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CMB2001 > L09 > Flashcards

L09 Flashcards

1
Q

What type of ribosomes do prokaryotes have?

A

70S ribosome

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2
Q

What type of ribosomes do eukaryotes have?

A

80S ribosomes

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3
Q

What amount of ribosome is protein

A

1/3

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4
Q

What amount of ribosome is RNA

A

2/3

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5
Q

What does Ψ represent?

A

Pseudouridine

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6
Q

What is the most abundant posttranscriptionally modified nucleotide in cellular RNA?

A

Ψ

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7
Q

What enzyme modifies uradine -> Ψ?

A

Ψ Synthases

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8
Q

What enzyme carries out the charging of tRNA?

A

Aminoacyl-tRNA synthetases

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9
Q

How many steps are there in the reaction that results in tRNA charging?

A

2

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10
Q

What is the first step in tRNA charging?

A

Amino acid activation

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11
Q

What type of mechanism occurs when the amino acid and ATP bond?

A

Nucleophilic attack

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12
Q

What is the second step in tRNA charging?

A

OH group of adenosine 76 of tRNA attacks the carbonyl carbon of the adenylate = aminoacyl-tRNA and AMP

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13
Q

What type of reaction is a peptide bond formation?

A

Dehydration-condensation reaction

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14
Q

What is the A site?

A

Aminoacylated tRNA binding site

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15
Q

What is the P site?

A

Polypeptide chain site

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16
Q

What is the E site?

A

Exit site

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17
Q

Which part of the ribosome is the exit tunnel located?

A

Large subunit

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18
Q

What does elongation factor 2 (G) do?

A

causes movement of ribosome along the mRNA, making the A site available

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19
Q

How is the register reset?

A

The amino acid on P shifts to E and leaves the ribosome, resetting the register?

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20
Q

What does the ribosome catalyse?

A

Peptide bond formation

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21
Q

Is the catalysis of the ribosome an RNA-catalysed event - true or false?

A

True

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22
Q

What does tRNA deliver?

A

Amino acids

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23
Q

Where is the expanding polypeptide chain attached to?

A

P-site tRNA

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24
Q

How many A’s do poly(A) tails normally have?

A

250 A

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25
What protein is poly(A) bound by?
Poly(A) binding protein
26
What happens in the absence of PAB's (Poly(A) binding protein)
They're exposed to nucleases and get turned over quickly AND they are inefficiently translated
27
Where does the small ribosome unit initially bind?
Cap (5'cap)
28
What is the Kozak consensus
CC(A/G)CCAUG
29
What does Kozak consensus do?
Promotes recognition of AUG
30
Why is the RNA circularised?
Brings together the factors that binds the mRNA that all promote translation initiation and monitors the integrity of the RNA
31
What does eIF4E bind to?
m7G (5') cap
32
What does eIF4G bind to?
eIF4E, eIF4A, eIF3, PABP (scaffolding protein)
33
What does el4A bind to?
ATPase, RNA helicase
34
What does the elF4F complex contain?
eIF4E, eIF4A, eIF4G
35
What does elF3 bring?
Small ribosome subunits
36
What proteins are required for circularisation?
eIF4E, G and PAB.
37
What is the ternary complex made of?
Met, eIF2 and GTP
38
What are the components of the 43s pre-initiation complex?
Small subunit, eIF1,1A,2,3,5, GTP and Met
39
Describe the 43s pre-initiation complex
Small subunit primed for associating with mRNA
40
What is needed for 43s associations?
Interactions between eIF3 and eIF4G RNA unwinding, eIF4F (4A - helicase) unwinds cap proximal sequence.
41
What is the eIF4F composed of?
eIF4E, eIF4G, eIF4A
42
What is scanning?
Movement of small subunit down RNA to AUG
43
What happens once AUG is recognised?
Hydrolysis of GTP -> GDP+Pi, released with eIF2, as well as the release of other eIF
44
What are the components of the elongation cycle?
aa-tRNA entry , codon recognition and proof reading, peptide bond formation, translocation
45
When is the ribosome reset?
After the peptide bond is formed
46
What happens when the termination codon is reached?
Translation stops and the ribosome dissociates
47
Enlist a summary of key events in eukaryotic translation
eIF4A complex binds cap & interacts with PAB to circularise the mRNA. Small subunit binds to the cap, scans mRNA until AUG is located Large subunit joins Translocation is required to move tRNA and mRNA through the ribosome Termination codon = translation stops & ribosome dissociates
48
When does most of translation regulation take place?
Initiation
49
What are the key regulation points in mRNA translation?
Formation of the eIF4F complex - if these are not bound, then SSU does not bind to mRNA Prevent 43s complex from binding. Ternary complex formation/recycling of eIF2B (exchange factor)
50
Compare the levels of eIF2 and eIF2B present normally
eIF2B < eIF2
51
What does eIF2B activity govern?
eIF2B activity governs level of active eIF2-GTP and thus overall initiation rate
52
In response to what is eIF2B activity down-regulated?
eIF2B activity is down-regulated in response to stresses such as viral infection, amino-acid deprivation, endoplasmic reticulum stress
53
How is eIF2B regulated?
regulation is through phosphorylation of eIF2, which becomes a competitive inhibitor of eIF2B
54
What are the consequences of regulatory methods?
consequence: generation of ternary complex is impaired, translation initiation of mRNA is reduced
55
How many subunits does eIF2 have?
3
56
What does eIF2alpha do?
Phosphorylated on Ser51 by PKR, PERK, GCN2, HRI - responding to stresses.
57
What does eIF2beta do?
Binds eIF2B, eIF5
58
What does eIF2gamma do?
GTPase, Met-tRNA
59
Since eIF2 > eIF2B, a small amount of eIF2 phosphorylation can decrease ternary complex levels substantially
60
eIF2 Kinases and what do they respond to?
PKR - activated by double stranded RNA (viral infection) PERK - a mediator of the unfolded protein response (endoplasmic reticulum stress) GCN2 - a regulator of translation in response to amino acid availability “general amino acid control of gene expression, non-derepressing” HRI - linking globin availability to protein synthesis - critical for red blood cell biogenesis
61
How do eIF2 kinsases function?
Dimerise, and then act on substrate.
62
Outline the mechanism of how PKR operates in response to a viral infection?
PKR expression is typically LOW increases when cells are exposed to INTERFERONS Interferons - produced & released by (animal) cells infected by VIRUSES dsRNA binding…… reproduction of many (RNA) viruses generates dsRNA when PKR binds dsRNA it dimerises and is activated
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CMB2001 (9 decks)

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