Molecular and Cellular Biology (2)

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  1. True or False: Every chromosome has both heterochromatin and euchromatin while in interphase.
  2. Describe Heterochromatin.
    Highly condensed throughout cell cycle

    Characteristic feature of centromeres, telomeres, seen at some other (often ill-defined) chromosomal locations

    Typically composed of highly repetitive DNA sequences (tandem repeats)

    Generally contains very few genes – exhibits little transcription

    Genes translocated into heterochromatic sequence (through chromosome breakage and rejoining) are typically transcriptionally inactivated

    Every female (2X) somatic cell contains one inactive X chromosome (the “Barr body”) that is heterochromatic and highly condensed
  3. Describe Euchromatin.
    Becomes highly condensed only at metaphase

    • Intermediate level of condensation
    • during interphase

    Represents the major portion of chromatin – contains most of the genes

    BUT, genes within it can be transcriptionally active or inactive
  4. What is the physical form of euchromatin during interphase?
    30nm Fiber
  5. In chromatin, what is the raito of dna to proteins by weight?
    1 dna : 2 proteins
  6. In chromatin, what is the ratio of non-histone proteins to histone proteins by weight?
    1 : 1
  7. In chromatin, what is the ratio of DNA to RNA by weight?
    1 DNA : 0.06 RNA
  8. Is the H1 histone as conserved as much as the other histones?
    No. It has the ability to be changed without losing functionality.
  9. What protein subunits make up the histone octomer?



  10. Describe the structural organization of histone proteins.
    3 Alpha Helix structures

    Highly conserved N terminus tail ( 20-30 AA with highly positive charge.)
  11. Describe the formation of the histone octomer.
    Two H3 & H4 dimers come together. Then H2A & H2B dimers attach to the front and the back.
  12. The process of histone octomer formation is catalyzed by _____, which are called _____.

    Chromatin Assembly Factors (CAFs)
  13. How many base pairs are part of a nucleosome?
  14. DNA is wound around the core octamer _____ times in a _____ superhelical turn.

    Left Handed
  15. How are nucleosomes pulled together in the 30nm fiber?
    The basic residues located on the tails of the histone subunnits attach to the acidic residues of other octomers.
  16. Histone H1 has _____ separate DNA binding sites that allow it to tether the _____ to the _____.


    Core nucleosome
  17. the long _____ allows adjacent H1 Molecules to interact with one another, which allows nucleosomes to pack tightly into the 30nm fiber.
  18. The average spacing of the nucleosome is _____ bp and the average linker length is _____bp.

Card Set
Molecular and Cellular Biology (2)
Test 1
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