LT6: RNA processing Flashcards
What’s the most abundant RNA?
Ribosomal RNA
Who synthesizes pre-rRNA
RNA polymerase I
Pre-RNA is processed where and to generate what
In the nucleolus
Generates the 28S, 18S, and 5.8S
In the processing of rRNA, it is cleaved by who?
It’s cleaved by ribonucleases (RNase)
In the processing of pre-rRNA, it is trimmed by….
Exonucleases
In the processing of pre-rRNA l, base and sugar modification is carried out by…..
Small nucleolar RNAs (snoRNA)
In transfer RNA, a 16 nucleotide sequence is cleaved by…
RNase P (ribozyme)
In transfer RNA, a 14 nucleotide intron in the anticodon loop is removed by….
Nucleases
In tRNA, uracil residues at the 3’end are replaced by what sequence
The CCA sequence
Where can you find the CCA sequence
It’s found in all mature tRNA
What does RNA polymerase II synthesizes
It synthesizes the primary RNA transcript called heterogeneous nuclear RNA (hnRNA)
What does the hRNA undergoes in the nucleus
Undergoes extensive co-post transcriptional modification
The modifications that hRNA undergoes in the nucleus are
- 5’capping
- 3’ poly A tail addition
- Removal of introns (splicing)
What is the component of “cap”
7-methylguanosine
Where is cap added
It’s added backward in a 5’-5’ triphosphate linkage
Addition of GMP IN cap is by who?
Guanylytransferase
Cap methylation is catalyzed by..
Guanine -7 methyltranferase
Added to the nitrogen #7
What are the function of capping
- Aids in mRNA stabilization
2. Facilitates initiation of translation
What is the polyadenylation signal sequence
AAUAAA
What is cleaved after the PSS siganl
The Hn- mRNA
The 40-200 adenine (A) nucleotide are added to which end
Added to the 3’end
The A nucleotide are catalyzed by…
Polyadenylate polymerase (poly A pol) -atp is used as a substrate
The poly A tail sequence is not transcribed from where
From the DNA
What are the function of the addition of 3’poly A tail
- Facilitates mRNA transport out of the nucleus
- Stabilizes the mRNA
- Aids in translation
What is splicing
It’s the removal of introns (non-coding sequence) and joining of exons (coding sequence) to form the mature mRNA
What is the structure of intron
- 5’ splice site : 5’ GU 3’
- 3’ splice site : 5’ AG 3’
- branch point A
In any kind of mRNA, whenever there’s an intron, it always start with what and ends with what
- Starts with GU
- ends with AG
- has a branch site in the middle
What are the 2 mechanisms of splicing
SnRNPs
The splicesome
What does snRNPs stands for
Small nuclear ribonucleoprotein
SnRNPs consists of
Small nuclear RNAs (snRNA) associated with nuclear proteins
SnRNPs aids in what?
They aid in splicing
What is the molecular complex that accomplishes the splicing mechanism
The spliceosome
How many % of all genetic diseases are a result of mutations that affect RNA splicing
15%
What is Beta(0)- thalassemia
- It’s a homozygous mutations that totally abolish normal splicing
Beta(0)- thalassemia happens in which junction sequence
In the 5’-3’ intronic splice junction sequence of the hemoglobin gene
What is beta(+) thalassemia
It’s a point mutation that changes the sequence in the polyadenylation signal site of the hemoglobin gene from AAUAAA to AACAAA
