Transcript Chapter 19 Organization and Control of Eukaryotic Genomes

Chapter 19 Organization
and Control of Eukaryotic
Genomes
…Or How To Fit All of the Junk In
the Trunk
Eukaryotic Chromatin Structure

Order of Chromatin Structure
DNA double helix
 Nucleosomes
 30-nm chromatin fiber
 Looped domains
 Folding of looped domains
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Details, Details, Details

Nucleosomes are made up of four
Histones. H2A, H2B, H3, H4
Histones are mostly postitivly charged amino
acids.
 DNA (negitivly charged is attracted to
Histones)


DNA is wrapped around the Nucleosomes
twice. An extra Histone (H1) Binds to the
DNA just after the Nucleosome.

Figure 3-D-2. Each
nucleosome consists
of 146 bp DNA and 8
histones: two copies
for each of H2A, H2B,
H3 and H4. The DNA
is wrapped around
the histone core,
making nearly two
turns per
nucleosome.
Even More Details!
30-nm Chromatin fiber—Coils of the Fiber
with the Nucleosome that forms folds that
are 30 nm in size
 Looped domains—30nm fiber folds and
attaches on to nonhistone protein scafold.
 When Chromatin is condensed into
chromosomes the looped domains coil
and form a tightly packed Chromosome.

Genome Organization at the DNA
Level

Repetitive DNA (non-coding)
Accounts for aprox 97% of human DNA
 Tandemly Repetitive DNA—Short sequences
repeted in a series.
 Can cause Genetic disorders.
 Typically found in centromeres and telomeres
so it is thought to be used for structure.
 Interspersed Repetitive DNA—Copies of
similar sequences but not repetitive.

Gene Change in Somatic Cells
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Gene Amplification—Selective replication
of specific genes.
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Example in egg cells increasing the amount of
rRNA will increase the number of ribosomes
which increases the protein output of the cell
when it is fertilized.
Transposons and Retrotransposons—DNA
that can move from one location to
another. RT utilizes RNA and reverse
transcriptase to move.
Gene Expression
Specialized Cells and tissues are selective
in the genes they express. Genes turned
on and off in response to signals.
 Pg 363 to see general overview of gene
expression.

Chromatin Modifications
Chromatin Modifications affect the gene
availability for transcription
 DNA Methylation—Attachment of methyl
groups (CH3) to DNA bases after DNA
synthesis.
 Inactive DNA is usually highly methylated
when compared to highly active
transcription regions of DNA.

More Modifications
Histone Acetylation—attachement of
Acetyl groups (COCH3) to amino acids of
histone groups. Deacetylation is the
removal of acetyl groups from histones.
 Histones that have been acelylated have a
looser bond with DNA and transcription
proteins have easier access to DNA.
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Left for you
Control elements and transcription factors
pg. 364-368
 Biology of Cancer pg. 369-372
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