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What are the three ways mRNA is modified?
- 5’ Cap
- Splicing (remember, occurs simultaneously with transcription)
- Addition of poly A tail (stabilizes mRNA and promotes transfer to cytoplasm
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What complex is responsible for modifying mRNA?
RNA pol II complex is responsible for capping, splicing, adding a poly A tail, and chromatin remodeling
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How do mRNA exit the nucleus?
They fold into a stem loop structure because of the cap and poly A tail and are able to exit the nucleus
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What signal results in the addition of a poly A tail?
AAUAAA sequence causes RNA to be cleaved (terminating transcription) on the 3’ end and an enzyme adds up to 200 A’s
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What mediates splicing?
snRNPs, which are part of the spliceosome
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What causes Spinal muscular atrophy?
Mutations in the survival of motor neuron protein (SMN), which disrupts the production of snRNPs
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What causes Lupus Erythematosus?
Antibodies to snRNPs
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What are the Spliceosomal snRNPs?
U1, U2, U4, U5, U6
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Describe the relationship between scaRNA, snRNP, and snRNA
For snRNPs to work (to aid in splicing), snRNA need to be modified with the help of scaRNA
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What is a disease caused by splice site mutations?
Beta-thalassemias
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How can 30,000 genes give rise to 100,000 proteins?
Alternative splicing – different proteins can arise from the same gene. The protein produced can be different depending on cell type, developmental stage, or even external environment
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What is a transition mutation?
Purine for a purine or pyrimadine for a pyrimadine
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What is a transversion mutation?
- Purine for a pyrimadine or pyrimadine for a purine
- What is a nonsense mutation?
- A codon that previously coded for an amino acid now codes for a stop codon
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What is a missense mutation?
A codon that coded for one amino acid now codes for another
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What is a Silent mutation?
Mutation does not change the desired amino acid
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What causes huntington’s disease?
Repeats of CAG sequence which codes for Q (also found in spinocerebellar atrophies)
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What causes S.C. ataxia I?
Repeats of CAG sequences which codes for Q (also found in huntinton’s disease)
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What causes fragile X syndrome?
More than 50 repeats of CGG in the 5’(before the gene) repetitive region of DNA. These repeats induce gene silencing via DNA methylation
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What causes myotonic dystrophy?
More than 30 CUG repeats in the 3’ (after the gene) repetitive region of DNA. These repeats reduce mRNA stability and induce heterochromatin
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What causes Friedreich’s ataxia?
More than 80 GAA repeats in intron 1. These repeats induce heterochromatin and decrease transcription
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