Mitosis PDF

Name: __________________________________ Section: _______________ Date: _________ MITOSIS A Quick Overview of Cell Division The genetic information of plants, animals and other eukaryotic organisms resides in several individual DNA molecules, or...

Name: __________________________________ Section: _______________ Date: _________ MITOSIS A Quick Overview of Cell Division The genetic information of plants, animals and other eukaryotic organisms resides in several individual DNA molecules, or chromosomes. For example, each human cell possesses 46 chromosomes, while each cell of an onion possesses 8 chromosomes. All cells must replicate their DNA when dividing. During DNA replication, the two strands of the DNA double helix separate, and for each original strand a new complementary strand is produced, yielding two identical DNA molecules. A process by which a parent cell divides into two or more daughter cells is called cell division. Cell division is a small part of the cell cycle. In normal eukaryotic cells, the type of cell division is known as mitosis. Another type of cell division is present in reproductive cells of eukaryotes and is known as meiosis. Cell cycle is mainly classified into two segments: M-phase and Interphase. Interphase is the longer period of cell division. During this phase the cell prepares for its next stage. Mitosis Mitosis refers to a type of cell division (cell cycle) through which the cell (parent cell) produces two identical daughter cells. Unlike Meiosis, which is also a type of cell division, mitosis results in the production of two diploid daughter cells. The two daughter cells contain the same number of chromosomes as the parent cell. Given that the process results in the proliferation of cells, it's important for general growth and replacement of damaged cells (e.g., the wound healing process). In general, mitosis occurs through several stages that include: Prophase (divided into prophase and prometaphase), Metaphase, Anaphase, & Telophase Onion Root Tip Mitosis Because of the rapid rate at which onion root tips grow as a result of rapid cell division, it's possible to observe and identify the different stages of mitosis. An onion has a total of 8 pairs of chromosomes. This is especially beneficial for this experiment given that fewer chromosomes are slightly easier to see when they condense. Laboratory Objectives Explain the process and stages of mitosis. Identify specimens of onion root to visualize all of the stages of mitosis. Apply an analytical technique by which the relative length of each stage of mitosis can be estimated. DUMAGUETE CITY, NEGROS ORIENTAL, 6200 PHILIPPINES +6335 420 1901 loc 425/426; [email protected] | www.su.edu.ph Experiment For this section, the experiment will be divided into two main parts. These include growing onion root tips. Growing fresh root tips is recommended given that older or dried roots may produce poor results. As mentioned, onion root tip cells divide rapidly as the roots elongate to absorb water and various minerals from the soil. For this reason, it's possible to identify different stages of cell division by mitosis based on chromosomal distribution. Requirements Uncut red onions Clear glass or plastic jars Clean water Toothpicks Masking tape Permanent markers Procedure 1. Pour clean water into the clean (and clear) glass/plastic jars - about three-quarters full. 2. Carefully place the onion bulbs in the glass/plastic jars so that only the lower surface of the onion comes in contact with the water. 3. In a case where the onions are too small, they can be supported using toothpick/splints. 4. Let the onions rest on water for 3-4 days - only the lower surface (base from which roots emerge) should be in contact with water. I. Illustrate the diagrammatic representations of this setup. II. Why use onion roots for viewing mitosis? _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ DUMAGUETE CITY, NEGROS ORIENTAL, 6200 PHILIPPINES +6335 420 1901 loc 425/426; [email protected] | www.su.edu.ph III. Observations and Inferences Timeline Observations Inferences After 24 hours After 48 hours After 36 hours Conclusions: IV. Illustrate the diagrammatic representations of the results and observations. In an actual laboratory set-up, under 10X magnification, students will be able to observe several single layers of cells. Depending on how well the slide was prepared, the cells are spread out without any overlapping or with very little overlapping. Some root cells have ceased dividing and are only increasing in size, whereas others have reached their final, mature size and function, and are said to be in the GO stage. Generally, a row of cells (single layer) may consist of between 2 and 5 cells. When viewed under the microscope, a properly prepared slide will yield the following results: The following is a diagrammatic representation of onion root tip cells under 10X magnification DUMAGUETE CITY, NEGROS ORIENTAL, 6200 PHILIPPINES +6335 420 1901 loc 425/426; [email protected] | www.su.edu.ph  MITOSIS AND THE CELL CYCLE INTERPHASE ∞ Cell that are actively dividing but not yet in mitosis are said to be in interphase, during which time the DNA is copied and the cell is otherwise preparing for replication. ∞ While this is not necessarily one of the main stages of mitosis, cells in this state can easily be identified by their prominent nucleoli. Diagrammatic representation of an onion root tip cell during interphase: DUMAGUETE CITY, NEGROS ORIENTAL, 6200 PHILIPPINES +6335 420 1901 loc 425/426; [email protected] | www.su.edu.ph  ∞ During interphase, also known as the resting stage, the chromatin is not tightly packed. This allows for DNA to be copied (replication) as the cell prepares for cell division. ∞ The DNA strands are uncoiled during interphase for transcription to occur. In this state, the DNA is said to be uncondensed. Here, this genetic material is also referred to as chromatin. Generally, interphase is divided into three main phases that include: ✓ G1 (First gap phase) - Characterized by cell growth and normal cellular activities ✓ S phase (Synthesis) - This is the phase in which DNA is replicated so that the DNA content is doubled ✓ G2 phase (second gap phase) - During this phase, the cell prepares for division THE STAGES OF MITOSIS (P.P.M.A.T.) PROPHASE ∞ During prophase, the chromosomes supercoil and the fibers of the spindle apparatus begin to form between centrosomes located at the pole of the cells. ∞ The nuclear membrane also disintegrates at this time, freeing the chromosomes into the surrounding cytoplasm. ∞ During this stage of mitosis, the nucleolus is still visible. However, the nucleus appears grainy due to chromosomal condensation. ∞ During prophase, condensed DNA and some proteins form the chromatids which join to become chromosomes (X-shaped). ∞ Sister chromatids, which contain the same genetic information, are attached at a region known as the centromere which gives the structure an X shape. ∞ The kinetochore, which is the site at which microtubules join the chromosomes is also located at the centromere. As the chromatins coil, it becomes increasingly compact which allows the chromosomes to become more visible when viewed under high magnification. ∞ It's also during prophase that spindle microtubules (mitotic spindle) start forming near the nucleus. The following is a diagrammatic representation of an onion root tip cell during prophase: DUMAGUETE CITY, NEGROS ORIENTAL, 6200 PHILIPPINES +6335 420 1901 loc 425/426; [email protected] | www.su.edu.ph PROMETAPHASE ∞ Prometaphase is the second stage of mitosis (it has also been referred to as late prophase). ∞ This stage is characterized by increased condensation of chromosomes as well as the breakdown of the nuclear envelope (nuclear membrane). ∞ The nuclear envelope, which consists of an inner and outer membrane, is stabilized by polymerization of Lamin proteins (the nuclear lamina). ∞ Polymerization of the Lamins and the consequent breakdown of filaments into Lamin dimers results in the disassembly of the nuclear membrane. ∞ This stage is also characterized by the development of kinetochore around the centromere. ∞ Spindle fibers (kinetochore microtubules) have also been shown to start developing during prometaphase and permeate through the disappearing membrane to attach to the chromosomes at the kinetochore. ∞. During prometaphase, some of the fibers attach to the centromere of each pair of sister chromatids and they begin to move toward the center of the cell. ∞ This stage of mitosis is important because chromosomes (sister chromatids) have to be released from the nuclear membrane in order to be separated in the next stage. METAPHASE ∞ In this stage of mitosis, chromosomes align along the equatorial plane of the cell (cell equator) so that the sister chromatids can be separated. ∞ During metaphase, chromosomes become more visible because of increased condensation as well as the fact that the nuclear envelope has disappeared. ∞ Given that the nuclear membrane completely disappears during metaphase, the chromosomes appear in the cytoplasm. ∞ The fully developed spindle fibers originating from the centrioles, located on opposite poles of the cell, attach to each of the sister chromatids which contribute to their alignment at the cell equator. ∞ Based on microscopic studies, spindle fibers (microtubules made of proteins) have been shown to be about 25nm in diameter. While they originate from the centrioles and extend to attach to the sister chromatids, they have also been shown to be constantly forming because they are continually broken down. DUMAGUETE CITY, NEGROS ORIENTAL, 6200 PHILIPPINES +6335 420 1901 loc 425/426; [email protected] | www.su.edu.ph  ∞ As new components (building blocks) are added on one end of the microtubules and removed from the other, it has been suggested that this causes the microtubules to pull the centrioles which in turn contributes to the alignment of the chromosomes. ∞ In late metaphase, the pulling actions of the microtubules, as well as the centrioles, result in the kinetochores (the region at which spindle fibers attach to the chromosomes) facing different directions. Diagrammatic representation of a cell during metaphase: ANAPHASE ∞ During anaphase, the chromosomes start separating and moving from the equatorial plate of the cell. ∞ At the end of this stage (late anaphase), the sister chromatids completely separate and reach the opposite poles of the cell. ∞ In this stage, it's also possible to clearly identify the chromatids given that the process occurs in the cytoplasm. ∞ Based on microscopic studies, sister chromatids have been shown to separate and move to the opposite poles of the cell at a rate of between 0.2 and 4 um per minute. Initially, polymerization and depolymerization of microtubules was thought to result in the separation and movement of chromatids to the opposite poles of the cell. ∞ As a result of the depolymerization process, microtubules shorten thus pulling apart the sister chromatids. As well, polymerization of some of the microtubules, those that extend from one pole of the cell to the other without attaching to the chromatids, causes them to grow in length thus pushing poles of the cell apart. ∞ Based on recent studies, however, it has become evident that separation of sister chromatids during anaphase is the result of the actions of enzyme seperase as well as shortening of microtubules. ∞ Here, the enzyme seperase has been shown to break down cohesin (a component of centromere that links sister chromatids). ∞ Following the separation of sister chromatids, through the breakdown of the protein cohesin, shortening of microtubules (kinetochore microtubules/spindle) pulls the chromatids to the opposite poles of the cell. Some of the other factors suggested to DUMAGUETE CITY, NEGROS ORIENTAL, 6200 PHILIPPINES +6335 420 1901 loc 425/426; [email protected] | www.su.edu.ph  contribute to the separation of sister chromatids include the pulling actions of astral microtubules (pulling the poles apart) while interpolar microtubules slide past each other. Diagrammatic representation of a cell during late anaphase: TELOPHASE ∞ Telophase is the fifth stage of mitosis characterized by several key events. ∞ These include arrival of the chromosomes at the opposite poles of the cell, gradual breakdown of the spindle fibers as well as development of nuclear envelopes around each set of chromosomes (at the opposite ends/poles of the cells). ∞ As nuclear envelopes develop around each set of chromosomes located at the opposite poles of the cell, two nuclei are formed in the cell. The DNA also starts to uncondensed so that genetic material can be copied later. ∞ Given that the spindle fibers are no longer required, they start to disassemble (break down) in early telophase and continue to do so in late telophase. Diagrammatic representation of a cell during telophase (late telophase): DUMAGUETE CITY, NEGROS ORIENTAL, 6200 PHILIPPINES +6335 420 1901 loc 425/426; [email protected] | www.su.edu.ph CYTOKINESIS ∞ Cytokinesis refers to the process through which the cytoplasm separates as the cell divides into two identical daughter cells. Unlike animal cells, plant cells have a rigid cell wall that prevents the cell from easily pinching apart to form two identical daughter cells. ∞ For this reason, the process of cytokinesis is different in these cells (plant cells). During late telophase and early cytokinesis, carbohydrate filled vesicles are released by the Golgi bodies and occupy the equator region of the cell. The vesicles continue fusing to form the cell plate which divided the cell int :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: REVIEW QUESTIONS 1. Describe the different forms that DNA takes before and during cell division in a eukaryotic cell. _____________________________________________________________________________________ _____________________________________________________________________________________ 2. Identify the four phases of mitosis in an animal cell, and summarize what happens during each phase. _____________________________________________________________________________________ _____________________________________________________________________________________ 3. Explain what happens during cytokinesis in an animal cell. _____________________________________________________________________________________ _____________________________________________________________________________________ 4. What are the main differences between mitosis and cytokinesis? _____________________________________________________________________________________ _____________________________________________________________________________________ 5. The familiar X-shaped chromosome represents: A. How DNA always looks in eukaryotic cells B. How DNA in eukaryotic cells looks once it is replicated and the cell is about to divide C. Female sex chromosomes only D. How DNA appears immediately after cytokinesis DUMAGUETE CITY, NEGROS ORIENTAL, 6200 PHILIPPINES +6335 420 1901 loc 425/426; [email protected] | www.su.edu.ph 6. Which of the following is not part of a chromosome in eukaryotic cells? A. Centriole B. Centromere C. Chromatid D. DNA 7. What do you think would happen if the sister chromatids of one of the chromosomes did not separate during mitosis? _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ 8. Put the following processes in order of when they occur during cell division. Assign number 1 as first to 5 as last. ____ separation of sister chromatids ____ DNA replication ____ cytokinesis ____ lining up of chromosomes in the center of the cell ____ condensation and coiling of DNA into a chromosome 9. Why do you think the nuclear envelope breaks down at the start of mitosis? _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ 10. What are the fibers made of microtubules that attach to the centromeres during mitosis are called? _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ 11. True or False. Chromosomes begin to uncoil during anaphase. _______ 12. True or False. During cytokinesis in animal cells, sister chromatids line up along the equator of the cell. _______ 13. True or False. After mitosis, the result is typically two daughter cells with identical DNA to each other. _______ 14. How does cytokinesis differ in plant and animal cells? _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ DUMAGUETE CITY, NEGROS ORIENTAL, 6200 PHILIPPINES +6335 420 1901 loc 425/426; [email protected] | www.su.edu.ph  15. Identify the stages of division in onion root cells in the photo below and count the number the number of cells in each stage by writing the tally marks in the box. Prophase Prometaphase Metaphase Anaphase Telophase 16. 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. mitosis ______ A phase when chromosomes line up in the center of the cell. B. interphase ______ A phase when the nuclear envelope begins to dissolve. C. prophase ______ A phase between cell divisions. D. homologous chromosomes ______ A phase when chromosomes separate from one another. E. telophase ______ Nuclear division. F. anaphase ______ A phase when DNA replication occurs. G. cytokinesis ______ A phase when the DNA decondenses. H. sister chromatids ______ Type of chromosomes that separate during mitosis. I. metaphase ______ Division of the cytoplasm to produce 2 separate cells. J. S phase ______ Division of the cytoplasm to produce 2 separate cells. ______ A phase where the cell grows and organelles replicate. ______ A phase where DNA condenses. ______ A process that produces sister chromatids. ______ A phase when the nuclear envelope reforms. DUMAGUETE CITY, NEGROS ORIENTAL, 6200 PHILIPPINES +6335 420 1901 loc 425/426; [email protected] | www.su.edu.ph 17. Identify the different stages of cell division shown in the photos below. A. _______________ B. _______________ C. _______________ D. _______________ E. _______________ F. _______________ G. _______________ H. _______________ I. _______________ J. _______________ A. _______________ B. _______________ C. _______________ D. _______________ E. _______________ F. _______________ Cooper GM. (2000). The Cell: A Molecular Approach. 2nd edition. Donald, B. and Richard, J. (2018). Cell Division. An Atlas of Comparative Vertebrate Histology. Lian, Y. and Chirop, M. (2016). Functional Cell Biology. Encyclopedia of Cell Biology. Lodish H, Berk A, and Zipursky SL, et al. (2000). Microtubule Dynamics and Motor Proteins during Mitosis: Molecular Cell Biology. 4th edition. Links https://employees.csbsju.edu/ssaupe/biol115/cell_division.htm https://www.yourgenome.org/facts/what-is-mitosis https://www.nature.com/scitable/topicpage/chromosomes-14121320/#:~:text=During%20interphase%20(1)%2C%20chromatin,mitosis%20(2%2D5) https://www.weber.edu/wsuimages/jonclark/PDFs/Genetics/Mitosis.pdf https://www.microscopemaster.com/onion-root-tip-mitosis.html#gallery[pagegallery]/2/ Prepared by: Jill Hanah C. Palafox, RN, LPT 2024 DUMAGUETE CITY, NEGROS ORIENTAL, 6200 PHILIPPINES +6335 420 1901 loc 425/426; [email protected] | www.su.edu.ph