Rna Processing

Question 1

ribosomal rna

Answer 1

• rRNA
• bacterial and eukaryotic
• cytoplasm
  structural and functional components of the ribosome

Question 2

messenger rna

Answer 2

• mRNA
• bacterial and eukaryotic
• nucleus and cytoplasm
• carries genetic code for proteins

Question 3

transfer rna

Answer 3

• tRNA
• bacterial and eukaryotic
• cytoplasm
• helps incorporate amino acids into polypeptide chain

Question 4

small nuclear RNA

Answer 4

• snRNA
• eukaryotic
• nucleus
• processing of pre-mRNA

Question 5

small nucleolar RNA

Answer 5

-snoRNA
-eukaryotic
- nucleus
- processing and assembly of rRNA

Question 6

small cytoplasmic RNA

Answer 6

• scRNA
• eukaryotic
• cytoplasm
• variable

Question 7

MicroRNA

Answer 7

• miRNA
• eukaryotic
• cytoplasm
• inhibits translation of mRNA

Question 8

small interfering RNA

Answer 8

• siRNA
• eukaryotic
• cytoplasm
• triggers degradation of other RNA molecules

Question 9

RNA processing why

Answer 9

• after transcription, RNA has to be modified before it function
• it goes from being a primary transcript to mature RNA

Question 10

RNA processing: tRNA

Answer 10

• trimming at 5’ and 3’ ends, addition of nucleotides at 3’ end
• splicing of introns if present, by protein not snRNA spliceosomes)
• base modifications by specialized tRNA-modifying enzymes

Question 11

RNA processing: rRNA in prokaryotes

Answer 11

• extensive processing
• methylation of bases and 2’-OH or ribose
• cut and trimmed into smaller pieces (16S, 23S, 5s)
• often also contains sequences for tRNAs

Question 12

RNA processing: rRNA in eukaryotes

Answer 12

• primary 45S rRna transcript is exensively processed
  -extensive methylation of bases and 2’OH of ribose
• cut and trimmed into smaller pieces (28s, 18s, 5.8s)

Question 13

snoRNAs

Answer 13

• small nucleolar RNAs
• help cleave and modify eukaryotic rRNA and assemble them into mature ribosomes
• base pairs with the region where the modification will take place

Question 14

mRNA processing: eukaryotes

Answer 14

pre-mRNAs are modified in three ways
1. 5’ cap
2. splicing
3. cleavage at 3’ and adding polyA tail

• occurs in the nucleus
• mRNA is then exported out of the nucleus and translated by the ribosomes in the cytoplasm

Question 15

mRNAs can be further modified

Answer 15

• additional methylation of bases
• RNA editing (rare)

Question 16

5’ cap

Answer 16

• 7-methyl Guanosine attached to the 5’most nucleotide
• 2’OH of nucleotides 1 and 2 can be methylated but it’s not necessary

Question 17

Addition of 5’cap

Answer 17

• occurs soon after transcription starts
• phosphorylated CTD (of RNA polI) recruits capping enzymes
• above-mentioned recognizes the growing 5’ end
• gamma phosphate of residue 1 removed
• GTP is added in a 5’-5’ bond while releasing PPi
• guanine base of cap is methylated on N7
• possible further modifications

Question 18

3’ cleavage

Answer 18

• requires protein complex containing CPSF, CstF, cleavage factors (CFI, CFII), PolyA polymerase (PAP), polypeptides
• CPS binds to AAUAAA sequence, CstF binds to U-rich sequence -> loop formation
• mRNA I cleaved between the two sequences -> unknown mechanism
• 3’ sequences still attached to pol II and binding factors are released
• 3’ end is degraded and rna pol II gets signal to stop transcribing

Question 18

polyadenyltaion

Answer 18

• adding of polyA tail
• PolyA polymerase adds 10 As to the new 3’ end after 3’ cleavage
• PABII binds to polyA tail
• PABII stimutlstes PAP to add even more A
• whole polyA is Ultimatlely coveverd by PABII

Question 19

processing or mRNA without polA tail

Answer 19

• lack polyA tail but still get processed on the 3’ end
• have a hair pin before cleavage site and a consensus sequence downstream
• protein binds to hairpin and recruits U7 snRNP that interacts with consensus sequence and cleaves

Question 19

exons

Answer 19

parts of the genes that are transcribe and found in mature RNA
can be protein-coding or non-coding

Question 20

introns

Answer 20

sequences between exons that are transcribed but not found in mature RNA
mostly found in eukaryotic genes coding for mRNAs
are removed by splicing

Question 21

group I intron

Answer 21

• rRNA regions
• self-splicing

Question 22

group II intron

Answer 22

• protein-encoding genes in mito. and chloro
• self-splicing

Question 23

nuclear pre-mRNA

Answer 23

- protein-encoding genes in nucleus - spliceosomal

Question 24

tRNA

Answer 24

-tRNA genes - enzymatic

Question 25

what is needed for splicing (cis)

Answer 25

- 5' splice site: starts with GU -3' splice site: ends with AG - branch point A

Question 26

what is needed for splicing (trans)

Answer 26

- 5' splice site: starts with GU -3' splice site: ends with AG - branch point A plus - snRNPs - additional prtoens

Question 27

snrnps

Question 28

splicing principle

Answer 28

- pre mRNA splicing is catalysed by spliceosome - carried out in two transesterification reactions - results in fusion of two exons and release of intron