11.4 Cancer and the Cell Cycle

Path of faulty P53

Does not trigger P21 P21 doesn't block CdK activation

Human papillomavirus can cause cervical cancer. The virus encodes E6, a protein that binds p53. Based on this fact and what you know about p53, what effect do you think E6 binding has on p53 activity?

E6 binding marks p53 for degradation

___________ are changes to the order of nucleotides in a segment of DNA that codes for a protein.

Gene mutations

P53

Mutated gene found in 50% of all cancer cells

List the regulatory mechanisms that might be lost in a cell producing faulty p53.

Regulatory mechanisms that might be lost include monitoring of the quality of the genomic DNA, recruiting of repair enzymes, and the triggering of apoptosis.

tumor suppressor genes

Segment of DNA that codes for regulator proteins that prevents the cell from undergoing uncontrolled division - Rb -P53 -P21

A mutated gene that codes for an altered version of Cdk that is active in the absence of cyclin is a(n) _____.

oncogene

Which molecule is a Cdk inhibitor that is controlled by p53?

p21

A gene that codes for a positive cell cycle regulator is called a(n) _____.

proto-oncogene

p53 can trigger apoptosis if certain cell-cycle events fail. How does this regulatory outcome benefit a multicellular organism?

If a cell has damaged DNA, the likelihood of producing faulty proteins is higher. The daughter cells of such a damaged parent cell would also produce faulty proteins that might eventually become cancerous. If p53 recognizes this damage and triggers the cell to self-destruct, the damaged DNA is degraded and recycled. No further harm comes to the organism. Another healthy cell is triggered to divide instead.

Explain the difference between a proto-oncogene and a tumor-suppressor gene.

A proto-oncogene is a segment of DNA that codes for one of the positive cell cycle regulators. If that gene becomes mutated so that it produces a hyperactivated protein product, it is considered an oncogene. A tumor suppressor gene is a segment of DNA that codes for one of the negative cell cycle regulators. If that gene becomes mutated so that the protein product becomes less active, the cell cycle will run unchecked. A single oncogene can initiate abnormal cell divisions; however, tumor suppressors lose their effectiveness only when both copies of the gene are damaged.

Outline the steps that lead to a cell becoming cancerous.

If one of the genes that produce regulator proteins becomes mutated, it produces a malformed, possibly non-functional, cell-cycle regulator. This increases the chance that more mutations will be left unrepaired in the cell. Each subsequent generation of cells sustains more damage. The cell cycle can speed up as a result of loss of functional checkpoint proteins. The cells can lose the ability to self-destruct.

Oncogene

mutated version of a normal gene involved in the positive regulation of the cell cycle

Proto-oncogenes

normal cellular genes that are important regulators of normal cellular processes, they promote growth. alterations in the expression of these cells result in oncogenes