Eukaryotic Genomes 11 November, 2005 Text Chapter 19

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Eukaryotic Genomes11 November, 2005Text
Chapter 19
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Chromatin
In eukaryotes, DNA is present as several
different molecules. Each DNA molecule, along
with its associated proteins is one chromosome.
Chromosomes are in the extended conformation
while they are being transcribed. They are at
their most condensed during nuclear division.
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Regulation of Gene Expression
Changing the level of active protein to suit cell
type and environmental conditions is the goal of
gene regulation.
This regulation can occur at any of the steps in
gene expression. Regulation of transcription is
most common, important examples of each type of
regulation exist.
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Histone acetylation leads to derepressed
chromatin.
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Eukaryotic genes differ form prokaryotic genes in
several important respects. First, these genes
are never in operons. Each is transcribed
independently. Introns exist, and are spliced
out of the primary transcript. Finally, control
elements, the binding sites for transcription
factors, may be close to or far from the promoter.
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How can transcription factors bound to distal
control elements (activators) influence
transcription?
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Cell-type-specific Transcription
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Proteins recognize specific DNA sequences by
forming weak interactions between amino acids on
the protein and bases in the DNA molecule.
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Alternative Splicing
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RNAi
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Protein Degradation
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Cancer results from genetic changes that affect
the cell cycle.
These changes include abnormal activation of
oncogenes and inactivation of tumor suppressor
genes.
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Usually, a cancerous transformation in any cell
requires that several oncogenes be activated and
several tumor suppressors be inactivated.
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The genetic changes that cause colon cancer are
well understood.
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Eukaryotic DNA
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Replicative transposition and unequal crossing
over can lead to gene duplication
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Multigene families
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The globin gene family arose by duplication and
differentiation. Duplication can occur due to
unequal crossing over.
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Exon shuffling can lead to new proteins with
novel functions.
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