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Cell Cycle and Cancer

Investigation 3 – Concept Day








Cell Cycle and Cancer: Investigation 3

Concept Day


In this Investigation, we wish to speak more directly about the disease cancer. Over the past two CELLs, Genes and Proteins, and now the first two Investigations of Cell Cycle and Cancer, you have learned much about the way that normal cells grow, divide, and perform functions in tissue.

You have also gained an understanding of the “central dogma” of molecular biology (DNA makes RNA makes protein) and have considered how mutations in the DNA sequence leads to proteins with different functions than normal.

You are now finally in a position to understand how certain mutations may lead to cancer and tumor growth if those mutated proteins are responsible for controlling the cell cycle.



Note: You have seen this slide before when learning about mutations and their impact on human health.

  • In this sequence, a normal cell (on the left) is subjected to several mutations in its DNA. If the sum of the mutations leads to loss of control of the cell cycle, then uncontrolled cell proliferation and cancer may result. The number of stars in the illustration suggests that a series of mutations may be required to ultimately lose control of cell division.
  • As listed on this slide, mutations in a number of different kinds of genes may result in cancer and loss of cell cycle control.
  • DNA repair genes encode proteins that attach to and “proofread” DNA, looking for mismatches in base pairing. Such mistakes or mutations very rarely occur but, once the DNA is altered, the mutation will be copied with all subsequent DNA replications and cell divisions. DNA repair proteins quickly find these mutations and repair them. Obviously, mutations that cause a DNA repair protein to lose function can lead to more and more mutations due to this lack of proofreading and DNA repair.
  • Cell cycle genes encode proteins that either prevent or promote controlled progress of the cell through the cell cycle. You simulated these proteins with the pushpins in Investigation 2 lab.
  • Cell death genes encode proteins that caused the death of certain cells at various points in normal development (also called programmed cell death). Cells targeted will no longer divide. Mutations that compromise the function of cell death proteins can lead to abnormal proliferation of cells and cancer.
  • Cellular differentiation genes encode proteins involved in determining the type of cells formed from groups of undifferentiated precursor or stem cells. Stem cells are very important during embryonic growth and development, where all of the many forms of specialized cells of the body come from these undifferentiated cells. In adults, stem cells are involved in the replenishment and repair of tissue. Mutations in cellular differentiation genes can result in the proliferation of undifferentiated cells.



  • Development of a tumor. Under normal circumstances, cells divide in a controlled manner. Cells in tissues often stop dividing when they come into appropriate contact with other cells in a very organized manner (the red cells in this slide). Many different genes control such “contact inhibition”.
  • When cell cycle control is lost, contact inhibition may no longer prevent cells in a tissue to stop dividing and a tumor can form (the blue cells in this slide). Obviously, this mass of abnormal cells can alter the function of the organ in which it is found.
  • A tumor that stays localized to a single mass may not cause a great deal of problems. However, there is the possibility that some individual cells from the tumor may break off and travel to other areas of the body. This process is known as metastasis and is discussed on the next slide.



  • At the right, a mass of tumor cells (blue cells) are seen to grow out of the tissue and enter the bloodstream. This is a form of metastasis. Clearly, metastasis of cancer cells is very bad because it can distribute uncontrolled cells to various other parts of the body. The cancer spreads.
  • Transport of cancer cells through the circulatory system is not the only way metastasis can occur. Cancer cells can also be transported through body cavities, the lymphatic system, and other means.
  • In this slide, cells from the primary tumor are transported to the liver, lung, and bone. Once arriving at these various tissues, metastasized cells may continue to divide and form new tumors in the target organs.



  • We now turn to a look at two very specific types of cancer; lung and breast cancer. You will be able to examine both normal and cancerous examples of these human tissues in Investigation 3 lab.
  • This slide shows a normal chest x-ray on the left and an x-ray from a patient with lung cancer on the right. The mass or tumor is rather large and highlighted by the red arrow.

Note: For reference, the large mass to the right of the vertebral column in both x-rays is the heart. Below the lungs, the diaphragm and organs of the abdomen are seen.



  • This slide shows specimens of a normal human lung and a human lung with a rather large tumor (indicated by the red arrow). In addition, the round inserts show the microscopic image of each type of sample. These were obtained from the same slides you will view in Investigation 3 lab.
  • The lung’s function in gas exchange necessitates a very specific architecture of cells so that air easily infiltrates the tissue and is brought in close contact with blood so that gas can dissolve across cellular membranes. This is reflected in the microscopic image of the normal lung, which has a foam-like appearance (upper left). All such specialized cellular architecture is lost in the tumor cells of lung cancer as seen in the insert at the upper right.



  • This slide simply shows the normal and cancer biopsies again and presents an artist’s drawing taken from each specimen.
  • Notice that the highly organized structures of bronchioles and alveoli in the normal tissue are replaced with packed, undifferentiated cells in the cancer biopsy. Such tumorous tissue obviously can play no part in the normal function of the lung.



  • This slide shows mammograms of a normal human breast (left) and one containing a cancerous mass (right). The red arrow indicates the breast tumor.



  • This slide simply shows normal breast and breast cancer biopsy micrographs (left) and presents an artist’s drawing taken from each specimen (right). You will be able to study these biopsy slides in detail in Investigation 3 lab.



  • Breast cancer facts. There are many excellent sites on the Internet to learn more about breast cancer. Statistical information for this slide and the next, for example, were obtained from the National Breast Cancer Foundation website.



  • Progress and hope.



  • A challenge and invitation for you to join the research and fight against cancer in your own career. Keep studying!