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Chromosomes (what are chromosomes? (G banding (lighter bands corresponds…

- - - - a portion of the chromosome is deleted or missing
    - - a portion of the chromosome is duplicated resulting in extra genetic material
    - - a portion of one chromosome is transferred to another chromsome
    - - a portion of the chromosome has been removed, reversed and reattached --> genetic material is inverted
    - - a portion of a chromosome hzs broken off formed a ring and been reattached
        
        can happen with or without loss of genetic material
  - - - 2 x chromosomes one Y chromosome
        
        genitalia
        
        wide hips and breasts
        
        infertility
    - - mental retardation
      - learning difficulties
      - characteristic facial exression
      - 3 copies of chromosome 21
    - - one sex syndrome, X
      - short size
      - infertility
    - - part of chromosome 5 is deleted
- - - - histone proteins
        
        responsible for the first and most basic form of chromosome packing to form the nucleosome
      - non-histone like proteins
      - when these proteins bind to DNA, they form chromatin
      - composition of proteins
        
        made up of dimers of the H2A, H2B, H3 and H4 proteins
        
        they come together to form the cylindrical shaped protein complex around which the DNA is wound
        
        approximately 147 nucleotides are wound around this protein complex 1.7 times
    - - linker DNA ensures that each core particle is spaced evenly apart
    - - linker DNA between each core particle can be digested to release the "beads"
    - - involved considerable compression of the minor groove of the DNA helix
      - some nucleotides are more easily compressed while other show a greater affinity for interacting with the histones than others
        
        GC residues to be located on the outer side
        
        AT, TT or AA dinucleotides are located on the inner side
        
        preferences have to be weak enough to allow the nucleosomes to form at any none of a number of locations along wiht the DNA sequence
  - - - tail domains that protrude out of the core particle and interact with the tails of nearby core particle tethering them together.
      - histone H1 changes the direction of the DNA as it exits the nucleosome
        
        allowing the chromatin to become more densely packed.
- - - - in order to be activated: H3 proteins have to be methylated
  - - - achieved through the activity of an ATP dependent chromatin remodelling complex.
    - - methylation / acetylation of histone protein tails
      - examples
        
        methylation at the lysine residue at position 9 then the gene bound up in the nucleosomes will be silenced
        
        acetylated in the same position together with methylation at position 4 the gene will be activated
        
        If the serine residue at position 10 is phosphorylated and the lysine at position 14 acetylated then this will also lead to gene activation