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22 Cards in this Set
- Front
- Back
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What is the different between mRNA splicing in prokaryotes and eukaryotes?
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Pro:
- sequences of the gene the RNA and the protein are colinearly organized and expressed. Euk: - nucleus contains hnRNAs - much larger size than mRNA - short half-lives |
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Both hnRNA and mRNA contain....
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Caps and tails
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Describe R-loop hybridization
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- Partial denaturation of DNA plus addition of complimentary RNA
- dsDNA: RNA hybrids form R-loop structures - DNA:RNA hybrids > stability than DNA: DNA hybrids - R-loops can be visualized by electron microscopy |
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___ are removed and ____ are spliced together
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Introns
Exons |
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What is the variety of intron sizes and numbers?
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- Size 50 - > 10,000 nucleotides
-#/gene: 0 - > 50 - ( can make up 99% of the gene sequence) - Can have small gene and huge gene and small gene codes for more (big gene has more introns) |
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What are genes without introns?
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- Heat shock proteins
- Interferons - Histones |
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What do introns do?
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1. Contribute to the evolution of protein families
2. Multiple introns increase protein-coding potential |
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Exons encode the function ____ of proteins
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Domains
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____ and _______ produces new proteins
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Gene duplication, exon shuffling
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TRUE or FALSE: recombination more likely to occur in small introns than in large exons?
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False: recombinations more likely to occur in large introns than in small exons.
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Alternative splicing
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The same gene can produce different proteins.
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TRUE or FALSE: Splicing mechanism must be precise to prevent frameshifts or premature termination that would produce non-functional proteins.
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TRUE.
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_______ nucleotide sequences at splice junctions
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Consensus
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What are splicing mechanisms?
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1. Endonucleolytic cleavage and ligation
- enzyme mediated - precise 2. Autocatalytic splicing - mediated by the RNA 3. Spliceosome-mediated - 2 step reaction carried out by spliceosomes |
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What is endonucleolytic cleavage and ligation?
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An enzymatic reaction requiring endonuclease and ligase activity.
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What is autocatalytic splicing?
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- Intron removed without involvement of protein catalytic activity
- Splicing activity is intrinsic to the RNA "catalytic RNA" -Mechanism occurs in may lower eukaryotes - No external energy source required - Each intron excised by 2 phosphodiester bond transfers - 2 degree structure of the RNA brings reactive groups together for catalysis |
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How does autcatalytic splicing occur?
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Reaction requires free 3'-OH of a guanine nucleotide.
G 3'-OH attacks 5'-P of intron 3'-OH of exon attacks 5'-P of exon 2 - exons joined. Intron circularizes by internal phosphodiester bond transfer and is rapidly degraded. |
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What is spliceosome-mediated splicing?
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- Mechanism used to splice out introns in pre-mRNAs in the nucleus
1. snRNP U1 binds 5' splice site, U2 binds branch site and U5 binds 3' splice site 2a. spliceosome assembly 2b. 5' site cleavage: exon 1/GU-intron 3.a formation of intramolecular phosphodiester linkage between 5' carbon of G at cleavage site of 2' crbon of A residue at branch 2 3b. U1 and U4 released 4. 3' splice site cleavage and the two exons joined by 5'-3' phosphodiester bond |
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What are spliceosomes?
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Ribonucleoprotein complexes composed:
- 5 types of dnRNAs: U1-U6 - 40 different proteins together forming snRNPs |
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There are _____ different amino acids
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20
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R groups can be...
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1. Hydrophobic
2. Hydrophilic 3. Acidic 4. Basic |
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eh
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weg
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