Deck 26: Cancer Cells

Question 1

Normal Cells and Cancer Cells. You are given two test tubes, one containing cells from a human cancer and the other containing normal cells. Before you begin your studies, the labels fall off the test tubes. Describe at least four experiments you could carry out to determine which sample contains the cancer cells.

Answer 1

Cancer cells are cells that have uncontrolled growth. When cells divide continuously, it can lead to the formation of tumors or a concentration of growing cells.
Since normal cells do not form tumors, the cells from each test tube can be differentiated by the cells growth patterns. For example, both samples of cells can be injected into a mouse or grown in isolation on a medium. The sample that grows in mass and forms tumors contains the cancer cells.
Another feature that distinguishes cancer cells from normal cells is that cancer cells are anchorage-independent. This means that the cells can grow in a liquid medium without being attached to a surface. On the other hand, normal cells need a surface to adhere to for growth. Therefore, the cell sample that proliferates in a liquid medium contains the cancer cells.
When grown in a culture, normal cells only grow in a single layer. However, cancer cells continue to divide after a single layer of cells has been formed. Therefore, the cancer cells will have a higher density when grown in culture.
In normal cells, the length of the telomere shortens after every round of cell division. However, cancer cells have mechanism for maintaining the length of their telomeres. This allows cancer cells to continue growing without triggering apoptosis or cell death. Therefore, observing the telomere length of each sample after division can be used to distinguish the normal cells from the cancer cells. The normal cells will have telomeres that shorten over time.

Question 2

Phorbol Esters and Cancer. The active ingredient in croton oil is a phorbol ester, which mimics the effects of the molecule diacylglycerol (DAG). Based on what you know about DAG (see Chapter 23), explain in detail why it might be an effective promoter, but not initiator, of tumor formation.

Answer 2

The synthesis of the compound diacylglycerol is activated by tumor promoters. In itself diacylglycerol will not promote tumors. It functions as a secondary messenger in the body.
It participates in the transport of protein kinase C enzyme too. It also activates protein kinase C.
Since DAG takes an active part in the biochemical processes of the body and in the signaling pathway, it cannot be a promoter of tumors. But tumor cells produce DAG which gives them resistance to ionizing radiation.
So DAG does not behave as an initiator but it can behave as a promoter in tumor formation.

Question 3

Angiogenesis. Describe two pieces of evidence supporting the idea that angiogenesis is required for tumors to grow beyond a tiny clump of cells, and two pieces of evidence supporting the idea that cancer cells secrete molecules that stimulate angiogenesis.

Answer 3

Angiogenesis is the growth of new blood vessels. The endothelial lining on the inner wall of the blood vessels migration, growth and differentiation is referred through the phenomenon of angiogenesis; which is controlled by various chemical signal in the body.
Cancer cells need access to the blood stream, which carries nutrients, in order, to continue growing. It has been shown that tumors are unable to grow beyond a small clump of cells without a blood supply.
In one experiment, cancer cells injected into a thyroid could not grow because they were unable to access the thyroids blood vessels. On other hand, cancerous cells isolated from thyroid gland when given required nutrients, kept them alive.
In second experiment, one group of cancer cells was injected in the anterior chamber of a rabbit's eye with no blood vessels. Another group of cancer cells was injected into the iris near a group of blood vessels.
Both cancer cell groups survived, the group on the iris grew much larger than the group anterior chamber of the eye.
While cancer cells can grow in the presence of an available blood supply, there also evidence that the cancer cells can create their own blood supply by secreting molecules that trigger angiogenesis.
When cancer cells encased in a filter are injected into animal cells, new blood vessels grow through the pores of the filter and attach to the tumor. When normal cells in a filter are injected into a cell, no blood vessels form.

Question 4

Rats, Guinea Pigs, and Humans. The chemical substance 2-acetylaminofluorene (AAF)causes bladder cancer when injected into rats but not guinea pigs. If normal bladder cells obtained from rats and guinea pigs are grown in culture and exposed to AAF, neither are converted into cancer cells. How can you explain these findings Does your explanation suggest how to predict whether AAF is carcinogenic in humans without actually exposing humans to AAF

Question 5

Oncogenes and Tumor Suppressor Genes. Indicate whether each of the following descriptions applies to an oncogene (OG), a proto-oncogene (PO), or a tumor suppressor gene (TS). Some descriptions may apply to more than one of these gene types. Explain your answers.
(a)A type of gene found in normal cells.
(b)A gene that could code for a normal growth factor.
(c)A type of gene found in cancer cells.
(d)A type of gene found only in cancer cells.
(e)A gene whose presence can cause cancer.
(f)A gene whose absence can cause cancer.
(g)A type of gene found in normal cells and cancer cells.

Question 6

Viruses and Cancer. Based on what you know about viruses and their means of reproduction, explain why many oncogenic viruses interact with tumor suppressor proteins.

Question 7

Children of the Moon. Children with xeroderma pigmentosum usually cannot carry out excision repair. Why does this makes them so susceptible to developing cancer
Why was the word "usually" included in the first sentence

Question 8

Cancer Screening. The annual incidence of colon cancer in the United States is about 55 cases per 100,000. Because colon cancer often causes bleeding, doctors sometimes use a screening procedure called the fecal occult blood test (FOBT)to look for tiny amounts of blood in the feces. One form of this test has a specificity of about 98%, which means that when it indicates the presence of blood in the feces, the result is an error (i.e., cancer is not present)only 2% of the time. While this may seem like excellent specificity, a 2% "false positive" rate makes this test almost useless as a tool for colon cancer screening. Why