Module 5
1. Module 5
1.11. Page 4
Module 5—Cell Division: The Processes of Mitosis and Meiosis
Lesson Summary
During this lesson, you explored the following focusing questions:
- What are the phases of the cell cycle?
- Do all cells have the same ability to reproduce, and does this change with age?
Approximately 50 times in the life of a cell line, healthy cells will move through interphase and M phase. In interphase, from growth and production in G1, to the synthesis of DNA in S phase, and all the way through and including the preparation of G2, the cell is constantly checking its own performance and readiness for the next step in the cycle. Finally, during M phase, the cell will go through a series of stages of division involving chromosomes. Finally, during cytokinesis, the cell will physically divide or split itself in two to form two new young cells, each of which contains one copy of the parent cell’s genetic instructions.
Normal cells have a limit to how many times they can divide, and they communicate and work with the cells around them. Cancerous cells do not respect either of these criteria, and this can have terrible results. If the fountain of youth is to be found by gaining control of cellular division, it will not be by following cancer’s example!
Cancer cells are called “wild cells.” Their life cycle involves only division. They do not enter the interphase stage where cell functions are performed. As you saw in the videos, many of the technologies and treatments of cancer involve controlling the life cycle stages of cancerous cells.
Going Beyond
Nanotechnology is a growing field that currently has an impact on virtually all science disciplines. Use search terms such as “CNN + nanotechnology + cancer + 2005” as a starting point, and then use the library, Internet, or other resources to conduct research on nanotechnology and cancer. Does this technology show promise for winning the fight against cancer? Have any human trials been conducted or considered? What are the risks involved with this technology? Are there enough regulations in place to govern its use? Create a simple report, presentation, or discussion posting to share with your peers or your teacher.
Lesson Glossary
Consult the glossary in the textbook for other definitions that you may need to complete your work.
anchorage dependence: a property of normal cells that only allows mitosis to occur when cells are attached to a substrate or surface, not floating freely
Anchorage dependence is lost in cancer, thereby allowing for metastasis to occur.
cancer: rapid proliferation (cell division) of cells that occurs when mutations result in disruption of the normal timing of mitosis; characterized by loss of density-dependent inhibition, loss of anchorage dependence, dedifferentiation of cell function, rapid metabolism, and short cell cycle
cell cycle: the period between cell divisions; divided into the phases of interphase, mitosis, and cytokinesis; may also be divided into interphase and M phase (mitosis and cytokinesis)
cellular clock: a property of cells that allows them to go through a set number of cell divisions and then stop, whereupon the cell line dies out; sometimes called apoptosis
Cancer cells do not have a normal cell clock so they do not apoptose.
chemotherapy: the use of cytotoxic drugs that inhibit cell division, usually by preventing DNA replication or interfering with the spindle mechanism of mitosis or by interfering with the supply of blood and nutrients to the tumour; applied systemically (into the bloodstream); targets cancerous cells but may also affect rapidly dividing normal cells to some degree
cytokinesis: the phase of the cell cycle after mitosis when the cytoplasm divides into two separate daughter cells
A cleavage furrow forms in animal cells; a division plate forms in plant cells.
density-dependent inhibition: a property of normal cells that allows mitosis to occur only until cells touch each other
Density-dependent inhibition is lost in cancer cells; therefore, cells begin to form on top of one another, forming masses of cells called tumours.
eukaryotic cell: a cell with membrane-bound organelles and nucleus
G1 phase: the first part of interphase where the cell is actively growing and undergoing metabolism and protein synthesis
G2 phase: the third part of interphase where the cell continues growing, metabolizing, and carrying out protein synthesis
Hodgkin’s disease: a blood cancer of lymph tissue
interphase: the longest period of the cell cycle when the cell is actively growing and metabolizing; consists of G1, S, and G2 phases; DNA is in loose, stringy chromatin form not visible under the microscope
M phase: mitosis and cytokinesis together
metastasis: the tendency of some cancer cells to break off from a primary tumour and move through the blood or lymphatic systems to other locations in the body where secondary tumours form; sometimes referred to as the “spreading” of cancer
mutagenic agent: a chemical or physical agent that has the ability to mutate DNA, affecting the timing of the cell cycle; increasing the rate of mitosis
radiation treatment: cancer treatment in which high-energy radiation from radioactive isotopes is directed at a cancerous tumour in an effort to destroy it without destroying surrounding normal tissue
replication: the copying of the cell’s DNA prior to mitosis so that each daughter cell has an exact copy of the mother cell’s genetic material; results in sister chromatids; occurs in the S phase of interphase
S phase: the second part of interphase where DNA replication occurs in preparation for upcoming mitosis; produces sister chromatids
sister chromatids: two pieces of DNA that are identical to each other as a result of DNA replication in S phase; lie side-by-side and are buttoned together by a centromere; together make up one chromosome
spindle apparatus: a structure composed of spindle fibres; forms during prophase in mitosis to facilitate separation and movement of chromosomes in cell division