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71 Cards in this Set

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What is the central dogma for Eukaryotes?

(replication)DNA -->(transcription) pre-mRNA=> splicing=>mRNA(translation)--> protein

typical eukaryotic gene image look at

what is an exon?

coding sequence in eukaryotic

EX= exit the nucleus

what is intron?

the non-coding or intervening sequences in euk. genes

IN = stay w/in the nucleus

what is pre-mRNA?

the primary transcription of DNA

what is RNA splicing?

the process of introns being removed from the pre-mRNA.

What is spliceosome?

a complex of specialized RNA & protein subunits that removes introns from pre-mRNA

what is alternative splicing?

process of the re-combination of different exons in eukaryotes.

-Major source of genetic diversity of eukaryotes.

Describe RNA splicing?

-mRNA's contain different selection of eons can be generated from a given pre-mRNA.

Name the 3 classes of RNA splicing pathways?

1.) nuclear pre-mRNA splicing (spliceosome mediate intron removal)

2.) group 1 introns

3.) group 2 introns (intron itself folds into a specific conformation w/in the pre-mRNA & catalyzes the chemistry of released by itself and the exon ligation.)

How does the pre-mrNA splicing work?

there are 2 steps involved:

1.) 1st step: find the splice sites

2.) 2nd step: intron is moved in a form called Lariat through 2 transesterification reactions as the flanking eons are joined.

Name the splice sites in the first step of pre-mRNA splicing?

1.) 5' splice site

2.) 3' splice site

3.) Branch point site

what is 5' splice site?

boundary at the 5' end of the intron is marked by a specific nucleotide sequences (GU-AG law)

what is 3' splice site?

boundary at the 3' end of the intron is marked by a sequence.

what is brand point site?

sequence w/in the intron & is followed by a polypyrimidine tract (Py tract) rich in pyrimidine.

Sequences w/in the RNA deter time where what occurs?


Describe what is happening? 

Describe what is happening?

-GU 5' splicing site, AG in 3' splicing site & A in branch point site are the most conserved sequences & they are all in the intron.

-These sequences are important for the distinguish btw intron & exon, remove of intron, linkage of eons, & delineate where splicing will occur.

what step is this?

what step is this?

second step of pre-mRNA splicing

-Intron is removed through 2 trasesterificatiron reactions in a form called Lariat & the flanking eons are joined.

what happens in the trasesterirication reaction 1?

-part of second step

-2'OH attacks 5' site

-Result = the 5' exon is released

-5' intron forms a 3 -way junction

what happends in the transesterification reaction 2?

- THE OH of the 5' exon attacks the phosphoryl grp at the 3' splice site.

-RESUT: 5 ' and 3 ' exons are joined

-intron is liberated as a lariat

in the two transesterrification reactions, there is no what?

net gain in the number of chemical bonds, so no energy is demanded by the process

Why do we see a large amount of ATP being consumed during splicing reaction?

this is energy is required to properly assemble and operate the splicing machinery, not for the chemistry.

Splicesome is a complex of what?

specialized RNA & protein subunits

Splicesome comprises about how many proteins & RNA's?

150 proteins; 5 RNAs

Wha are small nuclear RNAs composed of?

Five RNAs ( U1, U2, U4, U5, U6, 100-300 nt)

The complexes of snRNA & proteins are called what?

snRNPS (small nuclear ribonuclear proteins

Spliceosome is the largest what?

snRNP, and the exact make up differs at different statnges of the splicing reaction

Spliceosome mediate what?s

splicing of introns from pre-mRNA

Many functions of the spliceosome are carried out by what?

RNA components

what are the 3 roles of snRNPS in splicing?

1.) recognizing the 5' splice site & the branch site

2.) bringing those sites together

3.) catalyzing the RNA cleavage

What are the 3 things that are important during splicing?



3.) protein-protein interactions

what is Nuclear Pre-mRNA splicing?

pathway medicated by splicesosome & involved in assembly, rearrangement & catalysis w/in the splicesome

What happens in step 1 of nuclear pre-mRNA splicing pathway assembly?

Step 1: U1 recognize 5 ' splice site

-one subunit of U2AF binds to branch site, former subunits interact w/ BBP & helps bind to branch point.

-Early (E) complex is formed

What happens in step 2 of nuclear pre-mRNA splicing pathway assembly?

Step 2:

-U2 binds to branch site and then A complex = formed

-Base-pairing btw the U2 & branch site is such that the branch site A is extruded. A residue is available to react w/ the 5 ' splice site.


What happens in step 3 of nuclear pre-mRNA splicing pathway assembly?

Step 3:

-U4, U5, and U6 form the trip-snRNP particle

-w/ the entry of the tri-snRNP, the A complex is converted into b complex


What happens in step 4 of nuclear pre-mRNA splicing pathway assembly?

Step 4:

-U1 leaves the complex, U6 replaces it at the 5' splice site

-U4 is released from the complex, allowing U6 to interact with

-U2: this arrangement called "The C Complex"

What happens in step 1 of nuclear pre-mRNA splicing pathway catalysis ?

step 1:

- C complex = active site, w/ U2 & U6 Rna's being brought together

-allows 5' splice accomplish Transesterificaiton 1

What happens in step 2 of nuclear pre-mRNA splicing pathway catalysis ?

Step 2:

-U5 SnRNP helps to bring the two exon together -allows second transeterification reaction,

What happens in step 3 of nuclear pre-mRNA splicing pathway catalysis ?

release of the mRNA product & snRNPS

image of step 1 nuclear pre-mRNA splicing assembly

image of step 1 nuclear pre-mRNA splicing assembly part two

image of step 2 nuclear pre-mRNA splicing assembly

image of step 2 nuclear pre-mRNA splicing assembly part two

image of step 3 nuclear pre-mRNA splicing assembly

image of step 4 nuclear pre-mRNA splicing assembly

image of step 1 nuclear pre-mRNA splicing assembly

image of step 2 & 3 nuclear pre-mRNA splicing assembly

image overview nuclear pre-mrNA splicing

what is self-splicing?

a few rare introns can remove themselves from pre-mRNA = self-splicing

what are the two classes of self-splicing?

Group I

Group II

what are the features of self-splicing?

-does not need spliceosome machinery

-Rna of intron mediates the chemistry of removal by intron itself folds into a specific conformation w/in the pre-mRNA and catalyzes the chemistry of released by itself & the exon ligation. (RNA enzyme endcoded by intron = riboenzyme)

what is group 1intron and group 2 intron in self-splicing?

-Group 1 intron self-splicing releases a linear introns rather than a lariat

-Group 2 intron self-splicing has the similar chemistry as the spliceosomemediated splicing

overview of 3 RNA splicing pathways

Features of alternative splicing?

-process of re-combination of different exon in eukaryotes

-many genes in higher eukaryotes encode RNA that can be spliced in alternative ways to generate 2 or more diff. mRNA's & diff. protein products (or isoforms)

-Microarry analyses = 40% drosophila & 75% human genes = alternative splicing

Alternative splicing is a major what?

source of genetic diversity in eukaryotes

Name the ways of alternative splicing can occur?

1.) Trans-splicing

2.) Two diff. mrNa's generate from a single gene = 2 diff. proteins

3.) mult. mRNA generated from a single gene = mult. proteins.

what is trans-splicing?

2 exon from diff. RNA molecules can be joined together.

-its generally rare, but it occurs in almost all of mRNA of trypanosome & nematode worm.

image of trans-splicing

image of singlee gene generate 2 alternate mRNA and thus 2 protein products

Eukaryotic pre-mRNA processing includes?

-5' capping

-5' structure

-5' capping targeting


what is 5' capping?

5' cap is specially altered nucleotide on the 5' end of precursor mRNA & some other primary RNA transcripts in eukaryotes.

-process of 5' capping is vital to creating mature mRNA - then able to undergo translation

The process of 5' capping generally serves four functions which are?

1.) regulation of nuclear export

2.) prevention o degradation by exonucleases

3.) promotion of translation

4.) promotion of 5' proximal intron excision

what is 5' cap structure?

5' cap is found on the 5' end of an mRNA molecule & consists of guanine nucleotied connected to the mRNA via an unusual 5' to 5' triphosphate linkage.

-Guanosine is methylated on the 7 position directly after capping by a methyl transferase.

Referred to as 7-methyl guanosine cap, abbreviatd m7G

what is 5' capping targeting?

- Capping ennzyme complex (CEC) required for 5' capping is

-As soon as the 5' end of the new transcription emerges the enzymes transfer to it and begin the capping process.

what is Polyadenylation - Poly A tail?

linkage of a polyadneylel + mRNA molecule.

-most mrNA molecules are polyadenylated at the 3' end of eukary.

What're are the 4 functions of Poly A tail?

1.) protect mRNA from degradation by exonucleases

2.) transcription termination

3.) export of mRNA from the nucleus

4.) mRna translation

image of the eukaryotic pre-mrNA processing

poly A procress

what happens in poly A the process?

-polyad. occurs during & immediately after transcription of DNA into RNA

-After transcription has been terminated, the mRNA chain is cleaved

-After mRNA has been cleaved, around 250 adenosine residues are added to the free 3' end at the cleavage site.l

-The reaction is catalyzed by polyaden polymerase

look at image

what happens in eukary mRNA export?

once processed (capped, intron-free & polyaden), MRNA is packaged and exported from the nucleus into the cytoplasm for translation

movement from the nucleus to the cytoplasm is an active and carefully regulated processes.

-the damaged, misprocesses & liberated introns are retained in the nucleus & degraded.

-a typical mature mRNA carries a collection of proteins including SR (serine-argenine rich protein) and another group of proteins binding specifically to exon-exon junctions that id's it absent mrRNA destined for transport

describe the pics.

describe the pics.

export takes places through the nuclear pore complex

-once in cytoplams , some proteins are discarded an are then imported back to the nucleus for another cyles of mrNA transport. Some proteins sty on the mana to facilitate translation.