Introns & splicing Flashcards

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1
Q

What are Introns?

A

a nucleotide sequence whcih is REMOVED during mRNA splicing and is not present in mature mRNA

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2
Q

What are Exons?

A

protein coding nucleotide sequences that are are NOT REMOVED during mRNA splicing and are still present in mature mRNA

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3
Q

where are introns found?

A

tRNA,mRNA,rRNA

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4
Q

WHat are the 4 groups of Introns?

A

Group I, Group II, splicesome-dependant Introns, Nuclear tRNA Introns.

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5
Q

What is conserved between all Intron groups?

A

5’ and 3’ splice site

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6
Q

What is unique to Group 2 and splicesome-dependant Introns?

A

branch site

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7
Q

How do Group I Introns undergo splicing?

A

Self-splicing using Co-factor of guainine or similar (G,GMP,GDP,GTP).

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8
Q

What type of enzyme does RNA act as during splicing?

A

ribozymes

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9
Q

What is the universal method of splicing between the first 3 groups of introns?

A

Transesterfication - the exchanging of organic R’ groups of alcohol with another organic R’ group of an ester, to form two different alcohol and ester.

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10
Q

What is the mechanism for splicing in Group I introns?

A

3’-OH of the CO-Factor acts a nucleophile and attacks the 5’ splice site, binding to it and seperating the upstream exon from the intron.

THe 3’-OH of the upstream exon acts a nucleophile attacking the 3’splice site of the downstream , which fuses the two exons.

leaving the Intron.

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11
Q

What occurs to Introns after splicing ?

A

they fold into a tertiary structure and degrade.

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12
Q

What is the difference in mechanism between Group I and Group II introns?

A

Group I introns use external Co-Factors , using the 3’-OH of a G molecule.

Group II, does not have a Co-factor, instead uses 2’-OH of adenine on the BRANCH SITE.

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13
Q

What is the mechanism for splicing in Group II Introns?

A

2’-OH on adenine on the BRANCH SITE acts as a nucleophile and attacks the 5’splice site, forming a LARIAT structure( A has 3 phosphodiester bonds, one being a 2’-5’) and seperating he upstream exon from the intron.

The 3’-OH of the guanine on the upstream exon acts a nucleophile and attakcs the 3’ splice site, fusing the two exons.

leaving the intron in its Lariat form.

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14
Q

What are the conditions for self splicing in Group II introns?

A

in vitro - high [salt]
otherwise in vivo they require enzymes, Maturase, which some produce.

Group I introns also produce maturase to increase efficiencey of splicing.

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14
Q

What does the presence of Group I and II introns in mitochondria in plants and animals, say about transcription in Bacteria

A

Mitochndria thought to have bacterial orgin, but are in fact then processed,

HOWEVER, this is self splicing.

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15
Q

What is the Intron- early Hypothesis

A

That the existence of introns in all 3 domains of life means theyre ancient.
and their maintenence in modern organism means theyre valuable.

16
Q

What is the Intron-Late Hypothesis?

A

some group I Introns encode for homo endonucleases which provide mobility for introns, allowing them to move between locations and organism

Parastic nucleic acid./

17
Q

What does snRNP stand for

A

small nuclear ribonucleic particle

18
Q

What is the only difference between Group II and splicesosome-dependant splicing

A

splicesosome-depenedant splicing uses splicing factors, called snRNPs which include:
snRNA and at least 7 protein subunits

19
Q

What is the mechanism for splicesome-dependant splicing?

A

U1(type of snRNP) bind to the 5’ splice site, U2 binds to the branch site,

This is follwed by a preformed U4-5-6 to associating with the complex, remaining inactive.

The dissocociation of U4 activates U6, which displays U1.

it then undergoes the same splicing order as a Group II intron.

20
Q

Why does U4 innactivate U6 in splicosome-depenedant

A

the base pairing between U4 RNA and U6 RNA .

21
Q
A