THE CELL CYCLE AND MITOSIS Lesson Objectives—Cell Cycle ► Describe the properties of cell division in prokaryotes. ► Describe cell division in eukaryotes. Explain the main differences between cell division in prokaryotic and eukaryotic cells. ► Describe the basic properties of chromosomes. ► Describe the key steps in the cell cycle. ► Identify and describe the main processes in mitosis. ► Describe how the cell cycle is controlled and define cancer. CELL REPRODUCTION ► Cell Division: process by which a cell divides to form two new cells (daughter cells) ► Three types of cell division, or cell reproduction ► Prokaryotes ► Binary (bacteria) fission🡪 divides forming two new identical cells ► Eukaryotes ► Mitosis ► Cell or organism growth ► Replacement or repair of damaged cells ► Meiosis ► formation of sex cells, or gametes PROKARYOTIC CELL DIVISION ►Binary fission ► 3 main steps: 1: DNA Replication—DNA is copied, resulting in 2 identical chromosomes 2: Chromosome Segregation—2 chromosomes separate, move towards ends (poles) of cell 3: Cytokinesis—cytoplasm divides, forming 2 cells ► Each new daughter cell is genetically identical to parent cell THE CELL CYCLE G1 phase M phase S phase G2 phase CELL CYCLE-INTERPHASE nterphase: period of growth and DNA replication between cell divisions ► Three phases: ► I ► G1 Phase ► cell ►S increases in size Phase ► Replication ► Now of chromosomes two strands called sister chromatids joined by a centromere ► G2 Phase ► organelles ► new ► All double cytoplasm forms other structures needed for mitosis form • DNA containing cell’s genetic code • Each chromosome has a matching pair -- Homologous Pair • During interphase, each chromosome copies itself EUKARYOTIC CELL DIVISION ► DNA found on chromosomes located in nucleus of cell ► Cell cycle continuous process ► Cells grow ► DNA replicated ► Organelles duplicated ► Divide to form daughter cells ► 2 Main steps: 1: Mitosis (4 steps—Prophase, Metaphase, Anaphase, Telophase) Nucleus divides 2: Cytokinesis—Cytoplasm divide, forming 2 cells Each new daughter cell is genetically identical to parent cell • Mitosis = nuclear division • Mitosis is followed by cytokinesis (cell division) • The steps of mitosis ensure that each new cell has the exact same number of chromosomes as the original MITOSIS ► Process that divides cell nucleus to produce two new nuclei each with a complete set of chromosomes ► Continuous process ► Four phases (PMAT) ► Prophase ► Metaphase ► Anaphase ► Telophase • • • • (1)Prophase (2)Metaphase (3)Anaphase (4)Telophase Interph ase 1 2 • PMAT 3 4 Cytokin esis 1. chromosomes visible (sister chromatids) 2. centrioles migrate to the poles (only in animals) 3. nuclear membrane disappears 4. spindle forms 1. chromosomes line up on the equator of the cell 2. spindles attach to centromeres Equator 1. sister chromatids separate 2. centromeres divide 3. sister chromatids move to opposite poles 1. chromosomes uncoil • now chromatin 2. nuclear membranes reform 3. spindle disappears - Occurs at end of Mitosis --division of the cytoplasm to form 2 new daughter cells --organelles are divided -Daughter cells are genetically identical Cells return to interphase Mitosis 1.Name the phases starting at the top. 2.Name the phase 3.Identify X 4.Identify Y 5. Name the phase 6. Name the phase Mitosis in a plant cell Chromatine Nucleus Nucleolus condensing Chromosome Metaphase. The 2 Prometaphase. 3 5 1 Prophase. 4 Anaphase. The spindle is complete, chromatids of each The chromatin We now see discrete and the chromosomes, chromosome have is condensing. chromosomes; each attached to microtubules separated, and the The nucleolus is consists of two at their kinetochores, daughter chromosomes beginning to identical sister are all at the metaphase are moving to the ends disappear. chromatids. Later plate. of cell as their Although not in prometaphase, the kinetochore yet visible nuclear envelop will microtubles shorten. in the micrograph, fragment. the mitotic spindle is staring to from. Figure 12.10 Telophase. Daughter nuclei are forming. Meanwhile, cytokinesis has started: The cell plate, which will divided the cytoplasm in two, is growing toward the perimeter of the parent cell. Control of the Cell Cycle ► Regulatory proteins called cyclins control the cell cycle at checkpoints: ► G1 Checkpoint—decides whether or not cell will divide ► S Checkpoint—determines if DNA has been properly replicated ► Mitotic Spindle Checkpoint—ensures chromosomes are aligned at mitotic plate Cell Cycle Checkpoints CANCER CELLS ► Result of uncontrolled cell division of cells that have lost ability to regulate cell cycle ► Reproduce more rapidly than normal cells ► Masses formed called ‘tumors’ ► Malignant tumors invade surrounding tissues and can metastasize ► Exporting cancer cells to other parts of the body where they may form secondary tumors Lymph vessel Tumor Blood vessel Glandular tissue 1 A tumor grows from a single cancer cell. Figure 12.19 Cancer cell 2 Cancer cells invade neighboring tissue. 3 Cancer cells spread through lymph and blood vessels to other parts of the body. Metastatic Tumor 4 A small percentage of cancer cells may survive and establish a new tumor in another part of the body. Lesson Summary—Cell Cycle ► ► ► ► ► ► ► ► ► ► The cell cycle is a repeating series of events, characterizing the life of a eukaryotic cell. Binary fission is a form of cell division in prokaryotic organisms that produces identical offspring. As a eukaryotic cell prepares to divide, the DNA and associated proteins coil into a structure, known as a chromosome. The DNA copies during the S phase of the cell cycle, resulting in a chromosome that consists of two identical chromatids, known as sister chromatids, attached at a region called the centromere. Any cell containing two sets of chromosomes is said to be diploid; the zygote forms from the fusion of two haploid gametes. The cell cycle has five phases: the first growth (G1) phase, the synthesis (S) phase, the second growth (G2) phase, mitosis, and cytokinesis. Mitosis is the division of the nucleus; four distinct phases of mitosis have been recognized: prophase, metaphase, anaphase, and telophase. Cytokinesis is the division of the cytoplasm. The cell cycle is controlled through feedback mechanisms. Cancer results from uncontrolled cell division, due to the loss of regulation of the cell cycle.
