THE ORGANIZATION AND CONTROL OF EUKARYOTIC GENOMES

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CHAPTER 19
THE ORGANIZATION AND CONTROL OF EUKARYOTIC GENOMES
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Euchromatin _________________________
________________________ Heterochromatin
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Embryonic cells are totipotent and can express
all their DNA. Adult stem cells are
pluripotent As cells specialize they go through
cell differentiation and convert more and more of
their DNA from euchromatin to heterochromatin. He
terochromatin is coiled to the looped domain
level or more and can not be transcribed.
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euchromatin 30nm chromatin fiber
heterochromatin
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DNA that is methylated will condense to the
heterochromatin level plays a part in genomic
imprinting and deactivation of genes Histone
acetylation-the attachment of acetyl groups to
certain amino acids causes the histones to grip
the DNA less tightly and thus it can be
transcribed more readily. Histone deacetylation
causes the DNA to coil more tightly and become
heterochromatin. A typical specialized human
cell only uses 3-5 of its DNA at any given
time and 85 will be coiled in the form of
heterochromatin.
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Tandemly Repetitive DNA-Satellite DNA-long
sections of short (less than 10 base pairs)
tandem 10-15 of DNA Centromeres and telomeres
related to fragile X syndrome and Huntingtons
triplet of CAG causes many glutamines to be coded
into the protein Interspersed Repetitive
DNA-transposons-25-40 of DNA and increasing (if
most of these are transposons, then they make up
most of our genome) 100-10,000 base pairs long
also includes Alu elements-they are actually
retrotransposons and there are over 1 million
copies of this 300 nucleotide sequence in the
human genome and composes over 10 of the
genome Gene amplification-making extra copies of
genes that are in high demand rRNA in amphibians
and mammalian oocytes so they can make thousands
of ribosomes rapidly
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The effect of a transposon on flower color
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Barbara McClintock identified moveable
controlling elements in corn in the 1950s
finally awarded the Nobel prize in 1983.
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Three of the hundreds of copies of rRNA
transcription units in a salamander
genome. Multigene families- identical- rRNA,
tRNA, histones nonidentical-globin genes
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The evolution of the human alpha-globin and beta
globin gene families
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Retrotransposition movement
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DNA rearrangement in the maturation of an
immunoglobulin gene
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Opportunities for the control of gene expression
in eukaryotic cells 1. DNA packing 2.
transcription 3. processing 4. transport to
cytoplasm 5. degradation of mRNA 6. modification
and transport of proteins 7. RNA
interference 8. degradation of proteins
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A eukaryotic gene and its transcript
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A model for enhancer action
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The three major types of DNA-binding domains
(part of promoters) in transcription DNA-binding
domain-a part of the DNA to which a transcription
factor can bind the same transcription factor
may attach to all the promoters of all the genes
for a metabolic pathway
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Alternative RNA splicing
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Degradation of a protein by a proteosome
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Proteosomes
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Genetic changes that can turn proto-oncogenes
into oncogenes
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p53 gene - its protein product is called the
guardian angel of the genome damage to a
cells DNA leads to transcription of the p53
protein which functions as a transcription factor
that -halts cell cycle by binding to
cyclin-dependent-kinases -turns on genes that
repair DNA -turns on genes that cause apoptosis
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Signaling pathways that regulate cell growth
Cyclin or Cdk
protein from p21 gene
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A multi-step model for the development of
colorectal cancer
p53 gene codes a transcription factor protein
that Activates p21gene whose product halts the
cell cycle by binding to cyclin-dependent kinases
allowing time for DNA repair Activates genes
whose proteins repair DNA Activates suicide genes
causing apoptosis