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Title: DNA packaging
Description: for 2nd year students studying Genes and Inheritance modules
Description: for 2nd year students studying Genes and Inheritance modules
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DNA packaging
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Needs to be packaged for protection and to be able to fit inside the nucleus
Chromatin – combination of DNA and proteins found in the eukaryotic cell nuclei
Functions of chromatin:
->Package DNA into a smaller volume to fit in nucleus
->Strengthen DNA to allow mitosis
->Prevent DNA damage
->Control gene expression and DNA replication
• Primary protein components of chromatin are HISTONES
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Nucleosomes formed from DNA and histone proteins
DNA is wrapped around histone octamers to form nucleosomes
Nucleosomes then compacted into chromatin fibre
Heterochromatin and Euchromatin
• Euchromatin – less condensed
->regions involved in transcription
->contain unique sequences ie genes
• Heterochromatin – condensed chromatin
->often contains repetitive DNA
->usually NOT transcribed
->RNA polymerase CANNOT access gene to transcribe it into mRNA = NO GENE EXPRESSION
X chromosome inactivation
• DNA packaging controlling GE
• X chromosome contains 800 protein coding genes
• Females have 2 X chromosomes
• Only need 1 X chromosome to be active in cell, other has to be inactivate
• In calico cats fur pigmentation is linked to X chromosome, depending on which copy of X
chromosome is activated in each cell will display both orange and black fur
Title: DNA packaging
Description: for 2nd year students studying Genes and Inheritance modules
Description: for 2nd year students studying Genes and Inheritance modules