Question

Define multihit hypothesis. A complete definition will include the following (4pts):

·Define the term “hit”.(1)

Accumulation of mutations in genes that control cell cycle, apoptosis, and cell migration in a adult stem cell.

·Define how many hits normally will cause a cell to become cancer.(1)

·Explain the type of cell that normally becomes a cancer cell and why.(1)

·Finally, make sure to explain the importance of time in a cell becoming a cancer cell.(1)

Answer 1

The 'multihit hypothesis' proposes that a series of mutational events are required for a cell to become cancerous. The term 'hit' denotes mutations in genes controlling and regulating cell cycle and apoptosis. Normally two hits are required for a cell to become cancerous according to the 'two-hit hypothesis' by Knudson. Epithelial cells form most cancers because of their increased rates of proliferation.

A cell might first lose activity of a cell cycle inhibitor causing rapid cell division. These cells might form a benign tumor.Over time, a mutation might take place in one of the descendant cells, causing increased activity of a positive cell cycle regulator. The mutation might not cause cancer by itself either, but the offspring of this cell would divide even faster, creating a larger pool of cells in which a third mutation could take place. Eventually, one cell might gain enough mutations to take on the characteristics of a cancer cell and give rise to a malignant tumor, a group of cells that divide excessively and can invade other tissues. Hence, this might take several cell cycles and time is important in cancer formation.