Transcript Mitosis
Unit #6 Cell Division: Mitosis Do we get larger because our cells increase in size or because we produce more of them? The cells of an adult are no larger than the cells of a child – there are just more of them! Why do cells divide? A cell cannot grow forever. Eventually it must divide. There are three reasons why cell growth is limited: • The cell’s DNA would not be able to meet the needs of large cells • Nutrients would not enter fast enough • Wastes would not exit fast enough Therefore, a cell divides into two identical cells to prevent it from becoming too large. Before cell division, a cell copies all of its DNA so both new cells have a complete set of genetic information. Chromosomes Chromosomes In eukaryotic cells, the genetic information that is passed on from one generation of cells to the next is carried by chromosomes. Chromosomes- are made up of DNA and holds the cell’s genetic information (genes). The cells of every organism have a specific number of chromosomes. • Fruit fly cells have 8 chromosomes • Carrot cells have 18 chromosomes. • Human cells have 46 chromosomes • Cows have 60 chromosomes Well before cell division, each chromosome is replicated Because of this, when they become visible at the beginning of cell division, each chromosome consists of two identical “sister” chromatids as shown below. Checkpoint The sister chromatids are identical because 1. one is a copy of the other. 2. they are both copies of a third chromatid that came before them. 3. they are both made of DNA and protein. Biologists divide the events of mitosis into Four phases: telophase cytokinesis G2: cell growth 1. Prophase G1: cell growth and differentiation mitotic cell division 2. Metaphase 3. Anaphase 4. Telophase S: synthesis of DNA; chromosomes are duplicated InterphaseResting Depending on the type of cell, the four phases of mitosis may last anywhere from a few minutes to several days. Remember • Before Mitosis a cell copies all of its DNA (Chromosomes ) so both new cells have a complete set of genetic information. Prophase • chromosomes become visible (condense) • nuclear envelope disappears • centrioles move to opposite sides of the cell. Plant cells do not have centrioles • spindle begins to form and attaches to centromere Checkpoint The function of the spindle is to a. break down the nuclear envelope. b. help form a new nuclear envelope c. help separate the chromosomes. Metaphase • chromosomes line up at the middle of the cell Anaphase • Sister chromatids separate at centromere into individual chromosomes • Chromosomes move toward poles of cell • Anaphase ends when chromosomes stop moving Check Point • What happens during anaphase? A. The chromosomes become visible. B. The chromosomes line up across the center of the cell. C. The sister chromatids separate. Telophase • Chromosomes become less condensed • Nuclear envelope forms around each cluster of chromosomes • Spindle disappears • Start of cytokinesis Video Mitosis is complete. However, cell division is not complete. Cytokinesis • occurs during telophase • cytoplasm divides Video In most animal cells, the cell membrane is drawn inward until the cytoplasm is pinched into two nearly equal parts In plants, a structure known as the cell plate forms between the two cells. Mitosis Animation Mitosis Review 1. Name the main events of the cell cycle. 2. Describe what happens during each of the four phases of mitosis. 3. What are chromosomes made of? 4. How is cytokinesis in plant cells similar to cytokinesis in animal cells? How is it different? Cleavage Cleavage is the name for the process of mitosis that occurs in cells that forms a developing embryo. Cleavage involves all the steps of mitosis, but after cell division, it quickly goes through mitosis again. This results in a mass of many small undifferentiated cells. These cells will lead to the development of an embryo from a fertilized egg gastrula Once a gastrula forms, cells start to arrange themselves in different layers. The different layers of cells will differentiate into different tissues, which will form organs. When the different tissues form, the mass of cells is called an embryo. Differentiation • In most multicellular organisms, not all cells are alike. For example, cells that make up the human skin are different from cells that make up the inner organs. Yet, all of the different cell types in the human body are all derived from a single fertilized egg cell through differentiation. Cellular differentiation is a concept from developmental biology describing the process by which cells acquire a "type". 1. The outer layer of cells is called the ectoderm. It will differentiate into nerve cells and skin cells 2. The middle layer of cells is called the mesoderm. It will differentiate into cells that form the muscular system, circulatory system, excretory system and endocrine system 3. The inner layer of cells is called the endoderm. It will differentiate into cells that form the digestive system, pancreas, liver and lungs What is cancer? • Uncontrollable cell division resulting in a malignant and invasive growth or tumor. • If untreated -Metastasis is the spread of cancer from its primary site to other places in the body (e.g., brain, liver).