Pre-mRNA processing LO

Question 1

What are the 3 major ways that mRNAs are processed?

Answer 1

1. capping
2. splicing
3. cleavage/polyadenylation

Question 2

what is capping?

Answer 2

addition of 7’methylGPPP cap to protect the exposed phosphate

Question 3

what is splicing?

Answer 3

removal of introns by excision

ligation of exons together to make complete readable sequence

Question 4

what is cleavage/polyadenylation?

Answer 4

removal of portion of 3’ end of by cleavage and then addition of polyadenosine tail to improve stability

Question 5

what is pre-mRNA?

Answer 5

the primary transcript from DNA, needs to be processed before it can be translated, does not have 5’ cap or poly A tail. contains introns

Question 6

what is mRNA in regards to pre-mRNA?

Answer 6

processed mRNA that is ready for translation into a protein

Question 7

what binds the 5’ cap to the pre-mRNA?

Answer 7

cap binding proteins (CBP)

Question 8

what is the functions of the 5’ cap?

Answer 8

1. promote splicing of proximal intron to cap
2. signal that mRNA is ready for export to cytoplasm
3. prevent degredation of mRNA

Question 9

what signals that mRNA is ready for degredation?

Answer 9

removal of the 5’ cap

Question 10

what is the function of eIF4E?

Answer 10

(eukaryotic initiation factor 4E)

promotes translation initiation

Question 11

what are the 3 steps required to place a 5’ cap to a pre-mRNA?

Answer 11

1. triphosphatase removes gamma phosphate from 5’ end
2. Guanylyltransferase adds GTP to terminal phosphate losing 2 phosphates from GTP in the process
3. 7 nitrogen of guanine methylated by methyl transferase

Question 12

what type of linkage is formed by guanylyltransferase?

Answer 12

5’ to 5’ linkage between phosphates of RNA and GTP

Question 13

what is the methyl donor in the methylation of 7 nitrogen of guanine?

Answer 13

S-adenosylmethionine

Question 14

what is the conserved consensus sequence in the 5’ end of an intron?

Answer 14

G U

Question 15

what is the conserved consensus sequence in the 3’ end on an intron?

Answer 15

A G

Question 16

what is the poly A site consensus sequence?

Answer 16

A A U A A A

Question 17

what is alternative splicing?

Answer 17

removal of different parts of a pre-mRNA to form different mRNA that will code for different proteins. Many pre-mRNA transcripts can code for multiple proteins but not until they are spliced at specific sites

Question 18

what are 2 diseases caused by splicing defects?

Answer 18

1. marfans syndrome

2. spinal muscular atrophy

Question 19

what is the presentation of Marfan’s syndrome?

Answer 19

very tall stature, long limbs, protruding sternum, weakness or defects of the aorta and heart valves

Question 20

what type of inherited disease is Marfan syndrome in regards to genetics?

Answer 20

dominant autosomal disease

Question 21

Marfan is a result of disruption of splicing of which gene transcript?

Answer 21

fibrilin

Question 22

what is fibrilin?

Answer 22

component of connective tissues

Question 23

mutations of the splicing of the fibrilin gene interfers with the binding of which molecules?

Answer 23

U1 and U2 with snRNAs which regulate splicing causing marfans

Question 24

what is the function of U1 snRNA in splicing?

Answer 24

recognized the 5’ splice sequence by base pairing with it (base pairs between the exon and the intron)

Question 25

what is the function of U2 snRNA?

Answer 25

recognizes the branch point between introns and exons

Question 26

what causes recognition of exons by the splicesome?

Answer 26

binding of U1 snRNA with U2 snRNA upstream of exons

Question 27

what is a branch point on a pre-mRNA?

Answer 27

series of nucleotides between exons

Question 28

what are the 2 reactions that make the mature 3' end of mRNA?

Answer 28

1. cleavage: 20 bp downstream of AAUAAA is cut by endonuclease exposing 3' hydroxyl group 2. at 3' OH, polyadenylation occurs

Question 29

what is the function of cleavage/polyadenylation specificity factor (CPSF)?

Answer 29

- associated with RNA pol II and polyadenylate polymerase - when poly A tail gets around 250 bp long, polyadenylate polymerase cannot bind to CPSF anymore and this signals termination of RNA pol II from transcribing

Question 30

What are the 3 major functions of an mRNA's poly A tail?

Answer 30

1. makes mRNA stable and prevents premature degredation 2. tail is bound by poly A binding protein (PAB I) which boosts translation in the cytoplasm by recruiting mRNA to ribosome 3. signals for transport from the nucleus to the cytoplasm

Question 31

how does alternative poly A sites cause more than one protein to be made from a single gene?

Answer 31

early termination of transcript by addition of the poly A tail can leave exons from being transcribed thus making a different protein

Question 32

what is an example of different poly A sites resulting in different proteins?

Answer 32

- IgM has 2 poly A sites | - MuS and MuM are 2 sites

Question 33

what type of IgM occurs from cleavage at the muS site?

Answer 33

antibody form that is secreted from plasma cells

Question 34

what type of IgM from cleavage at the muM site?

Answer 34

membrane bound antigen receptor on B cells