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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
What complex is responsible for modifying mRNA?
RNA pol II complex is responsible for capping, splicing, adding a poly A tail, and chromatin remodeling
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
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
What mediates splicing?
snRNPs, which are part of the spliceosome
What causes Spinal muscular atrophy?
Mutations in the survival of motor neuron protein (SMN), which disrupts the production of snRNPs
What causes Lupus Erythematosus?
Antibodies to snRNPs
What are the Spliceosomal snRNPs?
U1, U2, U4, U5, U6
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
What is a disease caused by splice site mutations?
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
What is a transition mutation?
Purine for a purine or pyrimadine for a pyrimadine
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
What is a missense mutation?
A codon that coded for one amino acid now codes for another
What is a Silent mutation?
Mutation does not change the desired amino acid
What causes huntington’s disease?
Repeats of CAG sequence which codes for Q (also found in spinocerebellar atrophies)
What causes S.C. ataxia I?
Repeats of CAG sequences which codes for Q (also found in huntinton’s disease)
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
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
What causes Friedreich’s ataxia?
More than 80 GAA repeats in intron 1. These repeats induce heterochromatin and decrease transcription
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