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BMS-I > Translation > Flashcards

Translation Flashcards

1
Q

Is translation a reversible process?

A

Generally, no

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2
Q

Why is it said that the genetic code is mostly degenerate?

A

AA have many RNA codons coding for them. Not readily reversible

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3
Q

What is the difference between nonsense, silent, and missense mutations?

A

Nonsense: pt. mut changes codon from AA to a termination seq.

Silent: pt mut. But doesnt change codon recognition

Missense: pt mut. Changes one AA to another

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4
Q

What is between the 5’ cap and the start codon?

A

5’UTR

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5
Q

What is the universal start codon?

A

AUG - M/Met/Methionine

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6
Q

What are the stop codons for protein translation?

A

UGA
UAA
UAG

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7
Q

Where is the poly(A) tail added? How many nucleotides is it composed of?

A

In the nucleus, about 200

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8
Q

If a base is deleted from the genetic code, what type of translational error will result?

A

Frameshift

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9
Q

What type of RNAs read protein code?

A

TRNAs

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10
Q

At what end of tRNAs is the AA attached to?

A

3’

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11
Q

What is the purpose of the anticodon loop?

A

Codon recognition

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12
Q

What enzymes recognize tRNAs and add the appropriate amino acid? IS this an ATP required step?

A

Aminoacyl tRNA synthetases

ATP required

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13
Q

How many types of aminoacyl tRNA synthetases are there?

A

20.

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14
Q

How many active sites do AAtRNAS have? What are their purposes?

A

2

One for synthesizing and one for editing

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15
Q

How do we classify ribosomes?

A

Ribozyme - peptide formation without contribution of a protein.

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16
Q

What is the 80S eukaryotic ribosome composed of?

A

60S and 40S

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17
Q

What are the three tRNA binding sites on ribosomes?

A

A (aminoacyl site) -> initial tRNA binding

P (peptidyl site -> peptide binding site

E (exit) -> tRNA release

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18
Q

What are the three phases of mRNA translation?

A
  1. Initiation
  2. Elongation
  3. Termination.

(You can have multiple ribosomes on a single RNA molecule)

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19
Q

What tRNA molecule does the 40S subunit bind with to produce a pre-intiation complex?

A

Initiator tRNA.

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20
Q

What is the initiator tRNA usually associated with?

A

Binds methionine and eIF2

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21
Q

What is eIF2 usually associated with?

A

GTP. GTP hydrolysis acts as a switch to start up sequence.

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22
Q

What does eIF4E associate with?

A

5’ cap of mRNA

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23
Q

What does eIF4g associate with?

A

/eIF4E creates a sort of scaffolding complex

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24
Q

What is the only step that requires ATP during mRNA translation?

A

When the initiator moves along mRNA it requires helicase activity to keep going looking for an AUG. This requires ATP

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25
Q

What is step 2 of the initiation sequence of translation?

A

Scanning mRNA for AUG codon

26
Q

What is step 3 of initiation sequence of translation?

A

Large subunit joining

27
Q

What happens when large ribosomal subunit binds?

A

GTP hydrolysis to GDP and eIF2 and other initiation factors dissociate.

28
Q

What is the first step of elongation in protein translation?

A

Delivery of aa-tRNA to A site and E site release.

Aa-tRNA delivered with eEF1A bound with GTP.

29
Q

How does aatRNA bind to A site?

A

EEF1A associated with GTP guide molecule and GTP hydrolysis binds it to A site while kicking of eEF1A

30
Q

What is second step of elongation in protein translation?

A

GTP hydrolysis and eEF1A release

31
Q

What happens if the wrong aatRNA is delivered?

A

Preferentially dissociate.

32
Q

What is eEF2’s role in protein translation?

A

Catalyzes translocation. Signals to ribosome to move on to next codon

33
Q

What is the 3rd step of elongation in translation?

A

EEF2 binding to catalyze translocation

34
Q

What is the 4th step of translational elongation?

A

GTP that was bound with eEF2 gets hydrolyzed and dissociates. Opens the A site back up.

35
Q

At what step in translational elongation does the E site release?

A

1st step. With aa-tRNA delivery via eEF1A and GTP

36
Q

What tRNAs does eEF1A not bind to?

A

Initiator tRNA + selecocysteine tRNA

Binds all others

37
Q

Are there any terminating tRNAs? How does protein translation terminate?

A

No.

Protein -> eRF1 (releasing factor)

Bacteria have 2 of these RF.

Comes in at stop codons:

  1. UAG
  2. UGA
  3. UAA
38
Q

Does bacterial mRNA have a 5’ cap?

A

No, they are polycistronic and translation happening immediately after transcription.

39
Q

What initiates bacterial translation?

A

Shin-Dalgarno sequence (upstream of codon); directly BP with ribosomal RNA.

40
Q

Compare and contrast Eukaryotic and Prokaryotic translational methods:

A

Eukaryotic: Prokaryotic

  1. Monocistronic mRNA. Polycistronic
  2. 40S+60S->80S ribosome. 30+50->70S
  3. EIF4e (5’ cap bound). No counter
  4. EIF2 (binds initiator tRNA w/gtp). IF2
  5. EIF4G (Binds to eIF4E, scaffold) No counter
  6. EEF1A (deliver AAtRNA, kicks out E). EFTu
  7. EEF2 (translocation (frees up A site). EFG
41
Q

How is translation post-transcriptionally regulated?

A
  1. RNA editing (rare)
  2. MiRNAs
  3. Iron storage
  4. Poor nutrition
  5. Hypoxia
42
Q

What is an example of mRNA editing?

A

MRNA editing happens post-transcription, but pre-translational.

ApoB is made in liver and intestine.

Intestine needs a shorter form of the protein.
ApoB mRNA is edited to produce a premature stop codon (via a nonsense mutation)

43
Q

What are miRNAs?

A

Short RNA molecules that BP w/ mRNAs and regulate translation (typically during development)

44
Q

How do miRNAs inhibit translation?

A

BP with 3’UTR region and create RISC complexes thought to physically impede translation

45
Q

What diz are correlated with miRNA function?

A
  1. Cancers (breast,lung)
  2. Viral diz (HCV, HIV)
  3. Immune related diz
  4. Neurodegenative diz
46
Q

How is iron homeostasis regulated?

A

Iron sensing protein (IRP)

47
Q

What is the iron regulatory element? How does it work in regards to iron levels?

A

Stem-loop sequence of mRNA structure.

Iron regulatory protein binds with there is no iron ->prohibiting translation

If there is iron present, IRP cannot bind with stem-loop IRE and translation proceeds.

Gene is on ferritin mRNA

48
Q

When there is a shortage of nutritional AA, what happens to protein syn?

A

Down regulated

49
Q

How does eIF2 become phosphyraled?

A
  1. [aa] decreased
  2. Cellular stress
  3. Immune response
  4. Unfolded proteins
50
Q

Why are guanine exchange factors (GEF) important?

A

After GTP gets hydrolyzed to GDP, need something to exchange it. Back.

GEFs req. b/c affinity for GDP is much higher than that GTP

51
Q

What is the GEN for eIF2?

A

EIF2B

52
Q

What happens when eIF2 gets phosphorylated during stressful events?

A

This phosporylated eIF2 sequesters eIF2b and forms an inactive complex

53
Q

What does mTOR stand for? What does it do?

A

MTOR- mammalian target of rapamycin.

Signaling pathway that represses translation in response to hypoxia thru eIF4E regulation.

Cellular rheostat. (Upregs in growth, down in stress)

54
Q

In normoxia and growth, how does mTOR regulate eIF4E?

A

It does not directly regulate on top of eIF4E. Instead presence of mTOR phosphorylates 4EBP-1 which prevents them from binding to eIF4E

55
Q

What happens when hypoxic cell conditions are introduced into the cell (in terms of mTOR)>?

A

Less mTOR is produced, which reduces 4EBP-1 inactivation. Allows 4EBP-1 to bind with eIF4E and inhibit translation.

56
Q

What is the 21st AA? How is it produced?

A

Selenocysteine (essential)

Enzymatically converted from serine.

Incorporates via modified UGA (stop) codon

57
Q

What enzymes that use selenocysteine are required for thyroid hormone synthesis?

A

Deiodinases

58
Q

What is the elongation factor that recognizes Sec-tRNA?

What is the tRNA that recognizes special UGA codons?

What is the SECIS element?

What is Secis BP 2 (SBP2)?

A
  1. EEFSec
  2. Sec-tRNA sec
  3. 3’ UTR rna seq. Required for sec incorporation
  4. Binds secis region and helps recruit to get sec in at the specialized stop codon
59
Q

When can a single mRNA encode for more than one protein?

A

Prokaryotes

Also is ribosome is frameshifting

60
Q

How does a ribosome frame shift?

A
  1. Slippery site

2. Pseudoknots.

61
Q

How does the diptheria toxin work?

A

Modifies elongation factor responsible for translocation (eEF2). (3rd step of elongation)

BMS-I (17 decks)

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