CELL DIVISION PDF

4: HOW CELLS DIVIDE (MITOTIC CELL DIVISION) Rosanna Hartline West Hills College Lemoore CHAPTER OVERVIEW 4: How Cells Divide (Mitotic Cell Division) 4.1: Introduction to Cell Division 4.2: The Life of a Cell 4.3: Mitotic Cell Division- Division of the Nucleus (Mitosis) + Division of the Cytoplasm (Cytokinesis) 4.4: Uncontrolled Cell Divisions Create Tumors including Cancers 4.5: Laboratory Activities and Assignment 4.6: Collaborative Study Activity This page titled 4: How Cells Divide (Mitotic Cell Division) is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Rosanna Hartline. 1 4.1: Introduction to Cell Division Introduction to Cell Division Cells divide sometimes. This means that one cell splits into two cells. Humans would not exist without cell division. Every human starts life as one single cell, the result of egg and sperm fusing during fertilization. Then, as the human develops, a series of cell divisions occurs to make an embryo. One cell becomes two cells, two cells divide to produce four cells, four cells divide to produce eight cells, eight cells divide to produce sixteen cells, and so on. By the time a human is a fully grown adult, the human is composed of trillions of cells! Cell division does not end when a human is an adult since cell division is necessary to repair injuries and to replace old and worn out cells. Cells divide in humans for a variety of reasons including: embryonic development growth (infant --> child --> adolescent --> young adult --> adult) regeneration of dead and worn out cells repair of injuries (e.g. broken bone, broken skin, etc.) cell differentiation (cells change from stem cells to specific cell types) abnormal cell division (benign tumors; cancers) Another reason cells divide is to produce gametes, specialized sex cells that produce offspring (egg/ovum and sperm/spermatozoa). Although production of gametes requires cell division, the process of producing gametes is distinctly different from the type of cell division discussed in this chapter. See Chapter 21: Reproductive Systems to learn about cell division for gamete production (meiosis). Attributions "Mitotic Prophase" by LadyofHats is in the Public Domain "Mitotic Cytokinesis" by LadyofHats is in the Public Domain This page titled 4.1: Introduction to Cell Division is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Rosanna Hartline. 4.1.1 https://bio.libretexts.org/@go/page/53559 4.2: The Life of a Cell The Life of a Cell Cells go through different phases during their lives. These phases may involve preparing for cell division, or they may be in a phase where they are not moving toward a cell division. The sequence of phases or stages a cell goes through during its life is known as the cell cycle. Above: This diagram summarizes the life phases a cell goes through (the cell cycle). The abbreviations are as follows: I= interphase, G1 = G1 phase, S = S phase, G2 = G2 phase, G0 = G0 phase, and M = mitotic cell division. The outer circle shows that G1, G0, S, and G2 phases are all considered part of interphase. The inner circle shows the specific phases occurring during interphase. At the end of mitotic cell division, the cell divides into two. Both cells continue in the cell cycle after division - meaning that both cells are in the G1 phase after completing mitotic cell division. 4.2.1 https://bio.libretexts.org/@go/page/53560 The bulk of the cell's life in the cell cycle is spent in the “living phase”, known as interphase, a phase when a cell is not dividing. The cell might not be progressing toward a cell division at all - a phase known as G0 phase where cells do not move through the other stages of interphase preceding a cell division, but these cells typically are conducting normal cellular processes (undergoing metabolic reactions, conducting gene expression, responding to their environmental conditions etc.). If a cell in interphase is progressing toward cell division, then interphase involves normal cellular processes as well as three stages that prepare the cell for division. Preparation for cell division occurs in three phases occurring in the following order: G1 phase, S phase, and G2 phase: G1 phase: a phase of growth when the cell is accumulating resources to live and grow. After attaining a certain size and having amassed enough raw materials, a checkpoint is reached where the cell uses biochemical markers to decide if the next phase should be entered. S phase: a phase when metabolism is shifted towards the replication (or synthesis) of the genetic material (DNA replication). During S phase, the amount of DNA in the nucleus is doubled and copied exactly in preparation for cell division. Before S phase, the chromosomes exist as single chromatids. At the end of S phase, each chromosome consists of two identical sister chromatids (identical twin sister chromatids) attached to each other at a centromere. These identical sister chromatids are separated from each during the cell division process to produce two genetically identical cells at the end of cell division. G2 phase: a phase of growth and final preparation before the cell division process begins. Another checkpoint takes place at the end of G2 to ensure the fidelity of the replicated DNA and to re- establish the success of the cell’s capacity to divide in the environment. If conditions are favorable, the cell continues on to mitotic cell division. 4.2.2 https://bio.libretexts.org/@go/page/53560 Above: The diagram and chromosome images above show the distinctions between single chromatids and two identical sister chromatids attached at a centromere. Please note that this figure shows the DNA in these chromatids as condensed (the DNA is tightly coiled and organized into the structures shown above). Throughout interphase, the DNA is decondensed (loose) in the nucleus and cannot be observed in this condensed structure until mitotic cell division begins. Attributions "BIOL 250 Human Anatomy Lab Manual SU 19" by Yancy Aquino, Skyline College is licensed under CC BY-NC-SA 4.0 "Biology 2e" by Mary Ann Clark, Matthew Douglas, Jung Choi, OpenStax is licensed under CC BY-NC 4.0 "Cell Cycle 3-3" by Zephyris is licensed under CC BY-SA 3.0 / A derivative from the original work "SisterChromatid1" by Ascendinglotus2 is licensed under CC BY-SA 3.0 "UCSC human chromosome colours" by HYanWong is in the Public Domain, CC0 This page titled 4.2: The Life of a Cell is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Rosanna Hartline. 4.2.3 https://bio.libretexts.org/@go/page/53560 4.3: Mitotic Cell Division- Division of the Nucleus (Mitosis) + Division of the Cytoplasm (Cytokinesis) Mitotic Cell Division - Division of the Nucleus (Mitosis) + Division of the Cytoplasm (Cytokinesis) Human cells divide for embryonic development, growth of the human, injury repair, tumor and cancer development and spread, cell regeneration, and cell differentiation by a process called mitotic cell division. The word "mitotic" in "mitotic cell division" refers to the fact that mitosis, division of the nucleus, is a part of the entire cell division process. After mitosis is complete, the cell is still a single cell, but now the DNA has been divided into two nuclei, with each nucleus containing a set of DNA (chromatids) identical to the other nucleus. Producing genetically identical nuclei is possible because the cell separates the sister chromatids from each other during mitosis and packages one chromatid of each pair of identical sister chromatids into a separate nucleus. Mitotic cell division is only complete after the cell completely divides into two cells. After mitosis is complete, the cell with two nuclei undergoes cytokinesis to divide the cytoplasm, thereby completing mitotic cell division. Cells proceeding through the steps of mitotic cell division have a lot going on. DNA condenses at the beginning and decondenses at the end, the nucleus breaks down and then reforms as two nuclei, sister chromatids are separated into two separate nuclei, the chromatids are moved around, organized, and pulled apart by microtubules, and the entire cell splits in a way that 1 nucleus ends up in each daughter cell. To better understand and describe the phases of mitotic cell division, mitosis is broken up into the following phases: 1. prophase 2. prometaphase 3. metaphase 4. anaphase 5. telophase Cells leaving the G2 phase of the cell cycle enter prophase first, the first stage of mitosis. The last phase of mitosis is telophase where the cell contains two separate nuclei. Cytokinesis follows telophase to create two separate cells. Examine the table below to investigate the appearance of a cell in each phase of mitosis and the major events occurring in each phase. Pay special attention to the chromatids through this process (shown as orange/red Xs representing sister chromatids, as single red lines in anaphase representing single chromatids, and as orange dots in prophase and telophase representing decondensed DNA) as well as the nuclear envelope (shown as a dark green circle - when this line is dashed it indicates the envelope is either breaking down or forming), the microtubules aka mitotic spindle (shown as blue lines) that move chromatids around the cell, and centrosomes (shown as a pair of orange rectangles) that organize the microtubules: Phase of Mitosis Major Events of this Phase prophase Chromatids condense and become visible as Xs with a microscope Spindle fibers emerge from the centrosomes Nuclear envelope breaks down Nucleolus disappears 4.3.1 https://bio.libretexts.org/@go/page/53561 Phase of Mitosis Major Events of this Phase prometaphase Chromatids continue to condense Mitotic spindle microtubules attach to the chromatids Centrosomes move toward opposite poles of the cell metaphase Mitotic spindle is fully developed Centrosomes are at opposite poles of the cell Chromatids are lined up in the center of the cell (also known as the metaphase plate) Each sister chromatid is attached to a spindle fiber originating from opposite poles anaphase Sister chromatids (now called "chromatids" or "chromosomes" since the sister chromatids are separated) are pulled toward opposite poles of the cell The cell elongates due to action of the spindle fibers telophase The single chromatids arrive at opposite poles of the cell Nuclear envelope materials surround the two sets of chromatids and begins to assemble Chromatids begin to decondense The mitotic spindle begins to break down 4.3.2 https://bio.libretexts.org/@go/page/53561 After telophase is complete, mitosis is complete since the nucleus has now divided into two identical nuclei. Cytokinesis follows the end of mitosis to complete mitotic cell division: Phase of Mitotic Cell Division Major Events of this Phase cytokinesis A contractile ring of actin filaments pulls the equator of the cell inward, forming a fissure (this fissure is called a cleavage furrow) The cleavage furrow continues to deepen as the actin ring continues to get smaller and eventually the membrane is cleaved into to two Two daughter cells are produced These daughter cells begin their lives in G1 phase of interphase Although the events of mitotic cell division are separated into phases, it is analogous to breaking up an entire day into morning, afternoon, evening, and night - it is all a part of the same day, but we describe the parts differently. As such mitotic cell division is a fluid process where one stage evolves into the next. To see an animation of how mitotic cell division proceeds in a cell, watch this video. The length of the cell cycle is highly variable, even within the cells of a single organism. In humans, the frequency of cell turnover ranges from a few hours in early embryonic development, to an average of two to five days for epithelial cells, and to an entire human lifetime spent in G0 by specialized cells, such as cortical neurons or cardiac muscle cells. There is also variation in the time that a cell spends in each phase of the cell cycle. When fast-dividing mammalian cells are grown in culture (outside the body under optimal growing conditions), the length of the cycle is about 24 hours. In rapidly dividing human cells with a 24-hour cell cycle, the G1 phase lasts approximately nine hours, the S phase lasts 10 hours, the G2 phase lasts about four and one-half hours, and the M phase lasts approximately one-half hour. In early embryos of fruit flies, the cell cycle is completed in about eight minutes. The timing of events in the cell cycle is controlled by mechanisms that are both internal and external to the cell. Attributions "BIOL 250 Human Anatomy Lab Manual SU 19" by Yancy Aquino, Skyline College is licensed under CC BY-NC-SA 4.0 "Biology 2e" by Mary Ann Clark, Matthew Douglas, Jung Choi, OpenStax is licensed under CC BY-NC 4.0 "Mitotic Prophase" by LadyofHats is in the Public Domain "Mitotic Prometaphase" by LadyofHats is in the Public Domain "Mitotic Metaphase" by LadyofHats is in the Public Domain "Mitotic Anaphase" by LadyofHats is in the Public Domain "Mitotic Telophase" by LadyofHats is in the Public Domain "Mitotic Cytokinesis" by LadyofHats is in the Public Domain This page titled 4.3: Mitotic Cell Division- Division of the Nucleus (Mitosis) + Division of the Cytoplasm (Cytokinesis) is shared under a CC BY- NC-SA 4.0 license and was authored, remixed, and/or curated by Rosanna Hartline. 4.3.3 https://bio.libretexts.org/@go/page/53561 4.4: Uncontrolled Cell Divisions Create Tumors including Cancers Uncontrolled Cell Divisions Create Tumors including Cancers Tumors, including cancers, are caused by abnormal cells that multiply continuously. If the abnormal cells continue to divide unstopped, they can damage the tissues around them, spread to other parts of the body (malignancy), and even result in death. In healthy cells, the tight regulation mechanisms of the cell cycle prevent this from happening (cell cycle checkpoints), while failures of cell cycle control can cause unwanted and excessive cell division. Failures of cell cycle control may be caused by inherited genetic abnormalities (genetic predispositions) that compromise the function of certain cell cycle “stop” and “go” signals. Cell cycle checkpoints may also be compromised due to exposures to environmental factors that mutate cellular DNA causing dysfunction in those "stop" and "go" signals controlling the cell cycle. Often, a combination of both genetic predisposition and environmental factors lead to cancer. Environmental factors causing DNA mutations that may lead to cancers can include: exposures to mutagenic chemicals (e.g. chemicals in cigarette smoke, pollutants, etc.) radiation (e.g. X-rays, ultraviolet light) some viruses (e.g. human papilloma virus [HPV]) Above: Light microscope image of a tissue cross-section from a patient with a type of basal cell cancer. The growth of abnormal cells is bracketed on either side, but the overall shape of the cancer tissue is roughly circular. The process of a cell escaping its normal control system and becoming cancerous may actually happen throughout the body quite frequently. Fortunately, certain cells of the immune system are capable of recognizing cells that have become cancerous and destroying them. However, in certain cases the cancerous cells remain undetected and continue to proliferate. If the resulting tumor does not pose a threat to surrounding tissues, it is said to be benign and can usually be easily removed. If capable of causing 4.4.1 https://bio.libretexts.org/@go/page/53562 damage to surrounding tissues and spreading through the blood and/or lymph, the tumor is considered malignant and the patient is diagnosed with cancer. Attributions "Anatomy and Physiology" by J. Gordon Betts et al., OpenStax is licensed under CC BY 4.0 "Biology 2e" by Mary Ann Clark, Matthew Douglas, Jung Choi, OpenStax is licensed under CC BY-NC 4.0 "Palisading in basal cell cancer (original)" by Mikael Häggström, M.D. is in the Public Domain, CC0 This page titled 4.4: Uncontrolled Cell Divisions Create Tumors including Cancers is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Rosanna Hartline. 4.4.2 https://bio.libretexts.org/@go/page/53562 4.5: Laboratory Activities and Assignment Laboratory Activities and Assignment Introduction In these laboratory activities, you will be examining real cells that have been frozen in time in the midst of undergoing the various phases of the cell cycle. To better examine the many cell cycle stages that occur with real cells, we use cells that are undergoing a high amount of cell division. One great source of rapidly dividing animal cells is in early embryonic development. A blastula is a ball of cells in an early embryonic phase and is continuing to undergo rapid cell divisions. After egg and sperm meet, the fertilized ovum rapidly begins to divide and will go through this blastula stage. Since we are interested in studying cell division in humans (a type animal), and it would be unethical to examine human blastula, fish blastula are commonly used. Real cells can look quite different than the illustrated versions of cells in their cell cycle stages. To assist with recognizing these stages, examine the table above showing images of real animal cells. A description of features that can be used to identify cells in each stage is also provided. Note that these microscope slides are prepared using stains that stain the DNA (chromosomes/chromatids) a color that makes it more obvious such as purple, blue, or pink. The images above have the DNA stained dark purple. Interphase Prophase Metaphase Anaphase Telophase Chromosomes are less confined in a Two round nuclei circle structure (nucleus breaking Chromosomes are condensed (can see Chromosomes are condensed Nucleus is present inside one cell down) individual thick strands) (can see individual thick Chromosomes are not Chromosomes are Chromosomes are condensed (can Chromosomes are roughly lined up in strands) condensed (cannot see not condensed see individual thick strands) a line Chromosomes are pulling individual thick strands) (cannot see Chromosomes are NOT in a line or Chromosomes are NOT pulling apart apart to opposite poles of the Only one nucleus present individual thick pulling apart to opposite poles of the to opposite poles of the cell cell strands) cell Quantify Cells in Each Cell Cycle Phase in a Fish Blastula Note: It is recommended students complete the Collaborative Study Activity for this chapter before beginning this section. This activity will better prepare students to identify the appearance of fish cells in each phase of the cell cycle. 1. Obtain a "fish blastula" or "fish mitosis" slide and setup a microscope. 2. Focus on a single blastula at low power and increase magnification incrementally, focusing at each power along the way. Do not skip objectives without re-centering and re-focusing the sample. 3. Carefully examine the blastula at 400x total magnification. 4. Count the number of cells in the entire blastula that are in interphase and record in the table below in the individual counts column. 5. Count the number of cells in the entire blastula that are in prophase and record in the table below in the individual counts column. 6. Count the number of cells in the entire blastula that are in metaphase and record in the table below in the individual counts column. 7. Count the number of cells in the entire blastula that are in anaphase and record in the table below in the individual counts column. 8. Count the number of cells in the entire blastula that are in telophase and record in the table below in the individual counts column. 9. Share your data with your instructor so they can compile class data. Analyze Fish Blastula Data to Estimate Relative Durations of Each Phase of the Cell Cycle In the table below, record individual and class data indicating the number and percentages of cells in each phase of the cell cycle in fish blastula. Individual Counts Class Counts # Cells % Cells Class # Cells Class % Cells 4.5.1 https://bio.libretexts.org/@go/page/53563 Individual Counts Class Counts Interphase Prophase Metaphase Anaphase Telophase Total Calculate the percentage of cells in each phase of the cell cycle: % cells = (cells in that stage ÷ total number of cells counted) x 100 1. Create a stacked bar graph presenting class % cells during the cell cycle for fish blastula cells. USE A RULER to make the graph neat and professional- looking. Include in the graph the following: Labels for the x-axis and y-axis: Y-axis numbered corresponding the percentage of cells observed. The bottom of the y-axis is 0% and the top line of the y-axis is 100%. Each line up the y-axis is a specific increment (as determined by you) increasing up the y-axis. Y-axis title to tell what the numbers mean: Percentage of cells in each stage. X-axis label to tell what the bar shows (Fish Blastula). Each of the two bars stretch from 0% to 100% but are divided into the stages of the cell cycle using different colors based on the % of cells in each stage. A key is needed to tell what each color shows. Bar sections should be colored in NEATLY so the graph looks professional. Title for the graph. Alternatively, Excel may be used to create a stacked bar graph or a pie chart. 4.5.2 https://bio.libretexts.org/@go/page/53563 2. Examine your graph. The percentage of cells observed in a specific stage the cell cycle is indicative of the length of time a cell requires for each stage (the greater the % cells, the longer the phase lasts during the cell cycle; the fewer the % cells, the shorter that phase is in the cycle cycle). Using your data, discuss the length of time each of the phases of the cell cycle lasts. Which is the longest phase? Which phase is the shortest? How do all the phases compare with each other? Additional Questions 1. Use the letters to match with the descriptions as appropriate. Some choices may be used more than once and some may not be used at all. ______ A phase when chromosomes line up in the center of the cell. ______ A phase when the nuclear envelope begins to dissolve. A. mitosis ______ A phase between cell divisions. B. interphase ______ A phase when chromosomes separate from one another. C. prophase ______ Nuclear division. D. homologous chromosomes ______ A phase when DNA replication occurs. E. telophase ______ A phase when the DNA decondenses. F. anaphase ______ Type of chromosomes that separate during mitosis. G. cytokinesis ______ Division of the cytoplasm to produce 2 separate cells. H. sister chromatids ______ A phase where the cell grows and organelles replicate. I. metaphase ______ A phase where DNA condenses. J. S phase ______ A process that produces sister chromatids. ______ A phase when the nuclear envelope reforms. 4.5.3 https://bio.libretexts.org/@go/page/53563 2. Label the images of stages of the cell cycle using the choices below: interphase prophase metaphase anaphase telophase cytokinesis Attributions Introduction "Mitosis (261 01) Pressed; root meristem of Vicia faba" by Doc. RNDr. Josef Reischig, CSc. is licensed under CC BY-SA 3.0 "Mitosis (261 02) Pressed; root meristem of Vicia faba (cells in prophase)" by Doc. RNDr. Josef Reischig, CSc. is licensed under CC BY-SA 3.0 "Mitosis (261 03) Pressed; root meristem of Vicia faba (cells in prophase, metaphase)" by Doc. RNDr. Josef Reischig, CSc. is licensed under CC BY-SA 3.0 "Mitosis (261 08) Pressed; root meristem of Vicia faba (cells in telophase)" by Doc. RNDr. Josef Reischig, CSc. is licensed under CC BY-SA 3.0 "Mitosis (261 10) Pressed; root meristem of Vicia faba (cells in anaphase, prophase)" by Doc. RNDr. Josef Reischig, CSc. is licensed under CC BY-SA 3.0 "PSM V84 D534 Facts and factors of development fig10" by Edwing Grant Conklin is in the Public Domain Analyze Fish Blastula Data to Estimate Relative Lengths of Each Phase of the Cell Cycle "Graph paper inch Letter" by László Németh is in the Public Domain, CC0 Additional Questions "Anatomy and Physiology I Lab" by Victoria Vidal is licensed under CC BY 4.0 This page titled 4.5: Laboratory Activities and Assignment is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Rosanna Hartline. 4.5.4 https://bio.libretexts.org/@go/page/53563 4.6: Collaborative Study Activity Collaborative Study Activity This activity works best with student pairs of two, but groups of four can be created and students work in pairs within those groups. Having groups of four is better if there is no supplemental instructor present to help quiz the students after they practice in their pairs. Students will access the flashcard deck linked below as described. In their pairs, students test each other using the flashcards until they have mastered the flashcard deck, at which point the student pair will request the instructor come test them on the deck. Flash Cards on a Mobile Device The flashcards deck can be accessed on mobile devices using the Cram.com app. To access the flashcard deck on a mobile device, click the appropriate link below to download the app and then click on the link above to access the flashcard deck. Students should save the flashcard deck in the app by hitting the heart button at the bottom of the screen to add it to their favorites. Download the Cram.com App: GooglePlay Apple App Store Identifying Phases of the Cell Cycle 1. Access the flashcard deck using the link: Human Anatomy Laboratory Manual (Hartline)-Chapter 4: Collaborative Study Activities-Mitotic Cell Division 2. Test your partner on the flashcard deck. 3. Have your partner test you on the flashcard deck. 4. When you and your partner have mastered the flashcard deck, request the assistance of your Instructor. They will test you using the flashcard deck and initial ONLY when you have successfully mastered the flashcard deck. Instructor: _______ Attributions "Mitosis (261 01) Pressed; root meristem of Vicia faba" by Doc. RNDr. Josef Reischig, CSc. is licensed under CC BY-SA 3.0 "Mitosis (261 02) Pressed; root meristem of Vicia faba (cells in prophase)" by Doc. RNDr. Josef Reischig, CSc. is licensed under CC BY-SA 3.0 "Mitosis (261 03) Pressed; root meristem of Vicia faba (cells in prophase, metaphase)" by Doc. RNDr. Josef Reischig, CSc. is licensed under CC BY-SA 3.0 "Mitosis (261 08) Pressed; root meristem of Vicia faba (cells in telophase)" by Doc. RNDr. Josef Reischig, CSc. is licensed under CC BY-SA 3.0 "Mitosis (261 10) Pressed; root meristem of Vicia faba (cells in anaphase, prophase)" by Doc. RNDr. Josef Reischig, CSc. is licensed under CC BY-SA 3.0 "Mitosis Stages" by Ali Zifan is licensed under CC BY-SA 4.0 "Mitotic Prophase" by LadyofHats is in the Public Domain "Mitotic Prometaphase" by LadyofHats is in the Public Domain "Mitotic Metaphase" by LadyofHats is in the Public Domain "Mitotic Anaphase" by LadyofHats is in the Public Domain "Mitotic Telophase" by LadyofHats is in the Public Domain "Mitotic Cytokinesis" by LadyofHats is in the Public Domain "SisterChromatid1" by Ascendinglotus2 is licensed under CC BY-SA 3.0 "UCSC human chromosome colours" by HYanWong is in the Public Domain, CC This page titled 4.6: Collaborative Study Activity is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Rosanna Hartline. 4.6.1 https://bio.libretexts.org/@go/page/53568

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