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BIO107 - Cell and Molecular Biology > Post Transcription > Flashcards

Post Transcription Flashcards

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1
Q
  • primary transcript
  • contains exons and introns
  • processes in the nucleus to mature translatable RNA or functional rRNA and tRNA
A

heterogenous nuclear RNA (hnRNA)

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2
Q

where is hnRNA processed

A

nucleus

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3
Q

hnRNA is processed to mature into what

A
  • translatable RNA
  • functional rRNA and tRNA
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4
Q

AUG in eukaryotes is not necessarily found in __

A

+1

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5
Q

post-transcriptional processing

A
  1. minor processing
  2. major processing
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6
Q

minor processing events

A
  1. RNA editing
  2. base modification
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7
Q

change in the base sequence of an RNA after it has been transcribed

A

RNA editing

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8
Q

example of RNA editing

A

mitochondrial mRNA in trypanosomes
- insertion of one or more U

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9
Q

covalent modification of a base within a molecule

A

base modification

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10
Q

example of base modification

A

tRNA molecules

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11
Q

in most tRNA molecules about __ of the nucleotides are modified

A

10%

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12
Q

3 major mRNA processing events

A
  1. capping
  2. tailing
  3. splicing
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13
Q

addition of 5’ cap

A

capping

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14
Q

what is added in capping

A

7-methylguanosine triphosphate

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15
Q

addition of 3’ polyA tail

A

tailing

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16
Q

removal of introns

A

splicing

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17
Q

enzyme used in capping

A

guanylyl transferase

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18
Q

function of capping

A
  1. stabilizes and prevents degradation of the mRNA -> enhances translation
  2. ribosome recognition
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19
Q

how many As are added during tailing

A

up to 150 As

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20
Q

enzyme used in tailing

A

polyA polymerase (nuclear)

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21
Q

conserved sequence during tailing

A

AAUAAA

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22
Q

purpose of tailing

A

improves translation efficiency and stability

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23
Q
  • some transcripts have 2 or more polyadenylation sites
  • “choice” depends on factors such as developmental stage and location
  • variability of proteins at post-transcriptional level is generated
A

alternative tailing

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24
Q

factors where alternative tailing depend on

A
  • developmental stage
  • location
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25
Q
  • removal of segments (50-90%) from primary transcript
  • introns/intervening sequence are spliced out
  • generally follows tailing
  • caps retained, tailes sometimes removed
A

splicing

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26
Q

percent removed during splicing

A

50-90%

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27
Q

spliced out during splicing

A

introns/intervening sequence

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28
Q

introns that are self-splicing

A

self-splicing group II introns (ribozymes)

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29
Q

what is processed in prokaryotes

A
  • tRNA
  • rRNA
30
Q

what are processed in eukaryotes

A
  • tRNA
  • rRNA
  • mRNA
31
Q

prokaryotes do not have __

A

introns

32
Q
  • have many genes, producing multiple proteins
  • only have one promoter
  • have coregulation
  • more efficient
A

polycistronic mRNA transcripts

33
Q
  • one protein: one sequence
  • specific genes are turned on/off depending on cell needs, development, and environmental changes
  • independent regulation
A

monocistronic mRNA

34
Q

structure of introns after it is spliced

A

lariat

35
Q

splicing signals

A
  1. 5’ splice site
  2. 3’ splice site
  3. branch point
36
Q

5’ splice site

A

GU at 5’ end of intron

37
Q

3’ splice site

A

AG at 3’ end of intron

38
Q

Location of branch point

A

located about 30nt from 3’ end

39
Q

what does the branch point consist

A

one adenine

40
Q

introns begin with 5’-GU and end with 3’-AG

A

Chambon’s rule

41
Q

mutant splice sites

A

aberrant splicing

42
Q
  • large, nuclear RNA-protein complex
  • catalyzes RNA splicing
A

spliceosome

43
Q

snRNA + protein

A

snRPS (small nuclear ribonucleoprotein particles)

44
Q

5 snRNPS assemble to form what?

A

spliceosome

45
Q

what are the 5 snRNPs

A
  1. U1
  2. U2
  3. U4
  4. U5
  5. U6
46
Q

size:
U1

A

165

47
Q

size:
U2

A

185

48
Q

size:
U5

A

116

49
Q

size:
U4

A

145

50
Q

size:
U6

A

106

51
Q

role:
U1

A

binds the 5’ splice site and then the 3’ splice site

52
Q

role:
U2

A

binds the branch site and forms part of the catalytic center

53
Q

role:
U5

A

binds the 5’ splice site

54
Q

role:
U4

A

masks the catalytic activity of U6

55
Q

role:
U6

A

catalyzes splicing

56
Q

first splicesomes to attach to intron

A
  • U1
  • U2
57
Q

two-step slicing reaction

A
  1. 1st transesterification reaction
  2. 2nd transesterification
58
Q

what happens during 1st transesterification reaction

A
  • cleavage of 5’ exon-intron boundary
  • formation of intron lariat intermediate
59
Q

what happens during 2nd transesterification reaction

A
  • joins two exons
  • release of introns
60
Q
  • a way of introducing diversity to the gene products of transcription
  • creates proteins/RNA from the same DNA sequence
A

alternative splicing

61
Q

example of alternative splicing

A
  • calcitonin mRNA (thyroid)
  • CGRP mRNA (hypothalamus)
62
Q
  • eukaryotes
  • exits nuclear pore
A

RNA transport

63
Q

energy generation

A

ran protein

64
Q

exportins and importins

A

karyopherins

65
Q

there are at least how many human karyopherins

A

20 different human karyopherins

66
Q

example of karyopherins

A
  1. exportin-t
  2. Importin β
67
Q

for export of tRNAs in yeast and mammals

A

exportin-t

68
Q

for import of snRNAs from cytoplasm into nucleus

A

Importin β

69
Q

for export of mRNA to their respective places in the cell of yeast

A

Yra1p

70
Q

for export of mRNA to their respective places in the cell of animals

A

Aly

71
Q

in bacteria, transcription is simultaneous with translation

A

coupled transcription-translation

BIO107 - Cell and Molecular Biology (18 decks)

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