Chapter 17 Flashcards
Eukaryotic Gene Regulation
- Each gene has its own promoter and is transcribed separately
- DNA MUST unwind from the histone proteins (wrapped around the DNA) before transcription
- transcription and translation are separated in TIME and SPACE
DNase I hypersensitivity
Hypersensitive sites: more open chromatin configuration site, upstream of the transcription start
site
Histone Modificaiton
− Addition of methyl groups to the histone protein tails
− Depending on which area is methylation – either activation or repression
- Addition of acetyl groups to histone proteins
− Associated with activation
Modifies the expression of the genes
DNase 1 function
Unwinds DNA
Chromatin remodeling complexes
Remodeling by repositioning the nucleosomes, initiating transcription because physically moving the nucleosome exposes the binding site (promoters) for transcription factors and RNA polymerase to bind
Nucleosomes
A length of DNA coiled around a core histone (protein wrapped around DNA)
The structure made up of histone and the DNA wrapped
DNA
- electronegative due to phosphate and backbones
Histones
Electropositive
Protein that wraps around DNA
Making them MORE electropositive —> tightens DNA around it —> DECREASING TRANSCRIPTION because it is more tightly bound and unable to transcribe (and vise versa)
Acetylation of histone proteins
Alters chromatin structure and permits some transcription factors to bind to DNA
Chromatin Remodeling
Chromatin-remodeling complexes: bind directly to DNA sites and reposition nucleosomes
DNA methylation
DNA Methylation
Methylation of cytosine bases adjacent to guanine nucleotides (CpG) “CpG islands”
Chromatin Immunoprecipitation Sequencing
Used to identify DNA binding sites of specific protein and the locations of modified histones proteins
Transcription Factors
Stimulate and stabilize basal transcription apparatus at core promoter
Mediator
Enhancers
DNA sequence stimulating transcription at a distance away from the promoter
DNA loops over and activating transcriptase apparatus
Silencers
DNA sequence with an inhibitory effect on the transcription of distant genes
Position and orientation independent, have binding sites for T.F.s to decrease transcription
Insulator
DNA Sequence that blocks or “insulates” the effect of enhancers by looping DNA sequences together
Creates its own neighborhood, pinched off, stopping the effects of other enhancers for
Regulation of Transcriptional Stalling and Elongation
RNA polymerase may pause of stall downstream of the promoter: heat shock genes are stall until heat stress is encountered (car in neutral, ready to go, THINK: start box)
Affected by regulatory factors
Response Elements
Common regulatory elements upstream of the start sites of a collective group of genes in response to a common environmental stimulus
MREs
Multiple response elements
Found in upstream region of the metallothionein in gene
Gene Regulation through RNA Splicing
– Eukaryotic genes can be regulated through the
control of mRNA processing.
– The selection of alternative splice sites leads to the production of different proteins.
● Alternative splicing in Drosophila sexual development
Alternative splicing of tra pre-mRNA
Two alternative 3’ splice sites are present
A way to regulate gene transcription
Degradation of RNA
- 5’ cap removal
- shortening of the polyA tail
- degradation of 5’ UTR coding sequence, and 3’ UTR
Small interfering RNAs and micro RNAs
Dicer
Cuts up RNA to produce single stranded siRNAs, short, which combine with proteins to form a RISC
RISC
Silencing complex, silence mRNA, not allowing mRNA to be translated.
Mechanism of gene regulation by RNA inference
RNA cleavage
Inhibition of translation
Transcriptional silencing
Slicer-independent degradation of mRNA
RNA Cleavage
RISC containing an si RNA, pair with mRNA molecules and cleave mRNA
Inhibition of translation
MiRNAs bind to mRNA, translation not allowed
Transcriptional silencing
Altering chromatin structure
STRUCTURE CONTROLS FUNCTION
Methylates attracted to specific histone tails when small RNAs bind to DNA
slicer independent degradation of mRNA
MiRNA attract dicer and RISC to cleave mRNA
SLICER AND DICER
Factors that impact the rate of translation
- availability of ribosomes
- charged tRNAs
- initiation & elongation factors
More ribosome binding when there are more initiation factors, there is more translation happening
Operon
Several genes controlled by one promoter in bacteria, more complex process in eukaryotes
