RNA molecules and processing

Question 1

3 primary regions of mature mRNA

Answer 1

-5’ untranslated region: binds to ribosomal complex, does not code for amino acids

-Protein coding regions

-3’ UTR: does not code for amino acids, affects mRNA stability and regulates its translation

Question 2

Post-transcriptional modifications to eukaryotic pre-mRNA

Answer 2

5’ cap: facilitates binding of ribosome to mRNA, one phosphate on 5’ end replaced with guanine, pairs with poly a tail

3’ cleavage and poly A tail: stabilizes mRNA, facilitates binding to mRNA + export out of nucleus

RNA splicing: removes introns

RNA editing: alters nucleotide, gRNA adds uridine monophosphate

Question 3

What is the splicing code for introns

Answer 3

1. 5’ splice sequence with GU
2. 3’ splice sequence with AG
3. Intron branch point with conserved “A”

Question 4

What is a spliceosome and its assembly details, and RNA splicing

Answer 4

An RNA/protein structure with 5 snRNAs that associate with 300 small proteins to form snRNPs (5 of them)

Assembly:

-snRNAs of spliceosome form base pairing with pre-mRNA
-U1 attaches to 5’ splice sequence
-U2 attaches to branch point
-U4,5,6 join spliceosome

Splicing:

1. pre-mrRNA cut at 5’ splice site and attaches to branch point
2. cut made at 3’ splice site and also the 3’ end of exon 1 is covalently attached to 5’ end of exon 2. lariat released and degraded

Question 6

Alternative RNA processing pathways

Answer 6

Alternative splicing

-pre-mRNA processed in different ways to produce alternative mRNA types
-alternative exons used

Multiple 3’ cleavage sites

-occurs in last exon
-generates longer or shorter exon
-may or may not produce different protein

Question 7

How is gene content changed by RNA editing

Answer 7

-endogenous guide RNAs direct insertion of uridine bases, causes new amino acids
-changing structures of individual bases

Question 8

tRNA modifications

Answer 8

-intron is spliced out
-extra 5’ and 3’ sequences removed
-bases 5’CAA 3’ added to 3’ end where amino acid will attach

Question 9

snRNAs

Answer 9

-act in complexes with proteins
-role in splicing

Question 10

snoRNAs

Answer 10

-act in complexes with proteins
-guides enzymatic chemical modifications of ribosomal RNAs within the nucleolus

Question 11

siRNA, miRNA

Answer 11

-double-stranded RNA
-regulate and controls gene expression

Question 12

CRISPR RNA

Answer 12

-functions as bacterial defense system
-works with Cas9 to cleave foreign DNA

Question 13

LncRNA

Answer 13

-regulate and controls gene expression at transcription or translation level by binding mRNA