Transcript Eukaryotic Gene Expression

Eukaryotic Gene Expression
• Why is gene regulation more complex in
eukaryotes than prokaryotes?
• Eukaryotes have larger more complex
genome
• Eukaryotic DNA must be more highly
organized than prokaryotic DNA
Prokaryotic vs. Eukaryotic DNA
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Prokaryotic DNA
circular
smaller than
eukaryotic DNA
associated with very
few proteins
less structured and
folded
Eukaryotic DNA
• associated with lots of
histone proteins to
form chromatin fiber
• very extended and
tangled during
interphase
• condensed into
discrete chromosomes
during mitosis
Eukaryotic Development
• Cellular differentiation is the
specialization of cells during
development
• Since all cells have the same DNA, how
can differentiation occur?
• Gene regulation.
Selective Gene Expression
• How do cells
become
specialized?
• Different genes
are activated at
different times
during
development.
• Each cell utilizes
only about 3% of
genome
DNA Packing
Helps regulate gene
expression
• DNA in one human cell’s 46
chromosomes would be 3 meters long.
• How, then, does it all fit into the nucleus?
• DNA packing
• Why do densely packed regions of
chromosomes inactivate gene
expression?
• RNA pol can’t get to the gene for
transcription.
• What is the difference between
heterochromatin and euchromatin?
• Heterochromatin remains highly
condensed even during interphase
• Barr bodies are X chromosomes
condensed into heterochromatin
• Telomeres, centromeres also
heterochromatin
• euchromatin is chromatin that is not
condensed and can be transcribed
Control of Gene Expression
• What are the steps from chromosome to
functional protein?
• Unpacking Transcription mRNA
processing  export from the nucleus
 translation  protein modification
• ANY of these steps can be regulated in
eukaryotes
Control of
Gene
Expression
Chromatin modification
• DNA methylation; the addition of methyl
groups to DNA
• essential for inactivation of the DNA
– Inactive genes in a cell are methylated
– Epigenetic memory due to methylating enzymes
that methylate the new daughter strand the same
as the parent strand.
• Can be passed on in repro
• Histone acetylation is the attachment of an
acetyl group to histone proteins
• acetylation increases likelihood for
transcription of the DNA
Transcriptional Control
• Transcription factors allow RNA pol to
find the promoter region
• association between transcriptional
factors and enhancer or promoter
region regulates gene expression
Posttranscriptional control
• Regulation of RNA processing
• Regulation of mRNA degradation
– Can last from hours to weeks
• Regulation of translation
– initiation sequence can be blocked
Protein Degradation;
posttranslational control