BIO 105 1st Edition Lecture 6Outline of previous LectureI. How do people get their genetic traits?II. How does DNA work?How is DNA passed on?How can we use DNA to identify the source of biological sample?Outline of Current LectureI. How do cells reproduce themselves and properly copy their genetic material?II. What causes cancer?III. How can cancer be controlled or prevented?IV. How do gametes get the proper genes to pass on to the next generation?Current LectureBiology 105 Cell Division and CancerEssential Questions 1. How do cells reproduce themselves and properly copy their genetic material?2. What causes cancer?3. How can cancer be controlled or prevented?4. How do gametes get the proper genes to pass on to the next generation? Interactive Class NotesHow do cells reproduce themselves and properly copy their genetic material?I. Mitosis A. Chromosomes carry information needed for cells and organs, so they must be correctly replicated and distributed to new cells. B. Each species has a characteristic number of chromosome types. Humans have 23 chromosome types and fruit flies have 4. 1. Diploid (2N) organisms have two of each type of chromosome in their cells. How do they get two? These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is bestused as a supplement to your own notes, not as a substitute.a. Diploid human cells have 46 chromosomes; diploid fruit fly cells have 8. Most cells in the bodyare diploid. 2. The two chromosomes of the same type are called homologs; they form a homologous pair. Each member of the pair has the same genes on it. 3. Haploid cells (1N) have one of each type of chromosome. This is only found in the gametes (eggs and sperm). Each human egg and sperm cell has 23 chromosomes. When they come together to make a new baby, she has the correct number of 46, 2 homologs of each type. 4. Mitosis is the process of cell division occurring when a diploid cell copies its chromosomes exactly to form another diploid cell. a. Mitosis allows growth, healing or replacement of damage to the body, or, for single celled creatures, population growth. b. Mitosis can also allow asexual reproduction. Many small animals and most plants can reproduce asexually, forming genetically identical clones of the parent. c. The two daughter cells produced by mitosis should be genetically identical unless there has been a mutation in the DNA. C. Mitosis is part of the cell cycle, and is divided into 5 stages. 1. The cell cycle is the life cycle of the cell: cells are born (by division), grow, and then reproduce themselves in another cell division. a. Cells can also die, of course, and sometimes the body kills its own cells by the process of apoptosis. 2. Interphase is the time between divisions when the cell grows and carries out its normal activities, including copying its DNA in preparation for the next division. Chromosomes are not visible under the microscope; the DNA is spread out so it can be used to make protein. Cells spend most of their lives in interphase. a. Interphase is subdivided into G1, S, and G2 phases. b. During G1 and G2 phases the cell grows and prepares for division. c. During S (synthesis) phase, each chromosome is copied by DNA replication and forms a pair of sister chromatids. Sister chromatids are two identical chromosomes, originating from a single double helix (remember DNA replication). They are stuck together during the process of copying and remain stuck together at the centromere throughout the first part of mitosis. d. DNA molecules can be several meters long but they are very thin. Sister chromatids are notvisible during interphase because the DNA is too thin. 3. In prophase the chromosomes become tightly wound up, or condensed, making them large enough to see under the microscope. The nuclear membrane which separates the nucleus from the rest of the cell disintegrates, and a new structure called the spindle is built to separate the sister chromatids. 4. In metaphase the chromosomes attach to the spindle and line up in the center of the cell. In each pair of sister chromatids, one attaches to one end of the spindle and the other to the oppositeend. 5. In anaphase the sister chromatids come apart, and each is pulled by the spindle to its end of thecell. A group of chromosomes forms at each end of the spindle. 6. Finally, in telophase, a new nucleus forms around each group of chromosomes, and the 2spindle disappears. Now we have one cell with two identical nuclei. 7. Cytokinesis is the division of the cell into two diploid cells, each containing its own nucleus. D. Normally, cells divide when they get a signal from the body; the rate and location of cell division is tightly controlled in animals. 1. Cells which stop responding to cell cycle controls become cancerous. What causes cancer?I. Cancer: a disease that results when mitosis is uncontrolled. A. Normal cells can become genetically transformed into cancer cells with very different ap-pearance and properties. 1. This occurs due to mutation, a random change in the cell's DNA. a. Since the DNA is changed, all descendants of the original cancer cell are also cancer cells. 2. Normal cells have a limited lifespan and divide only a certain number of times before they die. a. Cancer cells lose these limits. They will divide indefinitely as long as nutrients are sup-plied and wastes removed. 3. Cancer cells transport nutrients in faster than normal cells, diverting nutrients away from normal growth. 4. Normal cells show contact inhibition: they stop dividing when they contact other cells on allsides. When a cut heals, for example, cells divide until the wound is covered over with skin and then they stop. a. Cancer cells do not respect contact inhibition: they continue to divide even when sur-rounded by other cells, piling up on top of one another to form solid tumors. 5. Normal cells show anchorage dependence. They are attached to their neighbors, they commu-nicate with one another and they do not get up and move to new locations. a. Cancer cells can attach and detach from their neighbors. When detached, they cannot send or receive communications. b. They may also develop the ability to migrate within the body to a new location. B. There are