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Matt's MCBG Exam 2 Study Guide > 8/15/14 - Protein Synthesis > Flashcards

8/15/14 - Protein Synthesis Flashcards

1
Q

What is the purpose of the 7-methylguanosine cap in translation initiation?

A

It binds the eIF cap-binding complex, which facilitates the recruitment of the small ribosomal subunit to the mRNA transcript.

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1
Q

What are the sizes of eukaryotic ribosomal subunits?

A

40S + 60S > 80S

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2
Q

What are the 3 stop codons?

A

UAA, UAG, UGA

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4
Q

What are 3 key features of the genetic code?

A
  1. It is redundant (there is more than 1 codon for each amino acid) 2. It is universal 3. Some codons have additional functions (start/stop codons)
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5
Q

List the 5 main steps of eukaryotic translation initiation

A
  1. Initiation tRNA bound to small ribosomal subunit 2. eIF4 complex binds to 5’ cap, 3’ tail 3. Ribosomal subunit recognizes 5’ cap and associated eiF4 complex, binds 4. tRNA scans for the first AUG using ATP as energy 5. GTP hydrolysis of eIF2 facilitates large ribosomal subunit binding, translation can now begin
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6
Q

What is the significance of the ester bond formed between an amino acid an tRNA?

A

It provides the energy for peptide bond formation during elongation.

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6
Q

What happens to EFTu-GTP if the codon/anticodon base pairing is incorrect?

A

If the base pairing is incorrect, GTP hydrolysis will be delayed, giving time for the tRNA to dissociate from the ribosome.

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7
Q

What are the main functions of the large and small ribosomal subunits?

A

Large: Catalyzes peptide bond formation Small: Provides framework to accurately match codon/anticodon

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7
Q

Why are eukaryotes monocistronic?

A

mRNAs usually require a 5’ cap to bind the ribosomal subunit. Since there is only 1 5’ cap per mRNA, there can only be one region where translation is initiated.

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9
Q

What is the difference between aminoacyl-tRNA synthetases in eukaryotes and prokaryotes?

A

Eukaryotes possess aminoacyl-tRNA synthetases specific to each amino acid. Prokaryotes possess aminoacyl-tRNA synthetases that recognize more than 1 amino acid.

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10
Q

What are the sizes of prokaryotic ribosomal subunits?

A

30S + 50S > 70S

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11
Q

What effect might a deletion/insertion have on protein synthesis?

A

Frameshift mutation

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12
Q

What are two ways aminoacyl-tRNA synthetase recognizes the correct tRNA?

A
  1. Anticodon recognition (does not work when multiple codons code the same amino acid) 2. Structural recognition at certain regions in the tRNA
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13
Q

Describe what occurs in A, P, and E sites during elongation?

A

A: tRNA enters and base pairs with mRNA P: Peptide bond is formed between amino acids at the A and P site. (also the initiation site) E: tRNA exit site

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14
Q

What are two ways aminoacyl-tRNA synthetase recognize the correct amino acid?

A
  1. Unique conformation of the binding site promotes correct binding of the amino acid (ex. a large amino acid won’t fit in a small binding site). 2. aminoacyl-tRNA synthetase pushes bound amino acid into editing site; if it fits, it is the incorrect amino acid
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15
Q

What is the main function of EFTu-GTP?

A

It binds loaded tRNA as it enters the ribosome to ensure the correct tRNA has been recruited.

16
Q

What are 4 differences between transcription and translation in prokaryotes?

A
  1. Transcription/translation can occur simultaneously 2. mRNAs are not processed with 5’ caps and polyA tails. 3. There is only 1 RNA polymerase 4. Ribosomal subunits are different sizes
17
Q

What is the main function of the Shine-Dalgarno box in prokaryotes?

A

SD box/16S rRNA base pairing determines the correct reading frame for translation.

17
Q

What are the two mechanisms by which tRNA is moved from A > P > E sites during elongation?

A
  1. Large ribosomal subunit translocates relative to the small subunit, placing the tRNAs in hybrid A/P, P/E sites. 2. EFG-GTP is hydrolized to induce a conformational change that pushes the tRNAs fully into the P and E sites.
19
Q

What are the major steps in protein synthesis?

A
  1. Loading (or charging) the tRNA with an amino acid 2. Initiation 3. Elongation 4. Termination
20
Q

What is the sequence for a start codon?

A

AUG

21
Q

What amino acid does a start codon encode?

A

Methionine

22
Q

List the 3 main steps of prokaryotic translation initiation

A
  1. Small ribosomal subunit binds at the SD box on the mRNA 2. tRNA/F-Met/IF2-GTP complex binds to the initiation site. 3. IF2-GTP is hydrolyzed to facilitate assembly of the large ribosomal subunit, initiation factors dissociate and translation can now begin
22
Q

How is eIF2-GDP catalyzed back into GTP form?

A

eIF2B (a guanine nucleotide exchange factor)

24
Q

Why are eukaryotes polycistronic?

A

The 5’ cap is insignificant in prokaryotes, since the ribosomes bind the mRNA through the activity of Shine-Dalgarno sequences. There can be multiple SD boxes on each mRNA, so more than 1 protein can be encoded.

25
Q

How would the inactivation of eIF2B alter protein synthesis?

A

eIF2B activates eIF2, which binds the large ribosomal subunit to the small subunit in order to begin translation. Inactivating eIF2B would stop protein synthesis at the initiation stage.

27
Q

What happens to EFTu-GTP is the codon/anticodon base pairing is correct?

A

GTP is hydrolized and EFTu-GDP dissociates from the tRNA, which allows the tRNA to fully move into the A site where translation can proceed. A 2nd delay following GTP hydrolysis offers 1 more opportunity for an incorrect tRNA to dissociate from the ribosome.

28
Q

What effect will a frameshift mutation have on protein synthesis?

A

The mRNA will be translated along the wrong reading frame.

29
Q

Describe the mechanism of action for Puromycin

A

It has similar structure to tyrosyl-tRNA, and can be incorporated into the growing polypeptide chain during elongation. However, further elongation is terminated due to its lack of a high energy bond.

30
Q

What effect will a nonsense mutation have on protein synthesis?

A

An early stop codon will result in a truncated protein.

31
Q

What is the main function of EFG?

A

It binds near the A site on the ribosome and accelerates the movement of tRNAs to the P and E sites.

32
Q

Describe the wobble phenomenon and how it relates to the redundancy of the genetic code

A

The 5’ base of the anticodon is not confined to a single nucleic acid for each amino acid. In other words, more than 1 nucleic acid at this position can code for the same amino acid.

33
Q

Which steps in protein synthesis is GTP hydrolysis thought to occur?

A

Initiation (EFTu/EFG) Elongation (eIF2)

34
Q

Draw the interaction between a messenger RNA codon and its cognate tRNA, labeling the orientations of both RNA strands.

A

Matt's MCBG Exam 2 Study Guide (13 decks)

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