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

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 PackingHelps 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