Transcription Flashcards
What happens during DNA transcription
Small piece of the DNA (gene) acts as a template • Either strand of DNA can act as a template. • Brief complementary base pairing between template and incoming ribonucleotides. • RNA is synthesized 5’ to 3’ (just like DNA) but does not require a primer.
Types of RNA
messenger RNAs, ribosomal RNAs, transfer RNAs
What does each type of rna do?
mrna - code for proteins, short lived
rrna - forms core of ribosome structure and catalyze protein synthesis, live up to weeks
transfer rna - serve as adaptors between mrna and amino acids during protein synthesis, live up to weeks
How many rna polymerases are there and what do they do?
three. RNAP 1 transcribes most rRNA genes, RNAP 2 transcribes messenger RNA, RNAP3, transcribes tRNA genes.
How is prokaryotic transcription initiated
sigma factor recognizes promoter, causing RNA synthesis to begin.
Describe sequences and element and transcriptional start site.
BRE: B recognition element, has tf2B as transcription factor.
TATA: important promoter element, has tbp as transcription factor.
INR: initiator element, has tf2d as transcription factor, DPE: downstream promoter element, has tf2d as transcription factor.
Why is TATA box important
transcription factor binding causes distortion of TATA DNA, marking site of active transcription.
How is eukaryotic transcription initiated:
- TFIID- TBP which is part of TF2 bind TATA box
- TFIIB: recognizes BRE and positions RNA Polymerase at start
- TFIIF: Stabilizes TFIID/B/Polymerase
interactions, attracts TFIIE and TFIIH - TFIIE: attracts TFIIH
- TFIIH: unwinds DNA, phosphorylates Ser5 of RNA Pol CTD and releases polymerase from the promoter
Exons vs introns
exons are expressed and introns are removed
What changes occur during transcription?
5’ capping, RNA splicing, 3’ polyadenylation.
What does rna polymerase 2 do?
Phosphorylation of Ser5 alone recruits capping factors • Phosphorylation at Ser2 and Ser5 recruits splicing proteins
• Phosphorylation at Ser2 alone recruits 3’ end processing proteins
What does rna capping require?
Phosphotase, guanyl transferase, methyl transferase
What intron regions are recognized during splicing?
5’ exon 1, central adenine region, 3’ exon 2. exon 1 and exon 2 come together to form final mRNA
describe rna splicing
• Spliceosome is assembled as transcription occurs. • Steps:
- Adenine in intron attacks 5’ splice site.
- Cut 5’ end forms a loop.
- The free 3’OH end reacts with the 5’ end of the next exon, releasing a lariat.
what is involved in splicing?
Small nuclear RNA molecules (snRNAs) mediate key steps in splicing
• snRNAs complex with multiple protein subunits, forming small nuclear riboproteins (snRNPs)
• Spliceosome is formed by assembly of multiple snRNPs
