T.16 DNA MATURATION AND TRANSPORT

Question 1

When does RNA maturation take place?

Answer 1

At the same time as transcription.

Question 2

What is the state of RNA when it is released from RNA pol II?

Answer 2

It is almost mature due to simultaneous processing.

Question 3

What does the primary transcript contain?

Answer 3

Introns and exons.

Question 4

Where does RNA maturation occur?

Answer 4

Inside the nucleus.

Question 5

What happens if maturation fails?

Answer 5

RNA cannot pass to the cytoplasm.

Question 6

What are the main processes involved in RNA maturation?

Answer 6

Capping, RNA splicing, excision, and polyadenylation.

Question 7

What is an additional rare modification RNA can undergo?

Answer 7

RNA editing.

Question 8

What are the aims of RNA maturation?

Answer 8

RNA protection and codifying region selection.

Question 9

How is RNA protected during maturation?

Answer 9

Strand ends are modified to prevent exonuclease recognition.

Question 10

What is the role of splicing in region selection?

Answer 10

It removes introns that do not contain coding information.

Question 11

What domain regulates RNA maturation?

Answer 11

The CTD domain of RNA polymerase II.

Question 12

When does capping begin?

Answer 12

Immediately after RNA transcription starts.

Question 13

What does the 5’ end of RNA initially contain?

Answer 13

A triphosphate group.

Question 14

What enzyme acts first in capping?

Answer 14

Phosphohydrolase.

Question 15

What does phosphohydrolase do?

Answer 15

Removes the gamma phosphate from the 5’ end.

Question 16

What enzyme associates with RNA pol II during capping?

Answer 16

Guanilyltransferase.

Question 17

What does guanilyltransferase do?

Answer 17

Adds a guanine to the 5’ end of the RNA.

Question 18

What follows the guanine addition during capping?

Answer 18

Guanine-7-methyltransferase methylates the guanine.

Question 19

What bond is formed after capping?

Answer 19

A triphosphate bond with RNA.

Question 20

What additional enzyme can enhance RNA cap stability?

Answer 20

2’-O-methyltransferase.

Question 21

What complex binds the RNA cap for protection?

Answer 21

CBC (Capping Binding Complex).

Question 22

What are the stages of polyadenylation?

Answer 22

Slow polyadenylation and rapid polyadenylation.

Question 23

What are the function of polyadenylation?

Answer 23

1. Protect the 3 end
2. End transcription

Question 24

What happens during slow polyadenylation?

Answer 24

The 3’ side is prepared for poly(A) tail addition.

Question 25

What does CPSF do?

Answer 25

Recognizes the polyadenylation signal and cleaves the strand.

Question 26

What is the role of CStF?

Answer 26

Assists CPSF in recognizing and cutting the RNA.

Question 27

What is the function of cleavage factor (Cf)?

Answer 27

Works with CPSF and CStF to cut the 3’ end.

Question 28

What happens during rapid polyadenylation?

Answer 28

PAP adds the adenine chain to the 3’ end.

Question 29

What does PAPB II do?

Answer 29

Controls tail length and helps transport mRNA to the cytoplasm.

Question 30

When does PAPB II inactivate PAP?

Answer 30

When the poly(A) tail is large enough.

Question 31

What happens to the poly(A) tail during translation?

Answer 31

It is degraded by nucleases.

Question 32

What happens to mRNA after multiple translations?

Answer 32

It is degraded.

Question 33

When does splicing occur?

Answer 33

During transcription.

Question 34

What triggers splicing during transcription?

Answer 34

Proteins bound to RNA pol II.

Question 35

What is removed and what is retained during splicing?

Answer 35

Introns are removed; exons are retained.

Question 36

What are the intron sequence features?

Answer 36

Start with GU, end with AG.

Question 37

Where is the branch point located?

Answer 37

25–50 bases upstream from the AG end.

Question 38

What helps regulate the splicing process?

Answer 38

Ribonucleoproteins attached to intron sequences.

Question 39

What is the first step in the molecular splicing mechanism?

Answer 39

Oxygen of the branch point attacks phosphate of exon 1.

Question 40

What is the second step in the splicing mechanism?

Answer 40

Nucleophilic attack joins exon 1 and 2 by phosphodiester bond.

Question 41

What is alternative maturation?

Answer 41

Alternative polyadenylation or splicing to produce different proteins.

Question 42

What is alternative splicing?

Answer 42

Some introns are not removed, or splice sites vary, creating different mRNAs.

Question 43

What does alternative splicing promote?

Answer 43

Genetic diversity.

Question 44

What regulates alternative splicing?

Answer 44

ESE, ESS, ISE, ISS.

Question 45

What does an exonic splicing enhancer (ESE) do?

Answer 45

Binds proteins to enhance exon recognition.

Question 46

What does an exonic splicing silencer (ESS) do?

Answer 46

Binds proteins to inhibit exon recognition.

Question 47

What do intronic splicing enhancers and silencers (ISE/ISS) do?

Answer 47

Enhance or inhibit intron recognition respectively.

Question 48

What is alternative polyadenylation?

Answer 48

mRNA is cleaved at different polyadenylation sites post-transcription.

Question 49

What is the result of alternative polyadenylation?

Answer 49

Two different proteins are produced from the same transcript.

Question 50

What is mRNA editing?

Answer 50

Sequence changes in RNA like substitutions or deletions.

Question 51

Where does mRNA editing occur?

Answer 51

In very few genes.

Question 52

What is an example of RNA editing?

Answer 52

ApoB mRNA edited in intestine from CAA to UAA (stop codon).

Question 53

What is the effect of ApoB RNA editing?

Answer 53

Shorter protein in the intestine compared to the liver.

Question 54

What happens after RNA transcription and maturation?

Answer 54

mRNA is surrounded by transport proteins forming mRNP.

Question 55

What is mRNP?

Answer 55

messenger ribonucleoprotein complex for nuclear export.

Question 56

What structure regulates mRNA transport across the nuclear membrane?

Answer 56

Nuclear pore complex.

Question 57

What direction does mRNA travel through the pore?

Answer 57

From 5’ to 3’.

Question 58

What happens to ribonucleotides during export?

Answer 58

They are retained in the nucleus.

Question 59

How can mRNA be transported in other cells?

Answer 59

In exosomes via endocytosis or membrane fusion.