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39 Cards in this Set
- Front
- Back
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Several tRNA molecules joined together.
Function is filled in after name |
Multimeric tRNA precursor
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Need to trim off aditional nucleotides from the 3'-5' ends
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Monomeric tRNA precursor
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a. Cleavage/trimming
b. Nucleoside modifications c. CCA added to 3' end (nucleotidyl transferase) |
Modifications made to monomeric and multimeric precursors.
Need to trim molecules away from initial tRNA molecules. |
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The point of attachement to the mRNA molecule is through the adenylate molecule
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CCA
Added to the 3' end |
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1. Reductions
2. Deaminations 3. Rearrangements 4. Methylations |
Modifications made of tRNA.
Occur at the level of the polynucleotide |
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In prokaryotes, which RNA type is not extensively processed?
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mRNA
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In eukaryotes, is tRNA monomeric or multimeric?
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monomeric
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1. Synthesis of tRnA by RNA pol III
2. Trimming of nucleotides from both the 3' and 5' ends 3. Nucleoside modifications 4. Addition of the sequence CCA to the 3' end |
tRNA processing in eukaryotes
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1. Synthesis by RNA pol I (nucleolus)
2. Cleavage 3. Trimming 4. Methylation |
rRNA processing in eukaryotes
18S, 5.8S and 28S subunits |
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1. Addition of 5' cap
2. Addition of polyA tail to 3' end (polyadenylation) 3. Methylation of internal nucleoSides 4. RNA splicing |
mRNA processing in eukaryotes.
RNA pol II produces heterogenous RNA (hnRNA) |
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A mixture of precursor mRNA molecules
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heterogenous RNA (hnRNA)
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a. 7-Methylguanosine is joined to the 5' end of the mRNA in a 5'-triphosphate linkage.
b. Methyl groups are often found at the 2' position of the first and second nucleotides on RNA (DNA does not have a hydroxyl group) |
Properties of the 5' cap.
Thought to be crucial to splcing the mRNA Required for translation (protein synthesis) |
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The 5'-5' bond is not degraded by ____nucleases
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exonucleases
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1. Processing (splicing)
2. Stability 3. Transport from nucleus into cytoplasm 4. Translation |
Capping promotes mRNA
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1. Stability
a. Poly A binding protein binds to poly A tail. This is followed by other subunits binding to tail. - Prevents degradation of 3' end by exonucleases 2. Enhances translation |
Roles of poly(A) tail
According to dogma, histone mRNA's are the only mRNA's that lack a poly(A) tail |
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Methylation of internal nucleosides is a step in mRNA processing...
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however, it's function is unknown
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Informational nucleotide sequences
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Exons
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Non-informational nucleotide sequences
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Introns
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RNA splicing removes ______ and joins exons together
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introns
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Introns in a gene can be detected by hybridizing the mRNA with a ss-DNA fragment corresponding to the _______ strand of the gene
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nonsense strand (aka template strand/ noncoding strand)
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Distribution of introns in genes:
Histone genes and interferon genes have how many introns? |
None
Most genes for higher eukaryotes contain 1 to 10 introns |
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Distribution of introns in genes:
Collagen gene and dystrophin gene have what percentage of their gene coding for introns? |
Over 90% of the gene codes for introns
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5' splice site
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5'-GU
All introns begin with this sequence |
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3' splice site
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AG-3'
All introns end with this sequence |
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Branch point
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An adenylate residue.
Acts as a nucleophile. In order for splicing to occur, need all three splice points. |
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The 2' hydroxyl group of the
adenosine residue at the branch point acts as a nucleophile. •It attacks the phosphodiester bond at the 5' splice site. •Exon L1 is released. •”Lariat” structure is formed due to 2',5' phosphodiester bond involving guanosine and adenosine. •The adenosine residue is involved in three phosphodiester bonds. •The 3' end of exon L1 acts as a nucleophile attacking the phosphodiester bond at the 3' splice site. •The intron is released and then degraded. •Exons L1 and L2 are joined together. |
Concept: RNA splicing is a multistep process involving a series of nucleophilic attacks.
A unique structure formed in the process is the 'lariat' |
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Snurps (SnRNA):
U1 |
Binds 5' splice site
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Snurps (SnRNA):
U2 |
Binds the branch point
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Snurps (SnRNA):
U4 |
Regulation
When U4 binds to U6, blocks active site (noncompetitive inhibition) |
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Snurps (SnRNA):
U5 |
Binds 5' splice site
Displaces U1. |
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Snurps (SnRNA):
U6 |
Catalyzes splicing
Contains active site |
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Snurps (SnRNA):
Enzymatic complex is formed of which SnRNA? |
U4, U5 and U6
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Alternative splicing is required for producing extra genes
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Alternate processing of a primary transcript can generate different proteins from the same gene.
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Calcitonin (thyroid)
- Polypeptide (32 aa's) - participates in calcium and phosphate metabolism - increases deposition of calcium in bones Calcitonin gene-related peptide (brain) - polypeptide (37 aa's) - potent vasodilator - modulates acetylcholine receptor function at neuromuscular junction |
Alternative splicing can generate numerous isoforms from a single gene.
Each isoform may have different properties |
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Some functional protein, but not enough
Mutation on exon 1 gives rise to a different splice site -- Competes with the true splice site When the wrong splice site is used, loose portion of exon causes frameshift mutation Leads to termination of translation of exon 2 Will not form full protein |
alpha/beta + thalassemia
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No functional protein produced from the defective allele
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alpha/beta 0 thalassemia
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One or more defective alpha genes
Decrease in alpha-globin protein Decrease in Hb (a2b2) Free b subunits form a tetramer b4 is unstable leading to formation of Heinz bodies Hemolytic anemia |
alpha-thalassemia
Two copies of the alpha gene per chromosome (16) |
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One or more defective beta genes
Decrease in beta-globin protein Decrease in Hb (a2b2) Free alpha subunits Bind to and damage the RBC membrane Hemolytic anemia |
Beta-thalassemia
One copy of the B gene per chromosome (11) |
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Other mutations that can lead to thalassemia:
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1. Promoter site mutation
2. Mutations in signal for addition of poly(A) tail 3. Other mutations |
