THE ORGANIZATION AND CONTROL OF EUKARYOTIC GENOMES

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CHAPTER 19
THE ORGANIZATION AND CONTROL OF EUKARYOTIC GENOMES
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1. The average human chromosome has 150 million
base pairs(1.5 x 108) 2. Completely stretched
out it would be 4 cm. long 3. All 46 would
stretch 184 cm. or almost 2 meters 4. All the DNA
in all the cells in your body would reach to
the sun and back!!! 5. We have 2.2 billion base
pairs in every cell. 6. But we have only
20,000-25,000 genes, a surprisingly low
number for our species. Consortium
researchers have confirmed the existence of
19,599 protein-coding genes in the human
genome and identified another 2,188 DNA
segments that are predicted to be
protein-coding genes. 7. Only 1-3 of our DNA
codes protein. Structure and expression of the
gene encoding phosphofructokinase (PFK) in
Drosophila melanogaster.
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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 2-4 of its DNA at any given
time and 95 will be coiled in the form of
heterochromatin.
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44 repetitive DNA transposons and related
sequences 24 Introns and regulatory sequences
promoters 15 Unique noncoding DNA 15 repetitive
DNA unrelated to transposons 1.5 Exons for
proteins, rRNA and tRNA
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Interspersed Repetitive DNA-transposons-44 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 --42 of the entire human genome consists
of retrotransposons. Kimball biology 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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Tandemly Repetitive DNA-Satellite DNA-long
sections of short tandem 15 of genome
Centromeres and telomeres related to fragile X
syndrome Satellites are very highly repetitive
with repeat lengths of one to several thousand
base pairs. These sequences typically are
organized as large (up to 100 million bp !)
clusters in the heterochromatic regions of
chromosomes, near centromeres and telomeres
these are also found abundantly on the Y
chromosome.
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Minisatellites are moderately repetitive,
tandemly repeated arrays of moderately-sized (9
to 100 bp, but usually about 15 bp) repeats,
generally involving mean array lengths of 0.5 to
30 kb. They are found in euchromatic regions of
the genome of vertebrates, fungi and plants and
are highly variable in array size. The number of
repeats for a given minisatellite may differ
between individuals.  This feature is the basis
of DNA fingerprinting. Microsatellites are
moderately repetitive, and composed of arrays of
short (2-6 bp) repeats found in vertebrate,
insect and plant genomes. The human genome
contains at least 30,000 microsatellite loci
located in euchromatin. Copy numbers are
characteristically variable within a population,
typically with mean array sizes on the order of
10 to 100. Huntingtons triplet of CAG causes
many glutamines to be coded into the protein
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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