Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

cmb2001 > lecture 9 > Flashcards

lecture 9 Flashcards

1
Q

What is a ribosome made up of?

A

~1/3 protein
~2/3 RNA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

How do tRNA bind?

A

Anticodon binds to codon
3’ end, CC end

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What reaction does aminoacyl-tRNA synthetases catalyse?

A

1) Amino acid activation - amino acid and ATP bind catalytic site, nucleophilic attack by α-carboxylic acid oxygen yielding aminoacyl-adenylate (aa-AMP)
2) Hydroxyl group of adenine 76 of tRNA attacks the carbonyl carbon of the adenylate, forming aminoacyl-tRNA and AMP

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

How is a peptide bond formed between aminoacylated tRNA and polypeptide?

A

Takes place on polypeptide chain site of ribosome
The aminoacylated tRNA binding site before the polypeptide chain site
The exit site after the polypeptide chain site to allow mRNA to leave ribosome

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Are tRNAs present on the aminoacylated tRNA binding site and polypeptide chain site?

A

Yes
eg: the expanding polypeptide chain is attached the the P-site tRNA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How does translation elongation occur?

A

mRNA moves along three bases to introduce new tRNA to ribosome initiated by elongation factor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is peptide bond formation catalysed by?

A

the ribosome

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What does eukaryotic translation initiation depend on?

A

The 5’ cap on the mRNA
Small subunit binds the cap, moves (scans) to the first AUG, encoding the initiating methionine of the protein

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the Kozak consensus sequence?

A

5’-ACCAUGG-3’
The most frequently found sequence around the AUG in eukaryotic mRNA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Why is mRNA circularised during translation initiation?

A

Monitors integrity of mRNA
Brings ribosomes ending translation close to the start site
Brings proteins ending translation close to the cap
Key translation factors bind to it also

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are the proteins needed for mRNA circularisation?

A

elF4E, G, PAB

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the 43S pre-initiation complex?

A

Small subunit primed for associating with mRNA
Preparing small subunit (40S) for translation
EIF3 multifactorial
Prevent 40S from binding to 60S to keep in cytoplasm for translation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is needed for 43S association?

A

Interactions - elF3 with elF4G
RNA unwinding: most 5’ UTRs has at least some structure - elF4F (4A) unwinds cap-proximal sequence

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the 48S pre-initiation complex?

A

Small subunit associated with the AUG codon
5’ proximal AUG is used unless very close to cap
Consensus GCC(A/G)CCAUGG inserted before natural AUG meaning new AUG is used
Mutation of initiator tRNA anticodon (to 3’-UCC-5’) results in use of complementary codon (AGG)
Requires elF4F

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are the main parts of elongation translation?

A

-elF4F complex binds cap
-Small subunit recruited to the cap
-then scans along until it finds the start AUG
-large subunit joins
-Translocation to move the tRNAs and mRNA through the ribosome
-reach termination codon, translations stops and the ribosome dissociates

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are the key regulation points of translation?

A

Formation of elF4F
43S Binding
Function of elF2B/ Ternary complex formation

17
Q

How is elF2 regulated?

A

Activated by elF2B
Multiple protein kinases phosphorylate a single serine
This inhibits the GEF activity of eIF2B

18
Q

What is elF2Bs function ?

A

Regulates protein synthesis
It reactivates the G protein eIF2, which, in its GTP-bound form, binds initiator methionyl-tRNA (Met-tRNAMeti) to form GTP-eIF2 ternary complex (TC)
The TC is delivered to the 40S small ribosomal subunit before mRNA binding

19
Q

How is elF2B different to elF2?

A

elF2B is present at a much lower level
elF2B activity governs level of active elF2-GTP and thus overall initiation rate

20
Q

How is elF2B regulated?

A

Through phosphorylation of elF2, which becomes a competitive inhibitor of elF2B

21
Q

What is a consequences of elF2 acting as a competitive inhibitor for elF2B?

A

generation of ternary complex is impaired, translation initiation of mRNA is reduced

22
Q

What cause elF2B to be down-regulated?

A

In response to stresses, such a viral infection, amino-acid deprivation, endoplasmic reticulum stress

23
Q

What proteins regulate the elF2 cycle?

A

elF2α - phosphorylated on Ser51 by PKR, PERK, GCN2, HRI
elF2β - binds elF2B, elF5
elF2γ - GTPase, Met-tRNA

24
Q

What is the key regulatory step in the elF2 cycle?

A

Since elF2 > elF2B, a small amount of elF2 phosphorylation can decrease ternary complex levels substantially

25
Q

What are the elF2 kinases?

A

PKR, PERK, GCN2, HRI

26
Q

What is PKR activated by?

A

double stranded RNA (viral infection)

27
Q

What is PERK a mediator of?

A

the unfolded protein response (endoplasmic reticulum stress)

28
Q

What is GCN2 a regulator of?

A

translation in response to amino acid availability “general amino acid control of gene expression, non-derepressing”

29
Q

What is the role of HRI?

A

linking globin availability to protein synthesis - critical for red blood cell biogenesis

30
Q

What do all elF2 kinases have in common?

A

they are all stresses
they dimerise under stimulatory conditions
they autophosphorylate and act on substrate (elF2 Ser51)

31
Q

How does PKR use an antiviral defense strategy?

A

PKR expression is typically low but increases when cells are exposed to interferons
dsRNA binding - reproduction of many virus
When PKR binds dsRNA it dimerises and is activated

32
Q

How is iron metabolism regulated?

A

levels of FE in the cell regulate the expression of FE storage/transport proteins
Fe found in heme and iron-sulphur clusters

33
Q

What regions in mRNAS regulate translation?

A

UTRs - untranslated regions

34
Q

What are iron response elements?

A

Hairpin loops with a conserved loop sequence and a bulge within the stem
Found in the 5’ or 3’ UTRs of iron-regulated mRNAS
Bound by iron regulatory proteins - IRP1 and IRP2

35
Q

How do iron levels affect mRNA translation and stability?

A

Low iron: translational repression and mRNA stabilisation
High iron: translational activation and mRNA degradation

36
Q

What type of protein is IRP1?

A

Bifunctional
Binding of IRP1 to mRNA can block or activate translation
IRP1 binding can also affect mRNA stability

cmb2001 (10 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions