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CMB2001 > CMB2001/L09 Post-transcriptional Control IIa > Flashcards

CMB2001/L09 Post-transcriptional Control IIa Flashcards

1
Q

What is the composition of a ribosome?

A

1/3 protein
2/3 mRNA

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2
Q

Describe tRNA charging (aminoacylation). (3)

A

Amino acid activation through nucleophilic attack (forming aa-AMP)
Formation of aminoacyl-tRNA (OH group of adenine 76 of tRNA attacks carbonyl carbon of aminoacyl-adenylate)
Forms aminoacyl-tRNA and AMP

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3
Q

Where in the ribosome do peptide bonds form?

A

P - peptidyl site
A - aminoacyl site

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4
Q

Give the 5 steps of translation elongation.

A

Aminoacyl-tRNA binding
Peptide bond formation
Translocation
GTP hydrolysis
Repeat

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5
Q

Give 2 features specific to eukaryotic mRNAs.

A

Cap
PolyA tail

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6
Q

Describe eukaryotic translation initiation. (5)

A

Small subunit binds CAP
Scans to first AUG for Met
Met-tRNA positioned
Large subunits joins
Transition to elongation

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7
Q

Why is mRNA circularised during initiation of translation?

A

Monitors integrity of mRNA
Brings ribosomes ending translation close to start site
Several other key translation factors

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8
Q

Give 3 proteins required for mRNA circularisation.

A

elF4E
G
PAB

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9
Q

What is the role of elF4E?

A

M7G binding

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10
Q

What is the role of elF4G?

A

Binds elF4E, a, 3, PABP

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11
Q

What is the role of elF4A?

A

ATPase
RNA helicase

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12
Q

What is the 43S pre-initiation complex?

A

Small subunits primed for associating with mRNA

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13
Q

What is the role of elF1A?

A

80S dissociation
Met-tRNA binding to 40S

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14
Q

What is the role of elF3?

A

80S dissociation
Binds many other elFs

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15
Q

What is the role of elF1?

A

AUG recognition

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16
Q

What is the role of elF2?

A

GTPase
Met-tRNA binding
Binds elF5

17
Q

What is the role of elF5?

A

Stimulates elF2 GTPase GAP for elF2

18
Q

What is needed for 43S association?

A

Interaction of elF3 and elF4G
RNA unwinding (elF4F unwinds cap-proximal sequence)

19
Q

What needs to occur to generate the ternary complex for further initiation events?

A

Recycling of elF2

20
Q

What is the role of elF5B?

A

GTPase
Promotes subunit joining

21
Q

Give a role of elF2B in the elF2 cycle.

A

Governs level of elF2-GTP (therefore initiation rate)

22
Q

Explain regulation of elF2B. (3)

A

Lower level than elF2
Down-regulated in response to stresses (viral infection, amino acid deprivation, ER stress)
Regulated through phosphorylation of elF2 (competitive inhibitor of elF2B)

23
Q

Describe the structure of elF2.

A

3 subunits (a, B, y)
a phosphorylated on Ser51 by PKR, PERK, GCN2, HRI
B binds elF2B, elF5
elF2y is a GTPase, binds Met-tRNA

24
Q

How is PKR activated?

A

By double stranded RNA (viral infection)

25
Q

What is PERK?

A

Mediator of unfolded protein response (ER stress)

26
Q

What is GCN2?

A

Regulator of translation in response to amino acid availability

27
Q

What is HRI?

A

Links globin availability to protein synthesis
Critical for RBC biogenesis

28
Q

What happens to elF2 kinases under stimulatory conditions?

A

Dimerise
Autophosphorylate and act on substrate

29
Q

Describe regulation of PKR.

A

Typically low expression
Increases when cells exposed to interferons (viral infection)
Binds dsRNA

30
Q

Describe iron response elements (IREs). Where are the found? What are they bound by?

A

Hairpin loops with conserved loop sequence
Bulge in stem
Found in 5’ or 3’ UTRs of iron-regulated mRNAs
Bound by IRP1&2

31
Q

Describe how low iron affects mRNA stability and translation.

A

IRP1&2 bind to IREs in mRNA
Inhibit translation by blocking ribosomal access or destabilising mRNA
Binding of IRPs protects from degradation

32
Q

Describe how high iron levels affect mRNA translation and stability.

A

Iron binds to IRP1 to reduce affinity for IREs, promoting ribosomal access and translation
Absence of bound IRP to mRNA promotes degradation

33
Q

Why is IRP1 described as a bifunctional protein?

A

With or without iron, has different functions
-Fe -> C-aconitase interconverts citrate and isocitrate
+Fe -> IRE1

CMB2001 (11 decks)

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