Chapter 4

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Chapter 4
2010-10-19 13:26:46
Cellular Molecular biology

DNA, chromosomes, and genomes
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  1. The haploid human genome consists of ~______ nucleotide pairs.
    3.2 billion
  2. Define: chromatin
    • unpackaged DNA material (unwound chromosome)
    • Chromatin condenses in Mitosis
  3. Define gene;
    a gene is a sequence of DNA that codes for one polypeptide or one set of closely related polypeptides (via alternative splicing), or a structural RNA, or a regulatory RNA.
  4. Human cells have ~ _____ genes
    ~25,000 genes
  5. only ~___% of DNA codes for proteins.
  6. all noncoding DNA is termed _____ ___
    "junk DNA"
  7. a Simple sequence repeat is a _____
    short nucleotide sequences (>14 NP's) that are repeated again and again for long stretches.
  8. Mitosis is ~____hr in many mammalian cells
  9. 2 groups of protein that package DNA;
    • 1) Histones
    • 2) nonhistones
  10. Histones package DNA into ________
  11. A nucleosome consists of;
    • 1) a nucleosome core particle
    • 2) Linker DNA - few np's to 80 np's long to the neighbouring nucleosome
  12. The are _ core histones.
    8. A pair of H2A, H2B, H3, and H4 histones.
  13. Each core histone has a structural motif (region) called a ____ ____
    Histone fold.
  14. Describe the joining process of the core histone octamer.
    • H3 and H4 form a dimer and then join a similar dimer, forming a tetramer.
    • H2A and H2B form a dimer as well, join a similar dimer, and form a tetramer as well.

    • The 2 differnt tetramers join to form the octamer.
  15. What will you find on each end of a histone fold?
    • One N-terminal tail end - amino end
    • other end: carbonyl end
  16. What is nucleosome sliding and how is it accomplished?
    • Nucleosome sliding is the act of pushing the DNA wrapped around the histone core. It is catalyzed through ATP-dependant chromatin remodeling complexes. (uses the energy of ATP hydrolysis).
  17. True/False: H1 is a core histone.
    • False. H1 is not apart of the nucleosome core particle.
    • one histone H! binds to each nucleosome
    • H1 is also a linker histone
  18. 2 major types of chromatin include;
    Heterochromatin and euchromatin.
  19. Describe heterochromatin.
    • Condensed
    • transcriptionally inactive
    • contains few genes
    • genes present are to dense to read
  20. Describe euchromatin;
    transcriptionally active.
  21. _______ causes modifications to core histone tails.
    • Histone-modifying enzymes.
    • Methylation, phosphorylation, acetylation and ubiquitylation
  22. Where can heterochromatin be found?
    telomeres, and in/around the centeromere.
  23. ______ describes heterochromatin around the centromere.
    pericentric heterochromatin.
  24. ______ _______ describes heterochromatin within the centromere.
    centric heterochromatin.
  25. ______ molecules link sister chromatids.
    Cohesion molecules.
  26. Centromere Nucleosomes: special proteins called _____ _____ bind to the centromere DNA and form _____ _______.
    centromere-specific proteins; centromere-specific nucleosomes.
  27. Chromosomes are folded into large loops of chromatin are known as _______ chromosomes; found in growing amphibian oocytes.
    Lampbrush chromosomes. (largest chromosome known)
  28. A chromomere is ____
    the region on the lampbrush chromosome (end of loop) on the axis of DNA; highly condensed regoin of DNA where genes are generally not expressed.
  29. protein responsible for forming the mitotic "X" chromosome.
  30. Condensins bind to chromatin to ___ into the _____ chromosome.
    coil; mitotic
  31. This enzyme can be used to digest linker DNA
    Nuclease. Cannot digest DNA wrapped around core histones
  32. linker DNA is about _____ np's long
    200. Wrapped around the histone core ~ 1.7 times.
  33. What is the function of the N-terminal tail in the histone core?
    plas a role to package the nucleosome into thicker fibers
  34. True/false: There is a single ATP-dependant chromatin remodeling complex?
    False. There are many different chromatin remodeling complexes
  35. Histone-modifying enzymes modify which region of the histone?
    N-terminal tail
  36. Histones may be methylated and acetylated only.
    False, histone N-terminal tails made undergoe methylation, acetylation, phosphorylation as well as ubiquitylation (single ubiquiton)
  37. A histone code is thought to exist because ...
    modifications may cause gene silencing, heterochromatin formation, gene expression, silencing of Hox genes
  38. Nucleosomes pack into the ______ model.
    zig-zag model into 30 nm chromatin