n4.19 eukaryotic gene regulationgene regulation results in differential gene expression, leading to...
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EUKARYOTIC GENE REGULATIONGene regulation results in differential gene expression, leading to cell specialization.
More Complex ControlsEukaryotes control gene expression at all levels of the process, from pre-transcription to post-translation.
Chromosome Structure• Chromosomes are densely packed
double-stranded DNA molecules (with hundreds of millions of base pairs). Chromosomal proteins help mediate this packing.
• Chromatin – Complex of DNA and proteins that make up the chromosomes
Access to DNAMost of the DNA in a eukaryotic cell is unavailable for transcription.The addition/removal of acetyl groups from the histone proteins that DNA is wound around leads to tighter or looser “packing” of the DNA.• Heterochromatin: more tightly packed
DNA, unavailable for transcription.- Acetyl Groups+ Methyl Groups
• Euchromatin: less tightly packed DNA, available for transcription.
+ Acetyl Groups- Methyl Groups
Pre-transcriptional controlsEukaryotes control transcription by controlling the transcription factors (proteins) present in the cell.
Control of Transcription Factors Major way that cells accomplish differential gene expression allowing for differentiation of cells
Post-Transcriptional/Pre-Translational ControlsFollowing transcription - 5' capping and 3' poly-A tails are necessary
Eukaryotic mRNA’s are extensively processed after being transcribed.“alternate splicing”: combining different exons in a transcript to produce multiple functional transcripts.
• Exons - kept• Introns - removed
RNA Interference (RNAi): micro RNA’s are produced that bond with specific transcripts and block translation.
Post-Translational ControlsProtein targeting: signal sequences on polypeptides will target the production of the polypeptide into the cytoplasm or into the endomembrane system.
Protein Activation & DegradationProteins for certain cellular pathways are made in inactive forms that are only activated when specific signals are received.
Proteasomes: organelles that target and destroy proteins that have been “tagged” to be degraded in the cell.