DNA and Cell Division

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  • Created by: Sophie
  • Created on: 27-04-13 11:08


  • contains instructions to put an organism together and make it work
  • found in the nulcues in long molecules called chromosomes  
  • Gene- section of DNA contins instructions to make a specific protein by putting amino acids in order 
  • 20 amino acids used to make thousands of different protiens 
  • DNA determines what protiens the cell produces, determines type of cell
  • everyone has unique DNA (execpt identical twins) 
  • DNA fingerpriniting used for...
    • forensic science-crime scene 
    • paternity testing- see if a man is the farther of a particular child 
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Cell Division- Mitosis

  • used when plants and animals want to grow or to replace cells that have been  damaged
  • steps:
    • the cell grows
    • the cell duplicates all 46 chromosomes and these form x-shaped chromosomes (the left arm has the same DNA as the right of the chromosome) so that it has 92 chromosomes
    • the chromosomes line up in the middle of the cell
    • cell fibres pull the arms apart
    • membranes form around each set of chromosomes creating a nuclei for the two cells
    • cytoplasm divides
    • two cells have the same DNA so they are identical 

The six stages of mitosis (http://www.bbc.co.uk/schools/gcsebitesize/science/images/aqaaddsci_12_v2.gif)

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Asexual Reproduction

  • some organisms reproduce by mitosis
  • e.g. strawberry plants form runners by mitosis which form into new plants which are identical to the original strawberry plant
  • in asexual reproduction the offspring have exactly the same gene as the parent-there is not variation
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Cell Division-Meiosis (1)

  • gametes- sexcells- sperm and egg cells, 23 chromosomes each
  • step:
    • sperm and egg cells combine so that you have 46 chromosomes again
    • chromosomes are duplicated and from x-shaped chromosomes
    • the male and female chromosomes bond together and cross over forming new unique chromosomes
    • line up in centre of cell
    • pulled apart by fibres
    • pulled apart again forming four new unique gametes
    • sperm made constantly by man but only one of the four new gametes becomes an egg in a woman
    • after two gametes join at fertilisation the cells grow repeatedly by mitosis
  • meiosis produces variation because their is a mixture of chromosomes from each parent
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Cell Division- Meiosis (2)

chromosomes divide, similar chromosomes pair up, sections of DNA get swapped, pairs of chromosomes divide, chromosomes divide  (http://www.bbc.co.uk/schools/gcsebitesize/science/images/aqaaddsci_13.gif)

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