W1 RNA synthesis Flashcards
Gene
- Unit of heredity; contains instructions for OGs PT
- DNA segment containing instructions for making a
particular product - including regulatory elements
Centromere
Primary constriction, repeats of DNA. Keeps CS to spindle so daughter cell has one copy only
Telomere
End of CS, cell joins and loops as telomere is on one end. Protects end and no gene end of CS lost
Intergenic region/sudo genes
IR = almost all DNA Sudo = duplicates of non functional DNA
Why is RNA single stranded
So can form intraM base pairs + fold into specific structures
Transcription
- DNA unwound + bases exposed → one DNA strand
acts as template and ribonucleotides added → RNA
complementary to DNA strand - Incoming ribonucleotide linked to growing RNA chain
by RNA P (covalent) - RNA does not remained H bonded to template →
RNA chain displaced and DNA helix reforms - Energy provided by incoming ribonucleoside
triphosphates (ATP, CTP, UTP and GTP) - RNA polymerase do not need a primer → error =
1/10^4 - Unwinds small portion of DNA + synthesis in 5’ to 3’
Pre transcription
- Transcription factor TFIID binds to a part of the
promoter called TATA (located 25 nucleotides
upstream from transcription site) through TBP (TFIID +TBP = 10 different proteins) → TFIIA
stabilises complex → local distortion caused in double
helix - Other factors assemble (TFIIB,TFIIF, TFIIE) along
w/RNA PII to complete
transcription initiation complex - Addition of phosphate groups (tail of RNA PII) to
release RNA PII initiated by TFIIH (has protein kinase)
→ TF dissociate from DNA - After transcription RNA PII stripped of phosphates by phosphatases (only dephosphorylated RNA PII can initiate transcription)
Transcription factor regions
2 functional regions:
- DNA binding domain = 2 AAs that recognise specific
DNA bases on regulatory element - Activator domain
Proximal control elements
GC box (GGGCGG) → 100 bp upstream (position/orientation dependent) CAAT box (GGCCAATCT) → 80 bp upstream (followed by conserved consensus sequence)
Distinct patterns of nucleotides w/consensus sequences occurring upstream initial transcription site → signals binding site for RNA TF + accompanied by these consensus sequences
UTR
Transcribed not translated
5’ UTR: regulation of translation
3’ UTR: mRNA stability + miRNA binding
RNA capping
- 5’ modification
- Addition of an atypical nucleotide (guanine nucleotide
w/methyl group at C7 + 5’-5’ TP bridge) attached to 5’
end of RNA in an unusual way - Capping after RNA PII produced 25 nucleotides
Polyadenylation
- New mRNA w/special structure at it’s 3’ end
- Poly-A-tail usually a few hundred nucleotides long
- RNA chain first cut at specific signal sequence by specific endonuclease + second enzyme adds
repeated A nucleotides to cut end
+:
- Increase stability
- Facilitate export to CT - Checked before translation
Splicing
- Carried out largely by RNA molecules = snRNAs, are
packaged w/add. proteins forming small nuclear
ribonucleoproteins snRNPs - Pyrimidine rich region (especially uracil) promotes
assembly of spliceosome, located about 5-40 bp
before 3’ end of intron to be spliced - snRNPs → recognise splice-site sequences by CBP
b/een RNA and pre-mRNA → form
core of spliceosome - Spliceosome cuts at cleavage signal by forming a lariat
structure leading to ligation of exons - Alternative splicing allows different proteins to be
produced from same gene → ↑ eukaryotes coding
potential of genomes - Exon skipping ~ 95% genes
Exporting from nucleus
Highly selective
Mediated by nuclear pore complexes
Must be bound to appropriate set of proteins (cap-binding complex, transcription-coupled export complex + exon-junction complex)
mRNA eventually degraded in cytosol
