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Molecules and Energetics Block 1 > RNA Processing > Flashcards

RNA Processing Flashcards

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1
Q

What are the 3 steps in mRNA processing?

A
  1. Capping of 5’end of pre-mRNA
  2. Polyadenylation of the 3’ end of pre-mRNA
  3. Splicing of Pre-mRNA
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2
Q

What is the name of the enzyme that adds GTP to the 1st nucleotide of pre-mRNA? And what kind of unique bond does it form?

A

1) Guanylyltransferase (capping enzyme)

2) 5’-5’linkage

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3
Q

When does the capping rxn occur?

A

Immediately after the 1st phosphodiester bond is formed

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4
Q

What is the role of methyltransferaces in the capping of the 5’end of pre-mRNA?

A

Methylation of N-7 on the terminal guanine and the 2-OH on riboses of the next 2 nucleotides.

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5
Q

What is the function of 7-methylguanosine cap?

A

1) Required for initiation step of translation

2) Enhances stability

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6
Q

What is the polyadenylation sequence in the 3’end of pre-mRNA?

A

AAUAAA in the 3’-UTR last exon

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7
Q

What is the name of the enzyme that recognizes and cleaves the 3’end for polyadenylation?

A

Cleavage and Polyadenylation Specificity Factor

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8
Q

What enzyme add the poly A tail to the 3’end?

A

PolyAPolymerase

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9
Q

What are the functions of the polyA tail?

A

1) Binding sit for PolyA Binding Protein
2) mRNA stability
3) Regulation of initiation step of translation

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10
Q

What are the components of a splicesome?

A

Pre-mRNA (hnRNA) and snRNPS (small nuclear ribonucleoprotein particles)

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11
Q

What consensus sequence is at the donor 5’ splice site?

A

GU

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12
Q

What is the consensus sequence at the acceptor 3’ splice site?

A

AG

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13
Q

What is the mechanism for the splicing reaction?

A

1) First cleavage-ligation reaction (transesterification): 2’OH-A from branch site cleaves the GU on the 5’donor site
2) Second C-L rxn (transesterfication): -OH from 5’ attacks A-G on the 3’ end

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14
Q

What is a product of splicing?

A

Lariat

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15
Q

What is the unique bond that forms btw branch site A in the intro and the 5-end donor site of the intron?

A

2’-5’ phosphodiester bond

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16
Q

What is the function of U1 snRNP?

A

Pairs with donor 5’ splice site of pre-mRNA

17
Q

What is the function of U2 snRNP?

A

Pairs with A-branch site; one of the components of the ribozyme

18
Q

What is the function of U4?

A

Interacts with U6 snRNP

19
Q

What is the function of U5?

A

Pairs with 3’ acceptor site; aligns splice sites for catalysis by ribozyme.

20
Q

What is the function of U6?

A

Displaces U1 at 5’ splice site

Forms with U2 the ribozyme

21
Q

What are the two snRNPs that form the ribozyme to catalyze splicing reactions?

A

U2 and U6

22
Q

What are the 2 main roles of enhancers and silencers?

A

1) Regulate splicing at specific exon-intron boundaries

2) Enable correct splice sites in pre-mRNA to be distinguished from cryptic splice sites

23
Q

What is the function of Exon Splicing Enhancers (ESE) and Intron Splicing Enhancers (ISE)?

A

Cis-acting elements that facilitate recognition of an exon by the splicesome

24
Q

What is the function of Exon Splicing Silencers (ESS) and Intron Splicing Silencers (ISS)?

A

Cis-acting elements that DO NOT facilitate recognition of an exon by the splicesome.

25
Q

Do they type, #, and position of cis-acting elements (e.g. silencers and enhancers) vary at each exon-intron junction within each pre-mRNA?

A

YES

26
Q

What is the generation of differenct mRNAs from the same pre-mRNA by splicing exons together in different combos?

A

Alternative splicing

27
Q

What is B+-thalassemia?

A

Partial reduction in synthesis of B-hemoglobin chains; a hereditary anemia that results from a splicing defect

28
Q

What is B0-thalassemia?

A

No synthesis of B-hemoglobin chains; a hereditary anemia that results from a splicing defect

29
Q

What is the effect of a splicing error?

A

A frameshift results in a non-sense mutation bc the reading frame contains a stop-codon so the mRNA of B-hemoglobin degrades and the protein isn’t produced.

30
Q

What is RNA editing?

A

Change in the nucleotide sequence of RNA by a process other than splicing

31
Q

Give an example of RNA editing?

A

Deamination results in a different base. E.g. small intestine C to U shorted form of Apo-B-100 protein

Molecules and Energetics Block 1 (4 decks)

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