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

Post Transcription Flashcards by Ahn Studies

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

heterogenous nuclear RNA (hnRNA)

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where is hnRNA processed

nucleus

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hnRNA is processed to mature into what

translatable RNA
functional rRNA and tRNA

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AUG in eukaryotes is not necessarily found in __

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post-transcriptional processing

minor processing
major processing

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minor processing events

RNA editing
base modification

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

RNA editing

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example of RNA editing

mitochondrial mRNA in trypanosomes
- insertion of one or more U

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covalent modification of a base within a molecule

base modification

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example of base modification

tRNA molecules

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in most tRNA molecules about __ of the nucleotides are modified

10%

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3 major mRNA processing events

capping
tailing
splicing

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addition of 5’ cap

capping

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what is added in capping

7-methylguanosine triphosphate

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addition of 3’ polyA tail

tailing

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removal of introns

splicing

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enzyme used in capping

guanylyl transferase

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function of capping

stabilizes and prevents degradation of the mRNA -> enhances translation
ribosome recognition

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how many As are added during tailing

up to 150 As

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enzyme used in tailing

polyA polymerase (nuclear)

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conserved sequence during tailing

AAUAAA

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purpose of tailing

improves translation efficiency and stability

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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

alternative tailing

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factors where alternative tailing depend on

developmental stage
location

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

splicing

percent removed during splicing

50-90%

spliced out during splicing

introns/intervening sequence

introns that are self-splicing

self-splicing group II introns (ribozymes)

what is processed in prokaryotes

- tRNA - rRNA

what are processed in eukaryotes

- tRNA - rRNA - mRNA

prokaryotes do not have __

introns

- have many genes, producing multiple proteins - only have one promoter - have coregulation - more efficient

polycistronic mRNA transcripts

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

monocistronic mRNA

structure of introns after it is spliced

lariat

splicing signals

1. 5' splice site 2. 3' splice site 3. branch point

5' splice site

GU at 5' end of intron

3' splice site

AG at 3' end of intron

Location of branch point

located about 30nt from 3' end

what does the branch point consist

one adenine

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

Chambon's rule

mutant splice sites

aberrant splicing

- large, nuclear RNA-protein complex - catalyzes RNA splicing

spliceosome

snRNA + protein

snRPS (small nuclear ribonucleoprotein particles)

5 snRNPS assemble to form what?

spliceosome

what are the 5 snRNPs

1. U1 2. U2 3. U4 4. U5 5. U6

size: U1

165

size: U2

185

size: U5

116

size: U4

145

size: U6

106

role: U1

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

role: U2

binds the branch site and forms part of the catalytic center

role: U5

binds the 5' splice site

role: U4

masks the catalytic activity of U6

role: U6

catalyzes splicing

first splicesomes to attach to intron

- U1 - U2

two-step slicing reaction

1. 1st transesterification reaction 2. 2nd transesterification

what happens during 1st transesterification reaction

- cleavage of 5' exon-intron boundary - formation of intron lariat intermediate

what happens during 2nd transesterification reaction

- joins two exons - release of introns

- a way of introducing diversity to the gene products of transcription - creates proteins/RNA from the same DNA sequence

alternative splicing

example of alternative splicing

- calcitonin mRNA (thyroid) - CGRP mRNA (hypothalamus)

- eukaryotes - exits nuclear pore

RNA transport

energy generation

ran protein

exportins and importins

karyopherins

there are at least how many human karyopherins

20 different human karyopherins

example of karyopherins

1. exportin-t 2. Importin β

for export of tRNAs in yeast and mammals

exportin-t

for import of snRNAs from cytoplasm into nucleus

Importin β

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

Yra1p

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

Aly

in bacteria, transcription is simultaneous with translation

coupled transcription-translation