Question

3. While many cancers in animal hosts (chicken, cats dogs) are caused by retroviruses, this is not the case for humans (6pts total; 2pts each). a. Explain the reason for this difference; b. Describe three main mechanisms of oncogene activation in human cells and provide a detailed example for each of the mechanisms; c. Why there are no inherited cancer syndromes in humans that are caused by activation of an oncogene?

*Please type answer, hard to read answers that are hand written. Thank you!

Answer 1

a. Retroviruses needs a specific membrane protein in order to bind to the host cell. The animal retrovirus is not able to bind to the human host cell because of the lack of the specific membrane protein.

b. Three mechanisms of oncogene activation are below:

1. Point mutation in the single base pair in the proto oncogene.

Example: Ras oncogene. When there is a mutation causing substitution of amino acid Glycine at 12 or glutamine at 61 with any other amino acid, the cleaving of GTP with Ras is slowed. Thus causing the protein to remain active even when there is no signal for cell proliferation, leading to uncontrolled growth

2. Gene amplification leading to expression of multiple copies of proto oncogene.

Example: amplification of c-myc proto oncogene. This causes amplified expression of c-Myc protein causing overgrowth of cells. c-Myc protein regulates G1-S phase of the cell cycle.

3. Chromosomal translocation- when the part of a chromosome gets physically translocated to a different position in the chromosome.

Example: Translocation of c-Myc in chromosome 8 to immunoglobulin gene in chromosome 2, 14 and 22 causing the c-Myc protein to over express and disrupting cell cycle regulation.

c. Cancers are generally caused by the mutation in the somatic cells and not the germline cells. Hence are not passed down the generations. A parent may pass down a predisposition to certain types of cancers making them vulnerable to such cancers.