MITOSIS AND THE CELL CYCLE PowerPoint Notes

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1 1 Name: Date: MITOSIS AND THE CELL CYCLE PowerPoint Notes THE FUNCTIONS OF CELL DIVISION 1. Cell division is vital for all. living organisms This is the only process that can create. new cells 2. Cell Division always involves two main processes: 1) The division of the nuclear contents. 2) The division of the cytoplasmic contents. 3. There are FIVE main functions of cell division: 1) Asexual reproduction for cellular uni organisms. Prokaryotes (like bacteria) as well as unicellular protists (like paramecium) reproduce asexually by a type of cell division called. binary fission Fig.1 Binary fission in bacteria. 2) Asexual reproduction for cellular multi organisms. Organisms like hydra (an underwater animal) undergo cell division to produce growths (buds) from their bodies which eventually fall off and become cloned offspring. This process is called. budding Autotomy is when an organism performs a self-amputation of one of its body parts. Some starfish can autotomize their arms which will undergo cell division to regenerate into cloned offspring. Some plants reproduce without seeds or spores through asexual Fig.2 Autotomy of arms in some starfish.. vegetative reproduction One method of doing this is to undergo cell division to produce runners which are extensions from the parent plant that contain attached cloned offspring. Two types of plants that do this are. spider plants and strawberry plants 3) Sexual reproduction in cellular multi organisms. In sexual reproduction, cell division is required for two reasons: 1) to make gametes like sperm and. eggs 2) to allow the multiple divisions needed to create a multicellular organism.

2 2 4) Growth and development of a multi cellular organism. To reach adult size and attain, adult structures many organisms have to continue to perform cell division even after all essential body parts have formed. Fig.3 Male Human Growth and Development. 5) Repair and maintenance of a cellular multi organism. Give three examples: 1) Repair of broken bones. 2) Repair skin from sunburn. 3) Replace dead red blood cells. 4. Except during the creation of, gametes cell division results in daughter cells that are genetically identical to each other and to the parent. cell To create identical daughter cells, this type of cell division must involve DNA replication and a process called mitosis which involves the sorting and dividing of the DNA into two equal halves. Mitosis is a part of the. cell cycle THE CELL CYCLE Fig.4 Cell Division. The Cell Cycle 5. Cell Cycle: This represents the processes that occur between one cell division and the next cell division in a cell s life. 6. This involves three main stages and can be represented in a pie chart: 1) interphase 2) mitosis 3) cytokinesis The size of each pie slice roughly represents how much time a cell stays in each part of the cell cycle, but there are great variations depending on the type of cell. mitosis interphase Fig.5 The Cell Cycle

3 3 Interphase 7. Interphase: The cell spends most of its life here performing its specialized functions and then prepares for cell division when the time comes. 8. Interphase can be broken down into three stages: 1) G1 Phase (Gap 1): The cell grows after cell division to reach full size (it may double in size). The cell performs its specialized function depending on what type of cell it is. Fig.6 Various Cell Types This is the longest part of the cell cycle for most cells except for fast dividing embryonic cells and cancer cells. Once organisms reach adulthood, some of their cells will never divide again. These cells stop progressing through the cell cycle and go into G0 (Gap Zero) where they will simply continue to perform their functions until they die. Give examples of three cell types that are like this: neurons, heart cells, muscle cells 2) S Phase (Synthesis): The DNA is replicated creating two identical copies of each chromosome. As well, the centriole pair also duplicates to two create pairs. 1 centriole pair 2 centriole pairs 1 set of chromosomes Fig.7 S Phase Events 2 sets of chromosomes 3) G2 Phase (Gap 2): prepares growth The cell for mitosis by undergoing rapid of its cytoplasm. The cell increases the synthesis of the proteins needed to make the used in mitosis. The DNA is checked for replication errors that might have occurred during DNA replication in S Phase. This prevents mutations (changes in the DNA code) from being passed to daughter cells.

4 4 Mitosis 9. Mitosis: This process sorts and divides the duplicated chromosomes into two identical sets of DNA so that each daughter cell gets one set. 10. Mitosis is broken down into four main stages and they can be represented by the acronym P.M.A.T. which stands for 11. However, the events that occur between prophase and metaphase are important enough to create a fifth stage between these two called. prometaphase Fig.8 Stages of Mitosis Cytokinesis 12. Cytokinesis: The process that divides the cytoplasm in half to create two separate daughter cells. Animal Cells In animal cells, a cleavage furrow forms to constrict the cell membrane in the middle of the cell and divide it. Plant Cells In plant cells, the cell wall makes cytokinesis more challenging. Instead of making a cleavage furrow, a plant cell makes a cell plate in the middle of cell. The is made up of vesicles which contain the material needed to build the. cell wall The vesicles fuse at the midline of the cell to create a new cell wall which completely separates the two daughter cells. cleavage furrow cell plate Fig.9 Animal Cytokinesis Fig.10 Plant Cytokinesis

5 5 MITOSIS A CLOSER LOOK! G1 Interphase 13. In this example, we will examine a cell containing 3 chromosomes (red, blue and green) in the initial parent cell. G2 Interphase 14. After S Phase, each chromosome has undergone DNA replication. There are now. 3 duplicated chromosomes At this point, the DNA has not condensed yet so it is still long and. thin This thread-like form of DNA is called. chromatin 2 centrosomes 15. The two identical sides of each duplicated chromosomes are called sister. chromatids The two sister chromatids are connected together at a region of the chromosome called the. centromere / microtububles sister chromatids kinetochores centromeres 16. The centromere is where protein structures called kinetochores assemble on either side of the sister chromatids. The kinetochores are the sites of attachment for microtubules which pull the sister chromatids apart. 17. Microtubules are protein filaments that serve various different functions within a cell. When they are used in mitosis or meiosis, they can be specifically referred to as. 18. The centriole pair along with the proteins that surround it form the centrosome which is the organelle responsible for organizing the. microtubules Centrosomes are only found in animal cells. 19. Along with the DNA, the centrosome is replicated in S Phase to produce the two centrosomes you see in G2.

6 6 20. Fill in this chart to summarize the events in the various stages of mitosis. astral PROPHASE PROMETAPHASE equatorial plate kinetochore polar METAPHASE a) The centrosomes begin to migrate to. opposite poles b) Spindle fibers begin to form between the two centrosomes. c) The nuclear membrane begins to dissolve which frees the chromosomes to be sorted and divided in later stages of mitosis. d) The chromatin begins to condense and become, shorter thicker and. visible e) The nucleolus begins to disappear. a) The nuclear membrane is almost completely dissolved which allows the access to the duplicated chromosomes. b) The nucleolus has disappeared. c) Kinetochore reach through the dissolving nuclear membrane and attach to the kinetochores of each duplicated chromosome. These begin to position the duplicated chromosomes along the midline of the cell called the equatorial (or metaphase) plate. d) Polar from opposite poles reach the midline and push against one another to extend the distance between the two centrosomes. e) Astral help anchor the centrosomes at opposite poles of the cell. f) All of the different types of help form a network of fibers called the spindle apparatus (or ). mitotic spindle a) The centrosomes are fully migrated to opposite poles. b) The spindle apparatus is completely formed. c) The nuclear membrane is fully dissolved. d) The have lined up the duplicated chromosomes along the equatorial plate so that each sister chromatid of a duplicated chromosome faces opposite poles. e) Correct alignment at this stage helps to ensure that each new daughter cell will receive one sister chromatid from each duplicated chromosome when the sister chromatids are separated. f) At this stage, the chromosomes are, thick short and at their most, condensed hence the chromosomes are at their most easily observable state.

7 7 ANAPHASE a) The kinetochore shorten and pull the attached sister chromatids apart at the centromere towards opposite poles. b) The polar push against each other to elongate the cell and further separate the sister chromatids. c) Each chromatid becomes its own chromosome once separation has occurred. TELOPHASE cleavage furrow a) This phase is essentially the reverse of prophase. b) The spindle apparatus begins to. disassemble c) The chromosomes become long and thin by decondensing and reverting back to their chromatin structure. d) A nuclear membrane begins to reform around each set of chromosomes. e) The nucleolus reappears in each nucleus. f) A cleavage furrow (or cell plate in plant cells) begins to form which signals the beginning of cytokinesis which will separate the two new daughter cells. 21. Identify cells A-F as: interphase, prophase, prometaphase, metaphase, anaphase or telophase. prophase metaphase prometaphase telophase interphase anaphase

8 8 22. Identify cells A-E as interphase, prophase, metaphase, anaphase or telophase. (There s no prometaphase example in this image.) prophase anaphase telophase interphase metaphase