Module 5 Lesson 2 - 7
Lesson 2 - Mitosis
Reflect and Connect
By producing copies of our DNA in S phase, and then separating those identical sets of DNA carefully into new cells during mitosis, our cells ensure that the next generation has all it needs to continue life. Each new cell has the same number of chromosomes as its parent cell. Consistency seems assured.
However, as mentioned n the introduction, our bodies change over time. For example, our skin is not as elastic as it is was when we were younger. What could be causing this? The source of aging seems to be two-fold. One factor is part of the process of copying of our DNA, and the other is linked to environmental stress.Our environment is harsh. Many chemicals and radiation can break up our DNA or cause changes known as mutations. One common class of these nasty chemicals is known as oxidants. These highly reactive substances contain oxygen and are present always, but they increase with infection as well as with consumption of alcohol, cigarettes, and highly processed foods.
Another concern is high levels of glucose, which can bind to the DNA and cause it to stop functioning. Mutation, oxidants, and high glucose can cause our cells to die. Even if cells escape death, the cell line may be reduced in function forever or may end with cancerous growth.
In addition to environmental stress, our DNA faces challenges from within. Each cell can go through a maximum number of 50 cell divisions. Each time our DNA is copied in S phase, it is not perfectly copied. Instead, the ends of our chromosomes, known as telomeres, are shortened slightly. Telomeres protect the chromosome in much the same fashion a plastic tip protects a shoe lace. When these ends are too short, the chromosomes can no longer be copied nor do they function properly, and the cell dies.
Going Beyond
Nanotechnology is a growing field of study that affects most science disciplines. Consider the following website, Nanotechnology in Cancer
Does this technology show promise in 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?
Lesson Summary
Healthy cells move through interphase and mitotic phase of the cell cycle when conditions are correct. 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 checking constantly its own performance and readiness for the next step in the cycle. During mitotic phase and cytokinesis, the cell divides physically or splits itself in two to form two new young cells, each of which contains one copy of the genetic instructions of the parent cells.
Regular cells have a limit to how many times they can divide, and they respect their neighbours. Cancerous cells do not respect either of these criteria, and this can have terrible results.
Throughout our life cycle, our bodies require continual renewal. In dealing with environmental stress or cases of injury, our cells die and must be replaced. Mitosis provides very quick and effective cell division. Starting with just one cell, mitotic division quickly covers a damaged area or infected tissue with healthy new cells. These new cells all function as their parent cell did, have the same number of chromosomes, and are nearly genetically identical. Consider your family again; not all members have mitotic division at the same rate or effectiveness. A sister or brother entering a growth spurt has dramatic mitosis rates. Grandparents or great-grandparents have many cell lines that can no longer reproduce new cells effectively. The shorter cycle of our cells eventually puts a limit on our body's life cycle.
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?
- What are the phases of mitosis? Explain.
- How does mitosis maintain consistency in plants and animals?
Mitosis is the orderly separation of doubled chromosomes into new daughter cells. Through prophase, metaphase, anaphase, and telophase, the cell carefully ensures each new cell has a complete set of chromosomes. By this division, plant or animal tissue lines are continued faithfully until time and exposure to the environment cause a breakdown with age.
Assignment
Complete the Lesson 2 set of questions in Assignment 5A and Assignment 5C