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Understanding Cell Division: Stages, Tumours, and Control Mechanisms

Learn about the stages of the cell cycle, including interphase, mitosis, and cytokinesis. Explore the checkpoints during cell division and the formation of tumours due to uncontrolled cell division. Discover the factors that affect cell division and the role of growth factors in the cell cycle control system.

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Understanding Cell Division: Stages, Tumours, and Control Mechanisms

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  1. TOPIC 2.5 CELL DIVISION

  2. 2.5.1Outline the Stages of the Cell Cycle • The stages include interphase (G1, S and G2), mitosis and cytokinesis • Important terms: • Mitosis= process of nuclear division • Cytokinesis= after mitosis this is the actual physical division of the cell (not part of mitosis) • Stage G1= period of cell growth and increase in number of organelles • Stage S= synthesis of DNA occurs (replication) • Stage G2= growth and preparation for mitosis

  3. http://www.youtube.com/watch?v=Q6ucKWIIFmghttp://www.youtube.com/watch?v=AGEu88ujn5whttp://www.youtube.com/watch?v=Q6ucKWIIFmghttp://www.youtube.com/watch?v=AGEu88ujn5w

  4. Checkpoints in the cell cycle: • There are 3 checkpoints during the cell cycle where the cycle will stop if there is a problem: • during G1 • end of G2 • end of mitosis • The cell goes into G0 and will not reproduce • http://www.youtube.com/watch?v=AGEu88ujn5w

  5. 2.5.2 Tumours are the result of uncontrolled cell division • Tumours can occur in any organ or tissue • Tumours are formed by immortal cancer cells • Cell division is controlled- only cells needed for growth and/or repair are produced through mitosis • Tumour repressor genes produce proteins which inhibit cell division • Proto-oncogenes are genes that produce proteins which stimulate growth and cell division • If mutations occur in these 2 genes cell division can become uncontrolled, resulting in a tumour

  6. Anchorage, cell density, and chemical growth factors affect cell division • An organism must be able to control the timing of cell division • Anchorage dependence • Most animal cells must be in contact with a solid surface to divide • Density-dependent inhibition • Cells form a single layer • Cells stop dividing when they touch one another • Inadequate supply of growth factor causes division to stop

  7. Cells anchor to dish surface and divide. When cells have formed a complete single layer, they stop dividing(density-dependent Inhibition). If some cells are scraped away, the remaining cells divide to fill the dish with a single layer and then stop (density-dependent inhibition). After forming a single layer, cells have stopped dividing. Providing an additional supply of growth factors Stimulates further cell division.

  8. Growth factors signal the cell cycle control system • The cell cycle control system regulates the events of the cell cycle • If a growth factor is not released at three major checkpoints, the cell cycle will stop • G1 of interphase • G2 of interphase • M phase G1 checkpoint G0 Control system G1 S G2 M M checkpoint G2 checkpoint

  9. How a growth factor might affect the cell cycle control system • Cell has receptor protein in plasma membrane • Binding of growth factor to receptor triggers a signal transduction pathway • Molecules induce changes in other molecules • Signal finally overrides brakes on the cell cycle control system

  10. Growth factor Plasma membrane LE 8-9b Relay proteins Receptor protein G1 checkpoint Signal transduction pathway Control system S G1 G2 M

  11. Growing out of control, cancer cells produce malignant tumors • Cancer cells do not respond normally to the cell cycle control system • Divide excessively • Can invade other tissues • May kill the organism

  12. Carcinogens • Cancer causing agents • Certain types of radiation • ex. Ultraviolet light increases chance of skin cancer • Certain chemicals • viruses • Increase the chance of mutations or increase the effects of mutations which are already present

  13. Some tumours are harmless = benign • ex. Warts • Some tumours are malignant and spread (metastasize) to other parts of the body • Treatments: • Surgical removal- before they grow and spread • Radiation therapy- nuclear radiation beam targeting a precise point to “burn” all cells in the area • Chemotherapy- chemicals that destroy all rapidly dividing cells by medication (includes hair, lining of gut, sperm production) many side-effects

  14. If an abnormal cell avoids destruction by the immune system, it may form a tumor • Benign: abnormal cells remain at original site • Malignant: abnormal cells can spread to other tissues and parts of the body • Metastasis: spread of cancer cells through the circulatory system

  15. 2.5.3 Interphase of the cell cycle involves: protein synthesis, DNA replication, and an increase in organelles • Cell Cycle includes: interphase, mitosis and cytokinesis • Mitosis= nuclear division • Cytokinesis= division of the cell • Interphase includes: (about 90% of the cell cycle) • G1 or Gap 1- cell grows, replicates organelles, and perform normal cell activities • S or Synthesis- DNA replicates • G2 or Gap 2- cell continues to grow

  16. Interphase • Used to be called the “resting phase”, but scientists realized that this is a very active phase of a cell’s life cycle • Many biochemical reactions • Transcription and translation • DNA replication • Replication of organelles • Growth • During G2 the number of chloroplasts and mitochondria increases • Cell cycle varies between different cells • Bacteria= 20 minutes skin cell= 14 days RBC= 4 months liver cell= 300-500 days • The above times vary depending on conditions

  17. 2.5.4 Describe the 4 phases of Mitosis • Mitosis = nuclear division • 4 phases include: prophase, metaphase, anaphase and telophase PMAT • The purpose of mitosis= increase the # of cells without changing the genetic material • The 2 daughter cells which result are identical to each other and to the origin parent cell • When the cell is not dividing it is in interphase

  18. InterphaseHappens BEFORE Mitosis • G1 , S and G2 • The cell grows, makes more organelles and replicates its DNA (replication happens in the S phase of interphase) • During interphase chromosomes are NOT visible, but appear as long stringy strands • DNA is called chromatin when it is loose • The DNA is wrapped around proteins (histones) and looks like “beads on a string” • Prokaryotic cells DNA is “naked” (not associated with proteins

  19. Prophase • Chromosomes become visible (supercoiled) • Centrioles move to opposite poles • Spindles form • Nucleolus disappears • Nuclear membranes disappears • Each chromosome has an identical copy attached to it (sister chromatid) at the centromere

  20. Metaphase • Chromosomes move to the equator • Spindle microtubules attach to the centromeres

  21. Anaphase • Centromeres separate • Chromatids separate and move to opposite poles • Once the sister chromatids separate they are called chromosomes

  22. Telophase • Chromosomes have arrived at the poles • Spindle disappears • Centrioles replicate (in animal cells) • Nuclear membrane reappears • Nucleolus becomes visible • Chromosomes uncoil and become chromatin

  23. Cytokinesis • The division of the cell into two identical cells • This happens after mitosis • Different in plant and animal cells • Animal cells form a cleavage furrow and the cell pinches into two • Plant cells form a cell plate which becomes a cell wall

  24. 2.5.5 Explain how mitosis produces two genetically identical nuclei • Result of mitosis = two nuclei • During S phase of interphase the chromosomes replicate (form an exact copy) • These copies are called sister chromatids • Sister chromatids separate during anaphase (so they are now called chromosomes) • They move to opposite poles and during telophase are surrounded by a nuclear membrane • SO the result is 2 nuclei identical to each other and the original

  25. Mitosis Video Clip • http://video.search.yahoo.com/search/video;_ylt=A0S00My4yF5StRYAvHf6w8QF?p=mitosis&ei=utf-8&fr=yhs-w3i-syctransfer&fr2=sfp-vid • http://www.youtube.com/watch?v=65SODTL_QsA

  26. 2.5.6What processes of organisms involve mitosis??? • Embryonic Development- we all started as one cell (a zygote or fertilised egg) and became multicellular by mitosis. As the number of cells increase, differentiation takes place by expressing some genes and not others • Replacement and repair- we are constantly replacing dead or damaged cells • Growth- as we grow and develop we need to add more cells to our body • Asexual Reproduction-production of identical cells by mitosis ex. Vegetative reproduction in some plants

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