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EOM Test 2 > Protein Synthesis 1 > Flashcards

Protein Synthesis 1 Flashcards

1
Q

What are the three phases of translation?

A

Initiation

Elongation

Termination

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2
Q

What is the role of IF-1 and IF-3 in prokaryotic initiation?

A

Bind to the 30s (small) ribosomal subunit

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3
Q

What happens in prokaryotic initiation after the formation of IF-1/IF-3/30s complex?

A

IF-2GTP and N-formylmethionyl tRNA bind the complex and join to mRNA

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4
Q

What stimulates the binding of the 50s subunit?

A
  • Release of IF1 and IF3

- Hydrolysation of GTP to GDP and then release of IF2

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5
Q

What two processes happen simultaneously during eukaryotic translation initiation?

A

43s preinitiation complex formation

mRNA preparation

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6
Q

How is the 43s preinitiation complex formed?

A
  • eIF1,1A,and 3 bind the 40s ribosomal subunit

- methionyl-tRNA, eIF2-GTP, and eIF5 bind ribosome complex

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7
Q

What happens during mRNA preparation?

A
  • PABP binds the 3’ poly-A tail

- eIF-4F complex binds the 5’ end of the mRNA

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8
Q

What is the function of eIF4G?

A

Links the eIF4F complex to PABP

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9
Q

What is the function of eIF4E?

A

-binds the 5’ m7 G cap of mRNA

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10
Q

What is the function of eIF4B?

A

-unwinds secondary structures in the mRNA

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11
Q

What is the function of eIF3?

A

Binds both the mRNA and preinitiation complex, linking the two structures.

This new 48s initiation complex starts scanning.

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12
Q

What is the role of the kozak sequence?

A

Identifies the correct AUG start codon

usually the most 5’ AUG sequence

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13
Q

What is scanning?

A

The 48s initiation complex utilizes ATP in order to scan the mRNA for the start codon (AUG)

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14
Q

What occurs when the 48s initiation complex reaches the correct start codon?

A

eIF5 triggers eIF2GTP–>GDP, causing the eIFs to lose affinity for the complex and dissociate.

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15
Q

What is the role of eIF5B?

A

Has a bound GTP and recruits the 60s large ribosomal subunit to form the 80s ribosome via hydrolysis of GTP

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16
Q

Why are there two separate tRNAs that code for Met?

A

One for the initiation Met

One for internal Mets

17
Q

What are the 3 tRNA binding sites in ribosomes and their function?

A

A (aminoacyl or acceptor)- holds incoming tRNA

P (peptidyl) - carries growing polypeptide

E (exit) - empty tRNA exits

18
Q

What is the function of eEF1a-GTP?

A
  • Bring the charged tRNA to the ribosome
  • conformational change by the binding of the tRNA induces GTP hydrolysis, releasing eIF1a-GDP and leaving the tRNA in the A site.
19
Q

What is responsible for catalyzing the formation of new peptide bonds?

A

-Peptidyltransferase of the 60s ribosomal unit

20
Q

What is the function of eEF-2GTP?

A

mediates the translocation of the ribosome down the mRNA

21
Q

How does diptheria toxin work?

A

Inactivates eEF2, preventing elongation

22
Q

How does ricin work?

A

Cleaves adenine residue from the 60s subunit, resulting in the inability of eEF2 to bind

23
Q

What is the role of eEF1-By?

A

Exchanges GTP for bound GDP in eEF1a, recharging it and allowing it to bind to another tRNA

24
Q

What are the three stop codons?

A

UAA

UAG

UGA

25
Q

What is responsible for terminating protein synthesis?

A

Release factors

26
Q

What is the role of eRF-1?

A

Recognizes stop codons and binds eRF-3/GTP and enters A site

27
Q

What results from the binding of eRF1/eRF3 in the A site?

A

Polypeptide is released from the ribosome

Dissociation of the ribosomal subunits

28
Q

What are four ways of regulating protein translation?

A
  • Proteins that bind to either the 3’ or 5’ UTRs
  • Noncoding RNAs e.g. microRNAs and siRNAs
  • Phosphorylation
  • Modulation as a result of response to stress, nutrient availability, and growth factor stimulation
29
Q

How is the translation of ferritin regulated?

A

When iron is absent, iron regulatory protien binds to the iron response element in the 5’ UTR, blocking translation

30
Q

What is an example of translation regulation by binding of protein to the 3’ UTR?

A

Xlerk mRNA localization in Xenopus oocytes. 3’ binding proteins direct the mRNA to specific regions.

31
Q

How is eIF2 regulated by phosphorylation?

A

Phorphorylation of eIF-2 and eIF2B by regulatory protein kinases blocks the exchange of bound GDP for GTP.

32
Q

What is the role of 4E-BP?

A

Sequesters eIF-4E

When 4E-BP is phosphorylated it releases eIF4E so that the eIF-4F complex can form

33
Q

What are the roles of ATP and GTP during initiation?

A
  • ATP hydrolysis powers scanning
  • eIF-2 undergoes GTP hydrolysis to dissociate the pre-initiation complex
  • eIF-5B uses GTP hydrolysis to recruit the large subunit
34
Q

What are the roles of ATP and GTP during elongation?

A
  • Each tRNA used 1 ATP to charge the tRNA
  • eEF-1a uses GTP hydrolysis to bring a charged tRNA to the A site
  • eEF-2 uses GTP hydrolysis to power the translocation of the ribosome
35
Q

What is the function of streptomycin?

A

Inhibits initiation by binding to and distorting the structure of the 30s ribosomal unit

36
Q

What is the function of Tetracyclines?

A

Interacts with the 30s ribosome subunit to block access to the A site and inhibit elongation

37
Q

What is the function of Chloramphenicol?

A

Binds and inhibits the peptidyltransferase activity of the 50s ribosome, blocking elongation

38
Q

What is the function of erythromycin and clindamycin?

A

inhibit translocation of the ribosome by binding the 50s subunit, blocking elongation

39
Q

What is the function of Puromycin?

A

Enters the A site and is incorporated into the peptide, causing premature release of the polypeptide

Inhibits both prokaryotic and eukaryotic protein synthesis

EOM Test 2 (20 decks)

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