l to complete S phase

• Mutate during G₁ phase

• Repeat the cell cycle continuously

• Die after completing mitosis