Gene Transcription Flashcards
What is the name for genes transcribed in all cells?
Housekeeping genes
How many types of RNA Polymerase are there?
3
Which types of RNA do each type of RNA polymerase transcribe?
I: rRNA
II: mRNA
III: tRNA and 5S RNA
What are the proteins that bind to DNA to regulate transcription?
Transcription Factors
What is the template strand also known as?
What does this mean?
Antisense Strand
The DNA that gets transcribed: anti as its the opposite of the RNA transcribed. Complimentary to sense strand - the coding strand
Describe the basic structure of transcription.
- DNA unwinds
- Ribonucleotides base pair with the antisense DNA template
- RNA Polymerase creates phosphodiester bonds between Ribonucleotides in the 5’ to 3’ direction
What are the two types of transcription factors?
Transcriptional activators: upregulation
Transcriptional repressors: downregulation
What is the initiation step
The construction of a transcription complex at the gene promotor before transcription can begin
What is the specific DNA sequence that marks the point of initiation for RNA Pol II
TATA
What is the basal transcription complex? (BTC)
The complex that produces a low level of transcription in the absence of other factors
What is the effect of the basal transcription complex on RNA Pol?
Alloes RNA Pol II to be phosphorylated and commence transcription
What is the first step of formation of the BTC
TF IID (TATA binding protein) binds to TATA. Partially unravels DNA, and widens minor groove for increased base contact.
How is unidirectional transcription achieved.
DNA is unwound asymmetrically.
What is the second step of the BTC formation?
TF IIA and IIB bind to IID.
What does TF IIB do?
Binds to RNA Pol II and TF IID
Which other Transcription factors bind to RNA Pol II?
TF IIF, IIE, IIH, IIJ
What do TF’s actually do?
Bend DNA on binding making transcription possible/easier.
Name the letters of all the TF II’s involved in the BTC
D,A,B, F,E,H,J
“Dab Jehf, Dab!”
What do transcription factors also do to change the expression of genes?
Modify chromatin by recruiting proteins with enzymatic activity that modify histones
How do TF modify histones?
Hyperacetylation: DNA exposed, gene expressed
Hypoacetylation: DNA hidden, gene repressed
What do mutated/abnormal TFs lead to?
Cancer
Which factors effect Transcription factor expression?
Cell lineage
External signals: Hormones, growth factors, mechanical stress
What is the primary transcript known as?
pre-mRNA
or
Heterogenous nuclear RNA (hnRNA)
How are eukaryotic genes coded in DNA?
Discontinuously in Exons w/introns in between
How is the primary transcript processed, and where?
Introns are cleaved out in the nucleus.
What is the name of the location where the end of an exon is cleaved from the intron?
Splice donor site
last 2 bases of exon and GU of intron
What is the name of the location where the end of an intron is cleaved from an exon?
Splice acceptor site
15 pyrimidine bases, any base then CAG (Pyr15NCAG)
Which bases mark the end of introns and exons?
AG
Which bases mark the beginning of an intron?
GU
What does mRNA processing require?
snRNP’s
Small ribonuclear proteins
Which snRNP binds to the splice donor site?
U1
Which snRNP binds to the splice acceptor site?
U5
Which snRNPs bind to the middle of the intron?
U2, U4, U6
What is the name of the complex that forms from binding of snRNPs?
Spliceosome
What does U1 do?
Cleaves splice donor site
What happens to the GU at the beginning of spliced intron?
Forms phosphodiester bond with branchpoint in the middle of intron
What does U5 do?
Cleaves splice acceptor site
What is the stucture of the cleaved intron called?
Lariat structure
What happens to the cleaved intron?
It is destroyed
What happens to two adjacent exons of mRNA?
They are ligated by RNA Ligase into a continuous sequence
What are the Post-transcriptional modifications of mRNA?
5’ Capping
3’ Poly-A tail
What happens in 5’ capping?
A phosphate is removed from the 5’ end of mRNA.
This is joined to GMP forming a 5’-5’ phosphate linkage.
The 7’ carbon in guanine is methylated.
7-methylguanylate cap
What is the function of a 5’ cap?
To protect the mRNA from exonuclease activity.
Allow recognition by ribosomes and increased translation.
What virus causes removal of caps preventing protein synthesis in infected cells?
Polio
How long is the Poly-A tail?
10-200 bases
What is the function of the Poly-A tail?
To stabilise the mRNA
A’s removed after translation, to monitor age of mRNA, and prevent translation of damaged mRNA
