Cell division

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Cell division

  1. 1. CELL DIVISION CELL DIVISION
  2. 2. Cell division – what is it for? <ul><li>Remember the cell theory: </li></ul><ul><ul><li>Cells can only come from pre-existing cells </li></ul></ul><ul><li>Cell division is when your cells divide. The original cell ( parent cell ) divides into two daughter cells . </li></ul><ul><li>Needed for growth, repair and reproduction. </li></ul><ul><li>When you grow, you need more cells so your existing cells divide to make more cells. </li></ul><ul><li>New cells need to be made to replace dead or injured cells. </li></ul><ul><li>Cell division is also needed to make babies. Cells need to divide to make egg cells (ova) and sperm cells. </li></ul>
  3. 3. DNA replication <ul><li>Remember: All cells have a nucleus and each nucleus have DNA. DNA controls everything. </li></ul><ul><li>This means that if one cell is to divide into two cells, DNA needs to be copied. </li></ul><ul><li>One DNA can be copied to make two DNA in DNA replication . </li></ul><ul><li>The DNA unzips. Each DNA strand copies itself to become two DNA. </li></ul>
  4. 4. DNA needs to copy exactly <ul><li>DNA needs to copy themselves exactly so everything looks the same and works the same. Eg. Skin cells dividing into skin cells. </li></ul><ul><li>Sometimes when DNA are copying themselves, they will make mistakes. These mistakes are called mutations . </li></ul><ul><li>Most of the time, the body will fix the mutations. </li></ul><ul><li>When mutations aren’t fixed, diseases such as cancer can occur. </li></ul><ul><li>But sometimes mutations can be good for the organism. </li></ul>
  5. 6. What happens next? <ul><li>So far only DNA has copied. </li></ul><ul><li>Remember: DNA are located on chromosomes. </li></ul><ul><li>After DNA has copied itself, chromosomes become double stranded. </li></ul><ul><li>Now the cell can start dividing. </li></ul><ul><li>Mitosis : when cells divide </li></ul>
  6. 7. Mitosis
  7. 8. Meiosis <ul><li>Mitosis – when body cells divide </li></ul><ul><li>Meiosis – when sex cells divide </li></ul>
  8. 9. Differences between mitosis and meiosis Mitosis Meiosis Number of parent cells 1 1 Number of daughter cells 2 4 DNA and genes in daughter cells Exactly the same as parent cells Different from parent cells Number of chromosomes in daughter cells 2n = 46 n = 23 Purpose Growth and repair Reproduction
  9. 10. Why 23 chromosomes? <ul><li>Fertilisation – 23 chromosomes from sperm + 23 chromosomes from egg = 46 chromosomes </li></ul>
  10. 11. Cell Division – mitosis and meiosis <ul><li>Cell division is when one parent cell divides into two daughter cells </li></ul><ul><li>Needed for growth, repair and reproduction </li></ul><ul><li>Before a cell can divide, DNA needs to replicate </li></ul><ul><li>DNA needs to copy itself exactly to make sure all cells look and function the same way as the parent cell </li></ul><ul><li>A mutation is when DNA doesn’t copy itself exactly. This can lead to diseases such as cancer. </li></ul><ul><li>However, sometimes a mutation can give an organism an advantage. </li></ul><ul><li>After DNA has replicated, the cell will have double-stranded chromosomes </li></ul><ul><li>Then the cell can undergo mitosis to divide into two cells – daughter cells are genetically identical and have 46 chromosomes </li></ul><ul><li>Meiosis is the division of sex cells – daughter cells genetically different and have 23 chromosomes </li></ul>

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