RNA processing

Question 1

RNA processing modifications made to mRNA

Answer 1

• add 5’cap (before transcription is finished)
• add polyA tail
• RNA splicing

Question 2

What does a P body do

Answer 2

• gets rid of RNA in the cytoplasm that is no longer required
• de capping enzyme removes 5’cap
• deadenylase removes polyA tail
• cytoplasmic exosome degrades

Question 3

What is alternative splicing

Answer 3

• yields different mRNAs from the same gene in different cells or at different developmental stages
• increases protein diversity without increasing the genome

Question 4

Sex determination is drosophila

Answer 4

Sxl, Tra and Dsx regulate sexual differentiation
1. Sxl controls its own splicing, STOP codon in exon 3
males: 2, 3, 4 - no Sxl protein
females: 2, 4 - Sxl protein produced
2. Tra splicing is regulated by Six, STOP codon in exon 2
males: 1, 2, 3 - no Tra protein
females: 1, 3 - Tra protein produced
3. Dsx splicing is regulated by Tra to get sex isoforms
males: 3, 5 - whole gene = 12356-An
females: 3, 4-An - whole gene = 1234-An

Question 5

What is the role of alternative splicing in the preception of sounds

Question 6

What are miRNA

Answer 6

small RNA molecules that regulate stability and translation of mRNAs
- bind IMPERFECTLY to target mRNA
- binding is usually within the 3’-UTR
- imperfect binding leads to repression of translation

Question 7

What are siRNA

Answer 7

small RNA molecules that regulate stability and translation of mRNAs
- bind PERFECTLY to the target RNA and cause its rapid degradation by RNA interference
- degrade viral RNA and RNA produced by transposons

Question 8

how is miRNA generated (biogenesis)

Answer 8

4 proteins facilitate…
1. Drosha removes 5’ and 3’ end in ds RNA
2. exportin transports the processed miRNA to the cytoplasm
3. dicer cuts the ds RNA into small pieces, chops off hairpin loop
4. Argonaut (in RISC) removes one of the strands of dsRNA

Question 9

What is RNA interference (in the cytoplasm)

Answer 9

1. dsRNA is cleaved to small RNA fragments by an endonuclease called DICER
2. small dsRNAs bind to RISC and form an inactive complex
3. argonaut in RISC is a helicase and unwinds dsRNA to form active RISC*
4. RISC* is guided by single-stranded siRNA (full complementarity) of miRNA (partial complimentarity) and cleaves or inhibits the target mRNA (SLICER activity of argonaut)`