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ORGANISATION OF EUKARYOTIC GENOME (STRUCTURE OF (DNA (of chromosome…

- - - - single, double stranded molecule (chromatid)
      - multiple origins of replication
        
        increase rate of replication
        
        because of large size
      - multiple chromosomes bound by nuclear membrane in nucleus
    - - coding sequence (exons)
        
        codes for functional proteins
      - each gene has it's own promoter
        
        regulation of each gene occurs individually
      - exons interrupted by non-coding introns
        
        function: allow for alternative splicing
        
        allows one gene to code for multiple polypeptide
        
        structure: 'GT-------AG'
    - - circular, double stranded
  - - - two identical sister chromatids
      - chromatids joined at CENTROMERES
        
        constricted region of chromosome (220 nucleotides)
        
        composed of highly repeated sequence
        
        function
        
        sister chromatid adhesion
        
        kinetochore formation
        
        kinetochore: complex of proteins forms at each centromere
        
        attachment point for spindle fibres (separate sister chromatid during anaphase)
        
        importance
        
        aberrant function --> improper chromosomal alignment and segregation
        
        aneuploidy (chromosomal aberration) (ref. protein synthesis mutation)
      - TELOMERES at the ends of chromosomes (end of DNA molecule)
        
        Specialised DNA sequences
        
        found at the end of linear DNA
        
        already exists - NOT LIKE 5' CAPPING WHERE IT'S ADDED BUT IT IS ALREADY THERE
        
        repeat of DNA sequence (5' TTAGGG3')
        
        function
        
        postpone erosion of genes via successive rounds of replication
        
        caused by end replication problem (ref. protein synthesis)
        
        telomeres shortened instead of critical genes
        
        telomeres extended by telomerase
        
        2 more items...
        
        act as buffers
        
        prevent loss of crucial genes as chromosome shortens
        
        prevent degradation of ends of linear DNA molecules by deoxyribonuclease
        
        maintain integrity of chromosomal end
        
        prevent fusion of chromosomal end between chromosomes
        
        importance
        
        fusion of exposed ends disrupts regulation of genes on adjoined chromosomes :
        
        prevents DNA repair machinery from recognising and sticking together ends of chromosomes when there are chromosome breaks
        
        1 more item...
        
        limit lifespan of cells
        
        when critical length of telomere reached
        
        cells undergo apoptosis
        
        because in somatic cells telomerase is inactive
        
        importance
        
        limits extent of accumulated mutations
        
        prevents development of cancerous cells
  - - - nucleotide sequence upstream of a gene
      - general transcription factors and RNA polymerase attach to initiate transcription of mRNA
    - - nucleotide sequence located far away (>1000bp) from transcription start site (upstream or downstream)
      - activator proteins attach to activate transcription
    - - nucleotide sequence located far away (>1000bp) upstream of transcription start site
      - repressor proteins attach to suppress transcription
- - - - linker DNA joins adjacent nucleosomes (brings nucleosomes together)
        
        DNA not associated with histones (in between nucleosome) is linker DNA
        
        coiling of nucleosomes into a helical structure
        
        chromatin packed together into one long rope like structure (FYI)
      - Formation of loop domains
        
        solenoid structure forms loops anchored by non-histone scaffolding proteins
        
        formation of chromosome
        
        scaffolding proteins further coiled and folded
    - - H1 histone fastens DNA to nucleosome core
        
        nucleosome core: histone cramer (8 histones that DNA is wrapped around)
  - - - lightly condensed
        
        nucleosome structure (level of coiling)
        
        parts lack nucleosome (just DNA) so other proteins and transcription factors can bind to DNA
        
        allows access of RNA polymerase to transcribe the genes
        
        genes are actively expressed
      - appear in light microscope: lightly stained region
    - - highly condensed form
        
        solenoid and more condensed structures
        
        genes not expressed
        
        structure of DNA
        
        structure: transcriptionally inactive genes
        
        doesn't allow access to RNA polymerase and transcription factors (because compact)
        
        structure: made up of repetitive sequences and don't contain genes
        
        concentrated in centromeres and telomeres
  - - - histone: changes charge and affects association between DNA (ref. nucleosome formation)