Molecular Text 4.6

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  1. ·         Packaging of DNA into nucleosomes is crucial for evolution since __

    o   Each cell has a stored memory of its __. 
    complex multicellular organism are only possible if the cells in different lineages can specialize by changing the accessibility and responsiveness of many hundreds of genes to genetic readout.

    past developmental history in the regulatory circuits that control its many genes
  2. ·         The packaging of selected regions of eucryotic genomes into different forms of chromatin makes possible a type of __ with the crucial feature of __—in the fomr of __ that can persist for various lengths of the form of __that can persist for various lengths of time
    o   At one extreme are structures like __ that are stably inherited from one cell generation to the next
    • cell memory mechanism
    • storing memory of the stage of  gene on a gene-by-gene basis
    • local chromatin structure
    • local chromatin structures 
    • centric heterochromatin
  3. ·         Closely related mechanisms that are based on __ by the __ behind the __ are responsible for other type of condensed chromatin
    o   For example, the __ contains the __protein, whereas the __ that coats important developmental regulatory genes is maintained by the __
    • direct inheritance of parental forms of chromatin
    • daughter DNA helices
    • replication fork
    • permanently silenced, classical type of heterochromatin
    • HP1 
    • condensed chromatin
    • polycomb group of proteins
  4. §  The latter type of heterochromatin (condensed chromatin) does what, covering a total of about 2% of the human genome, and it is removed only when what?
    • silences a large number of genes that encode gene regulatory proteins early in embryonic development
    • each individual gene is needed by the developing organism
  5. ·         Although other types of inherited chromatin structures exist, it is unclear how many different types there are: the number could certainly exceed 10
    ·         Other forms of chromatin can have a shorter lifetime, much less than the division time of the cell; however, many have a __ that helps to mediate __
    • built-in persistence
    • biological function
  6. ·         Chromatin must be highly packaged into a series of __ and __; the chromatin packing is __, frequently changing in reponse to the needs of the cell
    • loops and coils
    • fluid
  7. ·         __ in growing amphibian oocyte are very unusual lampbrush chromosomes (the largest chromosomes known)
    o   Organization: a given loop always contains the __, and it remains extended in the same manner as the oocyte grows. These chromosomes produce large amounts of __for the oocyte, and most of the genes present in the DNA loops are being actively expressed. The majority of the DNA is not in __but remains __, where genes are generally not expressed
    • Meiotically paired chromosomes
    • same DNA sequence
    • RNA 
    • loops 
    • highly condensed in the chromore on the axis
  8. ·         __ of all eucaryotes are arranged in __which are very small and fragile. Yet, we can assess the frequency with which what, revealing likely candidates for the sites on chromatin that form the closely apposed bases of __.
    o   Human chromosomes are organized into __. 
    • Interphase chromosomes
    • loops
    • any two loci along an interphase chromosome are paired with each other
    • loop structures
    • loops of different lengths
  9. ·         Cells with more than the normal DNA complement are __when they contain increased numbers of standard chromosomes.
    o   Homologous chromosome copies create __, which can disperse to form conventional __ in some cases
    ·         Polyteny: __--> distinct alternating dark bands and light interbands are visible, formed from a thousand identical DNA sequences arranged side by side
    • polyploidy 
    • single large polytene chromosomes
    • polyploidy cells
    • when polytene chromosoems are studiedà
  10. o   95% of DNA in __is in bands; 5% is in __
    §  Thin bands: 3000 nucleotides/ Thick bands: 200,000 nucleotide pairs
    §  Bands are darker because of what; bands can be recognized by their different __ and __
    • polytene chromosomes 
    • interbands
    • the DNA is more condensed
    • thicknesses and spacings
  11. ·         By reading histone codes, specific sets of non-histone proteins do what?
    o   One of these non-histone proteins can spread for long distances along the DNA, doing what?.
    §  Thus, in some regions, all of the chromatin has a similar structure and is separated from neighboring domains by __ 
    assemble on the nucleosomes to affect biological function in different ways

    imparting a similar chromatin structure to contiguous regions of the genome

    barrier proteins
  12. ·         By staining an interphase chromosome with highly specific antibodies, one can show that __ are located on different __, suggesting a powerful general strategy.
    o   By employing combos of antibodies that bind tightly to each of the many different histone modifications that create the histone code, it may be possible to determine __
    • differently modified histones
    • polytene chromosome bands
    • which combo of modifications specify particular type of chromatin domains.
  13. ·         Each domain of heterochromatin is thought to be formed by the __
    o   For example,, __ contains more than __ such proteins, including __, whereas the so-called __ contains a similar number of proteins in a non-overlapping set (__) 
    • cooperative assembly of a set of non-histone proteins
    • classical pericentromeric heterochromatin
    • six
    • heterochromatin protein 1 (HP1)
    • Polycomb form of heterochromatin
    • PcG proteins
  14. ·         Other types of __must exist whose protein composition is not known; and, each type is differently regulated and has different roles in the cell
    ·         The chromatin structure in each domain ultimately depends on the __, and these are known to vary depending on the __ and its __
    • heterochromatin 
    • proteins that bind to specific DNA sequences
    • cell type
    • stage of development in a multicellular organism
  15. o   Thus, both the __ and __  can vary between tissues
    §  These differences make __, helping to explain the __ that accompanies __
    pattern of chromatin domains and their individual composition (nucleosome modifications plus non-histone proteins)

    • different genes accessible for genetic readout
    • cell diversification
    • embryonic development
  16. ·         When an insect progresses from one developmental stage to another, distinctive __ arise and __ recede in its __as new genes become __and old ones are __
    o   Most puffs arise from the __
    ·         The individual chromatin fibers that make up a puff can be visualized with an electron microscope, in which loops are seen
    • chromosome puffs
    • old puffs
    • polytene chromosomes 
    • expressed 
    • turned off
    • decompensation of a single chromosome band
  17. o   When not expressed, the __ assumes a thickened structure, possibly a folded 30-nm fiber, but when __ is occurring, the __becomes more extended
    §  In EMs, the chromatin located on either side of the __ appears considerably __, suggesting that a loop constitutes a __
    ·     Observations in human cells suggest that __ expand to occupy an __when a gene within them is expressed
    • loop of DNA
    • gene expression
    • loop 
    • decondensed loop
    • more compact
    • distinct functional domain of chromatin
    • highly folded loops of chromatin
    • increased volume
  18. ·         Each of the 46 interphase chromosomes in a human cell tends to occupy __.
    ·         __ are often closely associated with the __
    ·         Several experiments have led to the conclusion that the position of a gene in the interior of the nucleus changes when it becomes __
    • its own discrete territory within the nucleus.
    • Heterochromatic regions of a chromosome
    • nuclear lamina
    • highly expressed
  19. o   Thus, a region that becomes actively transcribed is often found to do what?
    §  __ requires the assembly of over 100 proteins, and it makes sense that this would occur most rapidly in region of the nucleus particularly__
    • extend out of its chromosome territory
    • Initiation of transcription
    •  rich in these protein
  20.     The nucleus is very __, with functionally different regions to which portions of chromosomes can move as they are subjected to different biochemical processes
    o   Some nuclear regions are marked with different __
    • heterogeneous
    • inositol phospholipids
Card Set:
Molecular Text 4.6
2015-01-25 19:52:31
Test One
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