ch 17 Flashcards
Transcriptional regulation
Initiation of RNA polymerase
Splicing and cleaving
mRNA stability - 5’ cap; polyA tail
RNA editing
Translational control
preventing assembly of ribosome
breaking down the mRNA through microRNAs
Post-translational regulation
modifications to the amino acid sequence can modify the protein (i.e. protein phosphorylation)
Differences in Eukaryotic and Prokaryotic Gene Regulation
Eukaryotic - each structural gene has its own promoter and is transcribed separately; operons are not typical.
Chromatin structure affects gene expression in eukaryotic cells. DNA must unwind from the histone proteins before transcription.
Transcription and translation are separated in time and space due to the nucleus in eukaryotic cells
Eukaryotic gene regulation is less well understood than prokaryotic gene regulation – largely due to:
Larger genome
Sequence complexity
The difficulty of isolating and manipulating mutations for the study of gene regulations.
Chromatin structure itself represses gene expression:
For a gene to be transcribed, transcription factors must bind to the DNA.
Other regulator proteins & RNA polymerase must bind, too
chromatin-remodeling complexes
- transcription factors and other regulatory proteins that alter chromatin structure without modifying chemical structure of histones
-shifting things around to get where you need for tscript
Histone Modification
Histones have a globular domain that associates with the other histones and the DNA and also a positively charged tail that interacts with the negatively charged phosphate group on the DNA.
The tails are often modified by addition or removal of phosphate groups, methyl groups, or acetyl groups.
Addition of methyl groups to the histone protein tails:
Can bring about activation or repressing of transcription, depending on which histone is modified and which amino acids are methylated.
Histone methyltransferases add methyl groups to specific amino acids of histones (usually lysine or arginine).
Histone demethylases, remove methyl groups from histones.
Addition of acetyl groups
Normally stimulates transcription! opens things up allows tscript to take place
Acetylation alters chromatin structure and permits some transcription factors to bind to DNA.
DNA Methylation
Heavily methylated DNA associated with repression of transcription in vertebrates and plants
Abnormal methylation patterns also associated with some cancers.
Most common on cytosine bases adjacent to guanine nucleotides.
DNA regions with many CpG sequences are called CpG islands, and commonly found near transcription start sites.
Evidence indicates an association between DNA methylation and deacetylation of histones – both which repress transcription!
Epigenetics
– alterations to DNA and chromatin structure that affect traits and are passed on to other cells or generations but are not caused by changes in the DNA base sequence.
(i.e. chromo remod, hist mod, DNA methyl)
GAL4
– transcriptional activator protein that regulates transcription of several yeast genes whose products metabolize galactose.
Genes that control galactose metabolism are inducible (when galactose is absent, genes are not transcribed)
Transcriptional regulator proteins in eukaryotic cells acting as repressors, inhibiting transcription:
Bind to sequences in the regulatory promoter called silencers.
Unlike repressors in bacteria, most eukaryotic repressors do not physically block RNA polymerase.
Repressors here compete with transcriptional activators for binding sites on the DNA – and/or lock initiation of transcription through interference with basal transcription apparatus.
Enhancer
– regulatory elements that affect the transcription of distant genes (away from the promoter).
Enhancers often regulate genes in a cell type-specific manner (turn on different sets of genes for different cell types depending on the tissue)
