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M2M Biochemistry and molecular biology > Pre-mRNA processing LO > Flashcards

Pre-mRNA processing LO Flashcards

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1
Q

What are the 3 major ways that mRNAs are processed?

A
  1. capping
  2. splicing
  3. cleavage/polyadenylation
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2
Q

what is capping?

A

addition of 7’methylGPPP cap to protect the exposed phosphate

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3
Q

what is splicing?

A

removal of introns by excision

ligation of exons together to make complete readable sequence

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4
Q

what is cleavage/polyadenylation?

A

removal of portion of 3’ end of by cleavage and then addition of polyadenosine tail to improve stability

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5
Q

what is pre-mRNA?

A

the primary transcript from DNA, needs to be processed before it can be translated, does not have 5’ cap or poly A tail. contains introns

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6
Q

what is mRNA in regards to pre-mRNA?

A

processed mRNA that is ready for translation into a protein

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7
Q

what binds the 5’ cap to the pre-mRNA?

A

cap binding proteins (CBP)

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8
Q

what is the functions of the 5’ cap?

A
  1. promote splicing of proximal intron to cap
  2. signal that mRNA is ready for export to cytoplasm
  3. prevent degredation of mRNA
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9
Q

what signals that mRNA is ready for degredation?

A

removal of the 5’ cap

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10
Q

what is the function of eIF4E?

A

(eukaryotic initiation factor 4E)

promotes translation initiation

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11
Q

what are the 3 steps required to place a 5’ cap to a pre-mRNA?

A
  1. triphosphatase removes gamma phosphate from 5’ end
  2. Guanylyltransferase adds GTP to terminal phosphate losing 2 phosphates from GTP in the process
  3. 7 nitrogen of guanine methylated by methyl transferase
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12
Q

what type of linkage is formed by guanylyltransferase?

A

5’ to 5’ linkage between phosphates of RNA and GTP

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13
Q

what is the methyl donor in the methylation of 7 nitrogen of guanine?

A

S-adenosylmethionine

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14
Q

what is the conserved consensus sequence in the 5’ end of an intron?

A

G U

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15
Q

what is the conserved consensus sequence in the 3’ end on an intron?

A

A G

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16
Q

what is the poly A site consensus sequence?

A

A A U A A A

17
Q

what is alternative splicing?

A

removal of different parts of a pre-mRNA to form different mRNA that will code for different proteins. Many pre-mRNA transcripts can code for multiple proteins but not until they are spliced at specific sites

18
Q

what are 2 diseases caused by splicing defects?

A
  1. marfans syndrome

2. spinal muscular atrophy

19
Q

what is the presentation of Marfan’s syndrome?

A

very tall stature, long limbs, protruding sternum, weakness or defects of the aorta and heart valves

20
Q

what type of inherited disease is Marfan syndrome in regards to genetics?

A

dominant autosomal disease

21
Q

Marfan is a result of disruption of splicing of which gene transcript?

A

fibrilin

22
Q

what is fibrilin?

A

component of connective tissues

23
Q

mutations of the splicing of the fibrilin gene interfers with the binding of which molecules?

A

U1 and U2 with snRNAs which regulate splicing causing marfans

24
Q

what is the function of U1 snRNA in splicing?

A

recognized the 5’ splice sequence by base pairing with it (base pairs between the exon and the intron)

25
Q

what is the function of U2 snRNA?

A

recognizes the branch point between introns and exons

26
Q

what causes recognition of exons by the splicesome?

A

binding of U1 snRNA with U2 snRNA upstream of exons

27
Q

what is a branch point on a pre-mRNA?

A

series of nucleotides between exons

28
Q

what are the 2 reactions that make the mature 3’ end of mRNA?

A
  1. cleavage: 20 bp downstream of AAUAAA is cut by endonuclease exposing 3’ hydroxyl group
  2. at 3’ OH, polyadenylation occurs
29
Q

what is the function of cleavage/polyadenylation specificity factor (CPSF)?

A
  • associated with RNA pol II and polyadenylate polymerase
  • when poly A tail gets around 250 bp long, polyadenylate polymerase cannot bind to CPSF anymore and this signals termination of RNA pol II from transcribing
30
Q

What are the 3 major functions of an mRNA’s poly A tail?

A
  1. makes mRNA stable and prevents premature degredation
  2. tail is bound by poly A binding protein (PAB I) which boosts translation in the cytoplasm by recruiting mRNA to ribosome
  3. signals for transport from the nucleus to the cytoplasm
31
Q

how does alternative poly A sites cause more than one protein to be made from a single gene?

A

early termination of transcript by addition of the poly A tail can leave exons from being transcribed thus making a different protein

32
Q

what is an example of different poly A sites resulting in different proteins?

A
  • IgM has 2 poly A sites

- MuS and MuM are 2 sites

33
Q

what type of IgM occurs from cleavage at the muS site?

A

antibody form that is secreted from plasma cells

34
Q

what type of IgM from cleavage at the muM site?

A

membrane bound antigen receptor on B cells

M2M Biochemistry and molecular biology (19 decks)

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