Chapter 3 Flashcards
What are the steps of transcription?
- Transcription factor binds to the TF-response element
- RNA polymerase binds to TATA-box
- Transcription starts
What is a response element?
Specific DNA sequences that can be recognized by transcription factors
What domins do all Transcription factors have?
- DNA-binding domain
2. Transcriptional activation domain (binds to Polymerase II)
What do some TFs have, but not all?
- Dimerization domain
2. Ligand-bindng domain
What kinds of DNA binding domains are there?
- Zinc finger
- Helix-loop-helix
- Helix-turn-helix
- Leucine zipper
What is the role of Ligand-binding domains?
it is a mechanism to regulate the activity of TFs. Some TFs repress transcription in the absence of some ligands
What is the role of TF dimers?
Dimers can have various combinations of transcriprion factors, giving rise to different activation properties
What technique could be used to study TF binding to DNA?
EMSA (Electrophoretic mobility shift assay)
- Difference between DNA/protein complex and free probe
What kind of modifications can histones undergo?
- Acetylation
- Methylation
- Phosphorylation
- Ubiquitination
Are histone modifications reversible?
Yes
What effect does acetylation have on gene transcription?
Activatory effect
what effect does methylation have on gene transcription?
Repressing effect
What kind of histone modification can promote cancer?
- High HDAC (histone deacetylase) activity found near tumor-suppressor genes
- High HAT (histone acetyl transferase) activity found near oncogones
What effect does methylation have on DNA?
Repressing effect
Where does methylation of the DNA happen?
In a C preceding a G on a strand. There are CpG islands near gene promoters that can be methylated.
How does DNA methylation inhibit transcription?
- Prevent TFs from binding to the DNA
2. Recruits HDAC to remove acetyls from histones and make chromatin more compact
Which enzyme transfers methyl groups to DNA?
DNMT (DNA methyl transferase)
What is the role of miRNA?
It is a post-transcriptional regulator of gene expression
How does miRNA control gene transcription?
- Repressing translation
2. destabilisation and cleavage of mRNA
what is the function of a T-loop?
A T-loop is used to prevent the DNA endings from being seen as strand breaks.
what are the components of a telomerase?
hTERT and hTR
Which cells normally express telomerase?
Embryonic stem cells and germ line cells
what could be a reason for telomere shortening?
- End replication problem
2. Oxidative stress
What are some challenges in targeting telomerase a sa therapeutic option
- Inhibitors of this enzyme are very rare and toxic
- Cancers might have already produced cells with long telomers, so division can still go on for some time
- Cancer cells may be resistant to the telomerase inhibitors
