Lecture 38: Protein Synthesis I Flashcards

(29 cards)

1
Q

Components of protein synthesis process

A
  1. mRNA
  2. Ribosomes (organelle)
  3. tRNA (adaptor)
  4. Genetic code (language)
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2
Q

Features of genetic code in protein synthesis

A
  1. Degenerate (more than 1 codon for some AAs)
  2. Not ambiguous (no shared codons)
  3. Almost universal (besides mitochondria)
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3
Q

Mutation types

A
  1. Point
  2. Silent
  3. Missense
  4. Nonsense
  5. Insertion/deletion (frameshift)
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4
Q

Point mutation

A

Single base change

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5
Q

Silent mutation

A

Mutation results in same AA produced (codon degeneracy)

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6
Q

Missense mutation

A

Mutation results in different AA produced

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7
Q

Nonsense mutation

A

Mutation results in new stop codon

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8
Q

Insertion/deletion mutation (frameshift)

A

Adding or deleting 1 or more bases; frameshift if not multiple of 3

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9
Q

tRNA anti-codon/codon binding specificity and wobble

A

5’ and middle base in anti-codon/codon (tRNA/mRNA) interaction must bind perfectly
3’ base has wobble; flexible binding

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10
Q

Factor types needed for protein synthesis

A
  1. I (initiation)
  2. E (elongation)
  3. R (release)
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11
Q

AA activation steps

A

Both steps catalyzed by aminoacyl tRNA synthetase (specific kinds for given AAs)
1. AA + ATP → aminoacyl adenylate:synthetase + PPi
2. Aminoacyl adenylate:synthetase + tRNA → AA-tRNA + AMP + PPi

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12
Q

Role of AA activation for protein synthesis

A

Controls protein synthesis accuracy
1. Each synthetase has to recognize the AA and correct tRNA seq.
2. Each synthetase has activation site + hydrolytic site (error correction)
3. AA-tRNA that leaves cannot be corrected further

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13
Q

fMet

A

Formyl group added to Met w/ initiator tRNA to form fMet; all proteins start w/ fMet

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14
Q

Ribosome tRNA-AA sites

A
  1. A site (aminoacyl)
  2. P site (peptidyl)
  3. E site (exit)
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15
Q

Shine-Dalgarno sequence

A

At 5’ end of prokary. mRNA. Sets reading frame; 1st codon is always AUG (fMet) after Shine-Dalgarno.

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16
Q

Prokaryotic translation initiation process

A
  1. Shine-Dalgarno positions 30S subunit
  2. Initiator tRNA bound to fMet + IF2-GTP is positioned in P site
  3. 50S subunit binds; IF2-GDP + other IFs release
    Thus formation of 70S initiation complex
17
Q

Translation elongation cycle steps

A
  1. EF-Tu-GTP mediates binding codon specific AAcyl-tRNA to A site
  2. Peptide bond formation between growing peptide chain/tRNA in A site; mediated by peptidyl transferase ribozyme
  3. Free tRNA left in P site
  4. Ribosome translocation w/ EF-G-GTP opens new free A site for next tRNA
18
Q

Translation termination process

A
  1. Stop codon appears in A site
  2. RF1/2 bind A site
  3. RF3 binds common site
  4. Peptidyl transferase ribozyme catalyzes ester bond cleavage w/ GTP hydrolysis to release protein, tRNA, mRNA, ribosomal subunits
19
Q

Ribosome common site

A

EF-TU, EF-G, RF3 all bind same “common” site. This ensures 2 processes can’t occur simultaneously.

20
Q

Polyribosomes

A

Prokaryotic + eukaryotic feature where many ribosomes translate a gene simultaneously

21
Q

Protein synthesis inhibitors

A
  1. Tetracycline
  2. Chloramphenicol
  3. Puromycin
22
Q

Tetracycline

A

Blocks AAcyl-tRNA binding w/ A site in prokaryotes

23
Q

Chloramphenicol

A

Resembles peptide bond, inhibiting peptidyl transferase in prokaryotes

24
Q

Puromycin

A

Enters A site and accepts polypeptide chain, blocking translocation of ribosome in prokary. + eukaryotes.

25
Energy use for 100 AA peptide
- AA activation cleaves 2 high energy bonds - Initiation already places first tRNA in P site - Subsequent tRNAs need energy for A site binding + translocation (2 bonds) - Termination uses 1 bond
26
Hep C virus
Flavivirus; HCV virus + strand RNA use host ribosomes to synthesize viral protein. Does NOT insert into DNA
27
HIV
Inserts into genetic material and uses host genetic material to replicate
28
CF mutations
E.g. early stop codon (W1282X) causes premature stop
29