Mitosis
Thirteen colored pencils are needed for this page. Which colors you use don't matter, just be sure to use the same color for each object throughout the page.
Chromatin is named for the deep color it takes when cells are stained. The name comes from the Greek word "chromos", meaning color. Chromatin is seen during cell division to coil up into compact bundles called chromosomes as cells prepare to divide. In 1882 Walther Fleming worked out the details of the most common type of cell division which is called mitosos, from the Greek word "mitos" for thread, because of the threadlike appearance of the chromatin.
Although cell division is a continuous process, it is customary to divide it into four phases to make discussion easier. The period betwen divisions, when the cell is growing and carrying out its life functions, is called Interphase.
Color the heading Interphase at the upper right. Then color the headings Cell and Nucleus and titles A, B, D, E, and F. Color the cell beside the "interphase" heading.
During Interphase, the nucleus is surrounded by the nuclear envelope, and the chromatin is in the form of numerous loose threads. In cells of animals and primitive plants, a pair of centrioles is located in the cytoplasm just outside the nucleus. This coloring page illustrates division of such a centriole-containing cell.
Color the heading Prophase, all remaining titles, and the two prophase cells, one above and one below the Prophase heading.
Mitosis begins with prophase, in which the chromatin coils up and condenses into compace structures called chromosomes. Two prophase cells are shown, one early and one late, to emphasize the continuous nature of the process. As the chromosomes become shorter and thicker, it becomes clear that each one is made up of two subunits, which we call chromatids. If centrioles are present, a second pair of centrioles is synthesized during Interphase, and a starlike array of microtubules called an aster forms around the centrioles. As prophase proceeds, the two pairs of centrioles move toward opposite sides of the cell, each with its own aster. During this migration, numerous additional microtubules are assembled between the centrioles to form the spindle apparatus, which is so named because of its similarity to the spindle of a spinning wheel. Many microfilaments of actin (a muscle protein) become associated with the microtubules in the spindle. Any nucleoli present gradually become smaller and disappear. Eventually the asters arrive at opposite ends of the cell, and the spindle apparatus extends along one side of the nucleus. The nuclear envelope then disintegrates, marking the generally accepted end of Prophase. (Cells without centrioles do not form asters but do form a very similar spindle, which is known as an anastral spindle (Latin meaning "without".)
Color the heading Metaphase and the structures in the two metaphase cells, one above and one below the heading.
In the portion of mitosis designated as Metaphase, the spindle apparatus moves into the area of the nucleus. As it does so, the chromosomes move to the center of the spindle. Each chromosome attaches by a specialized portion (centromere) to a different bundle of spindle microtutules. In animals and seed plants, virtually all the cells have their chromosomes in homologous ("same-proportioned") pairs. This is referred to as the "diploid" condition. Almost every cell in the organism is diploid, except for the gametes or "sex cells". Gametes are "haploid", having only one chromosome of each pair. The number, size, and shape of the chromosomes is constant for any given species. Humans have 23 pairs of chromosomes in regular body cells; other species have chromosome numbers ranging from one pair to more than 200 pairs.
Color the heading Anaphase and Telophase and the corresponding cell structures. Then color the two daughter cells in the upper left corner.
In Anaphase, the chromatids of each chromosome separate to form two daughter chromosomes. The spindle tubules pull these daughter chromosomes to opposite sides of the cell so that each end of the daughter cells has an identical set. In Telophase, the spindle dissolves, the chromosomes uncoil and become a diffuse chromatin network again, and the nucleolus and nuclear envelope reappear. In a process called "cytokinesis", the cytoplasm is then divided to form two separate cells, each surrounded by its own membrane as illustrated at the upper left.
On another piece of paper, write one complete sentence to answer each of these questions.
- What does the Greek word "chromos" mean?
- In what year did Walter Fleming work out the details for mitosis?
- What form does the chromatin take in the nucleus during Interphase?
- In what phase of mitosis do chromosomes form?
- What name is given to the two subunits of a chromosome?
- Actin is what type of protein?
- What does homologous mean?
- Which cells in an organism have a "haploid" number of chromosomes?
- How many pairs of chromosomes are found in human body cells?
- What is the process called by which cytoplasm divides to form two separate cells?