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1.6 Cell Division/Mitosis

1.6 Cell Division/Mitosis. Question?. Why would a cell want or need to divide? Growth/development of tissues/organs Repair of damaged tissue/organ Reproduction of cells/organisms. Cell Cycle. The cell’s life cycle (usually just called the cell cycle) consists of two main parts:

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1.6 Cell Division/Mitosis

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  1. 1.6 Cell Division/Mitosis

  2. Question? • Why would a cell want or need to divide? • Growth/development of tissues/organs • Repair of damaged tissue/organ • Reproduction of cells/organisms

  3. Cell Cycle • The cell’s life cycle (usually just called the cell cycle) consists of two main parts: • Interphase – active period in the life of a cell when many metabolic reactions occur, including • protein synthesis • DNA replication • an increase in the number of mitochondria and/or chloroplasts • Mitosis– cell divides

  4. Cell Cycle • Interphase can be divided into three phases: • G1 – cell grows and metabolizes • S – DNA is replicated • G2 – cell prepares for division

  5. Mitosis • Mitosis can be divided into four stages: • Prophase • Metaphase • Anaphase • Telophase

  6. Mitosis • Prophase • Nuclear envelope disappears • With the aid of special proteins called histones, DNA supercoils into distinct chromosomes that are visible under the microscope • Each pair of identical segments of DNA, called sister chromatids, bind together at the centromere to form one chromosome

  7. Prophase • Centrioles moved to opposite ends of the cell • Long, tubular proteins called “spindle fibers” grow from the centrioles and attach to the centromeres of the chromosomes

  8. Metaphase • Spindle fibers pull chromosomes to the equator (center line) of the cell

  9. Anaphase • Spindle fibers shorten • Sister chromatids are pulled apart and are now called chromosomes • Chromosomes are pulled to opposite ends of the cell

  10. Telophase • Reverse of prophase: • Spindle fibers dissapear • DNA uncoils and becomes chromatin • Nuclear envelope reforms

  11. Cytokinesis • Splitting of the cytoplasm • Occurs when microtubule proteins pinch inward at the equator (cleavage furrow) • Results in two separate but identical cells

  12. Plant Cell Division • In plants a cell plate forms instead of a cleavage furrow

  13. Overview • Mitosis produces two genetically identical nuclei • During the S phase of interphase DNA is replicated to produce two identical copies • During prophase the identical copies of each chromosome (homologous chromsomes) bind together • Homologous chromosomes are pulled apart during anaphase and become part of two separate nuclei during telophase

  14. Mitosis serves many purposes: • Tissue/organ growth • Embryonic devleopment, when the zygote divides to produce many smaller cells • Tissue damage and repair • Asexual reproduction (unicellular organisms)

  15. Control of this process • Cyclins • Series of proteins that control cells during cell cycle.

  16. Not always controlled • Mutagens – • Physical or chemical agent that changes the DNA in an organism. • This increases the frequency of mutations in that organism above the natural background level. • Often these mutagens can cause cancer/tumors

  17. Oncogenes • Sometimes the gene controlling cell division (called an oncogene) will become mutated • The result is that cell division continues repeatedly • This is how tumors are formed • Tumors can form in any tissue of the body Stomach Tumor

  18. Metastasis • Greek for “Next Placement” • Cells that are going through uncontrolled proliferation can sometimes slough off of a tumor and spread through the body to another area that previously was unaffected. • These cells will continue their rapid mitotic division and cause the disease to spread.

  19. Tumors • Tumors are a mass of cells that are going through mitosis uncontrollably due to a mutation in the DNA • Two major types: • Malignant: “Badly Born” can spread to invade other cells throughout the body. • Benign: lacks the ability to invade neighboring cells

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