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Translation Flashcards

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1
Q

What is translation?

A

The process of synthesizing proteins from an mRNA template.

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2
Q

In which direction is mRNA read during translation?

A

5′ to 3′.

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3
Q

In which direction is a polypeptide synthesized?

A

From the N-terminus to the C-terminus.

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4
Q

What is a codon?

A

A triplet of nucleotides on mRNA that encodes a specific amino acid.

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5
Q

What are the three stop codons?

A

UAA, UAG, and UGA.

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6
Q

What is the start codon in most organisms?

A

AUG, which codes for methionine.

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7
Q

What is the Shine-Dalgarno sequence?

A

A ribosome-binding site in prokaryotic mRNA upstream of the start codon.

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8
Q

What is the function of tRNA?

A

To deliver specific amino acids to the ribosome by matching its anticodon to mRNA codons.

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9
Q

What enzyme charges tRNA with its corresponding amino acid?

A

Aminoacyl-tRNA synthetase.

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10
Q

How many different aminoacyl-tRNA synthetases exist?

A

At least one per amino acid; approximately 20.

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11
Q

What is the energy source used in tRNA charging?

A

ATP.

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12
Q

What ensures high fidelity in translation?

A

Proofreading by aminoacyl-tRNA synthetases and accurate codon-anticodon pairing.

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13
Q

What is wobble base pairing?

A

Flexibility in the third position of the codon that allows non-standard base pairing.

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14
Q

Which base in the anticodon often allows wobble pairing?

A

Inosine.

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15
Q

What are the three ribosomal sites for tRNA binding?

A

A (aminoacyl), P (peptidyl), and E (exit) sites.

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16
Q

What catalyzes peptide bond formation in the ribosome?

A

The peptidyl transferase activity of rRNA in the large ribosomal subunit.

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17
Q

What is the role of EF-Tu in elongation?

A

It brings aminoacyl-tRNA to the A site using GTP.

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18
Q

What is the role of EF-G?

A

It promotes translocation of the ribosome after peptide bond formation.

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19
Q

What is the function of IF-3 in prokaryotes?

A

Prevents premature association of 50S subunit with 30S during initiation.

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20
Q

What is the role of IF-2?

A

It delivers the initiator fMet-tRNA to the P site.

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21
Q

What is the function of IF-1?

A

It blocks the A site to ensure correct positioning of the initiator tRNA.

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22
Q

What distinguishes tRNA^fMet from other tRNAs?

A

It carries N-formylmethionine and is used only for initiation in prokaryotes.

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23
Q

What happens after the initiation complex is assembled?

A

The 50S subunit joins, GTP is hydrolyzed, and elongation begins.

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24
Q

How is the initiation process different in eukaryotes?

A

It involves scanning for the start codon and requires the 5′ cap for ribosome recruitment.

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25
What eIF recognizes the 5′ cap in eukaryotic mRNAs?
eIF4.
26
Which eukaryotic initiation factor brings Met-tRNA to the P site?
eIF2-GTP.
27
What happens to eIFs after initiation?
They are released as the large ribosomal subunit joins.
28
What is the role of eIF5?
It facilitates GTP hydrolysis and assembly of the 80S ribosome.
29
What is the final step of elongation?
Translocation of the ribosome to the next codon.
30
Which site does the next aminoacyl-tRNA enter?
The A site.
31
What terminates translation?
Recognition of stop codons by release factors.
32
What is the function of RF-1 and RF-2 in prokaryotes?
They recognize stop codons and promote release of the polypeptide.
33
What is the role of RF-3?
It promotes GTP-dependent release of RF-1 and RF-2.
34
What happens after the polypeptide is released?
The ribosome disassembles and mRNA is released.
35
What are chaperones?
Proteins that assist in folding newly synthesized polypeptides.
36
What is the function of Hsp70?
It binds nascent polypeptides to prevent misfolding.
37
What are chaperonins?
Protein complexes that provide a folding chamber for proper protein folding.
38
What is the function of protein disulfide isomerase (PDI)?
It catalyzes disulfide bond formation and rearrangement.
39
What is the function of prolyl isomerases?
They catalyze cis-trans isomerization of proline residues.
40
What are signal peptides?
Short N-terminal sequences that direct proteins to specific cellular locations.
41
What happens to the signal peptide after translocation?
It is typically cleaved by signal peptidases.
42
Where is translation initiated in eukaryotic cells?
In the cytoplasm, often on free or ER-bound ribosomes.
43
How are ribosomes targeted to the ER?
Via the signal recognition particle (SRP) that binds the signal peptide.
44
What are the subunits of prokaryotic ribosomes?
30S (small) and 50S (large) subunits.
45
What are the subunits of eukaryotic ribosomes?
40S (small) and 60S (large) subunits.
46
What is the complete ribosome in prokaryotes?
70S ribosome (30S + 50S).
47
What is the complete ribosome in eukaryotes?
80S ribosome (40S + 60S).
48
What links amino acids during translation?
Peptide bonds catalyzed by the ribosome.
49
Which component of the ribosome is catalytic?
rRNA in the large subunit.
50
How many high-energy bonds are consumed per peptide bond?
At least four: two for amino acid activation, one for elongation, one for translocation.
51
What is an open reading frame (ORF)?
A continuous stretch of codons without stop codons that encodes a polypeptide.
52
What is the function of the 5′ untranslated region (UTR)?
Regulates translation initiation and ribosome binding.
53
What is the function of the 3′ UTR?
Influences mRNA stability and translational efficiency.
54
What causes polysomes to form?
Multiple ribosomes translating a single mRNA simultaneously.
55
What is a polyribosome?
A complex of one mRNA and multiple ribosomes translating it.
56
What role does GTP play in translation?
It provides energy for tRNA delivery, ribosome movement, and termination.
57
What happens if the reading frame shifts?
It results in a completely different and likely nonfunctional protein.
58
What is the role of the cap-binding complex in eukaryotic translation?
It recruits the ribosome to the 5′ end of the mRNA.
59
What does 'degenerate code' mean?
Multiple codons can encode the same amino acid.
60
What ensures the correct reading frame is chosen in eukaryotes?
The ribosome scans from the 5′ cap to the first AUG in a favorable context.
61
What are the minimum requirements for translation?
mRNA, ribosomes, charged tRNAs, initiation/elongation/termination factors, and energy (ATP/GTP).
62
How is translation terminated?
When a stop codon is reached and recognized by release factors.
63
What is the function of elongation factors?
They facilitate tRNA entry and ribosome movement during elongation.
64
What ensures translation starts at the correct AUG?
In prokaryotes: Shine-Dalgarno sequence; in eukaryotes: Kozak consensus sequence around AUG.
65
What does 'degenerate code' mean?
It means multiple codons can encode the same amino acid, adding redundancy to the genetic code.
66
What does 'unambiguous code' mean?
Each codon specifies only one amino acid.
67
Why is translation considered energy-intensive?
Because it consumes large amounts of ATP and GTP for amino acid activation, initiation, elongation, and translocation.
68
What is the function of the signal recognition particle (SRP)?
It binds signal peptides and directs ribosomes to the ER membrane for co-translational translocation.
69
What are release factors and what do they do?
Proteins that recognize stop codons and promote hydrolysis of the polypeptide from the tRNA.
70
How does translation differ between prokaryotes and eukaryotes in terms of initiation?
Prokaryotes use the Shine-Dalgarno sequence; eukaryotes use 5′ cap recognition and scanning for AUG.
71
What is the role of the Kozak sequence in eukaryotes?
It enhances recognition of the start codon by the ribosome.
72
How do antibiotics like tetracycline and erythromycin affect translation?
They inhibit specific steps of bacterial translation, often by targeting ribosomal subunits.
73
What happens during the scanning process in eukaryotic initiation?
The 40S ribosomal subunit scans the mRNA from the 5′ end to find the start codon.
74
What defines the reading frame in translation?
The position of the start codon (AUG) determines the triplet grouping of nucleotides.
75
What is the importance of maintaining the reading frame?
Frameshifts alter the entire amino acid sequence downstream, often leading to nonfunctional proteins.
76
What is translational coupling?
In prokaryotes, the translation of one ORF can affect the translation of another in a polycistronic mRNA.
77
How do post-translational modifications affect protein function?
They regulate protein activity, localization, stability, and interactions.
78
What are common post-translational modifications?
Phosphorylation, glycosylation, acetylation, methylation, ubiquitination, and disulfide bond formation.
79
What is the first step in protein folding?
Formation of secondary structures such as α-helices and β-sheets guided by the primary sequence.

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