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MHG 1 > Translation > Flashcards

Translation Flashcards

1
Q

History of genetic code

(6)

A
  1. Zamecnik: radioactive AA → found radioactive proteins
  2. Zamecnik & Hoagland: activate a tRNA by incubating w/ liver extracts (couple AA onto tRNA)
  3. Francis Crick: reasoned RNA could “translate” genetic code to AA sequence of protein
  4. Nirenberg: 1st to crack code. Made RNA monomers and added to extracts to synthesize monomer polypeptides
  5. Nirenberg & Leder: triplet binding studies
  6. Khorana: made synthetic RNA dimer, trimer, tetramers

*triplet non-overlapping code; three reading frames *64 codons for 20 AA (3stop codons) = degenerate code

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2
Q

Wobble hypothesis

(3)

A

wobble position: 5’ anticodon / 3’ codon

  1. C and A only recognize one codon
  2. U and G can recognize two codons (G:U pairing)
  3. I can recognize three codons (AUC)
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3
Q

tRNA activation

A

Catalyzed by aminoacyl-tRNA synthetase

  1. AMP is coupled to AA + PPi released
  2. AA is transferred to 3’OH of tRNA at C terminal

*32 tRNAs

*certain ribonucleotides on tRNA (including anticodon) are important in synthetase recognition

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4
Q

tRNA proofreading

A

Mistakes occur about 1/10,000 AA

Hydrolytic site on tRNA removes wrong AA

  1. Val & Thr
    - Val (-CH3) is preferred in acylation site
    - Thr (-OH) is preferred in hydrolytic site
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5
Q

Charcot-Marie-Tooth disease

CMT

A

Heterogenous inherited disorder of nerves (neuropathy)

Loss of muscle tissue and touch, predominantly feed and legs

  1. Mutation in glycyl-tRNA synthetase: CMT2D
    * axonal polyneuropathies
  2. Mutation in tyrosyl-tRNA synthetase: intermed CMT
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6
Q

Diamond Blackfan anemia (DBA)

A
  1. Mutations in RPS19 & RPS24 (ribosomal protein small subunit); required for maturation of 40S subunits and for binding of eIF2
  2. Abormal thumb, short, dys heart, kidney, glaucoma
  3. Impairment of mRNA translation initiation if both mutated. Decrease in ribosomal levels if RPS19 mutated
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7
Q

Prokarytotes Initiation

A
  1. mRNA binds to ribosomal small subunit & guided to correct position by pairing of Shine-Dalgarno sequence in 5’ end of mRNA; upstream of start codon; helps lock in
  2. transformylase adds N-formyl group to tRNAfMet → fMet-tRNAfMet
  3. then Binds to IF-2-GTP → binds to P site of small 30S ribosome
    * anticodon (CAU) pairs with initiator codon (AUG)

*IF3 stops the 50S subunit from attaching too soon

*IF1 blocks A site to prevent premature binding of tRNAs

  1. large 50S subunit attaches to form initiation complex →GTP hydrolysis
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8
Q

Eukaryotes Initiation

A
  1. mRNA 5’ cap binds to 40S small ribosomal subunit
  2. Met-tRNAiMet binds to subunit with eIF2-GTP

*eIF4F helps scan mRNA for AUG

  1. Large 60S subunit joins → GTP hydrolysis & eIF2-GDP released
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9
Q

Vanishing White Matter (VWM)

A

1, Mutation in eIF2B, which regenerates eIF2-GTP during eukaryotic translation initiation

  1. Ataxia with CNS hypomyelination
  2. Deregulation- increase unfolded protein response, slows synthesis; doesn’t activate as well
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10
Q

Wolcott-Rallison (WRS)

A
  1. Mutation in PERK (impair or abolish fxn)
  2. PERK (ER kinase) phosphorylates eIF2 and inhibits it
  3. Leads to insulin overproduction→ cells overload w/ unfolded insulin → death of ß cells of pancreas → diabetes mellitus I
  4. Dysfxn kidney, liver, pancreas, mental retardation, central hypothyroidism
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11
Q

Prokaryotes Elongation

A
  1. 23S rRNA ribozyme catalyzes peptide bond formation within large 50S subunit
    * Nucleophilic attack of carbonyl carbon by amino nitrogen of incoming AA
  2. EFG binds to A site with hydrolysis of GTP and transloccation of ribosome
  3. Uncharged tRNA is released from E site

*GTP is recycled back with TS

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12
Q

Eukaryotes Elongation

A
  1. 28S rRNA ribozyme catalyzes peptide bond formation in large 60S subunit
  2. eEF2 binds to A site with hydrolysis of GTP and translocation of ribosome
  3. Uncharged tRNA is released from P site

*GTP is recycled back with TS

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13
Q

Prokaryotes & Eukaryotes Termination

stop codons: UAA, UAG, UGA

A
  1. Either RF1 or RF2 bind to A site (1 = UAA UAG, 2 = UAA UGA) eukaryotes only RF1
  2. Peptide is hydrolyzed from last tRNA
  3. RF3 helps in disocciation from ribosome, occurs with ATP hydrolysis
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14
Q

Gastric Cancer

A
  1. Mutations in eRF3 predispose to gastric cancer -20 fold
  2. GGC expansion

Mutation in termination of translation

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15
Q

Initiation inhibitors

A

PROKARYOTES ONLY

  1. Streptomycin: changes shape of rRNA and causes misread of mRNA
  2. Neomycin: bends RNA causing misreading or blocking initiation
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16
Q

Elongation inhibitors

A

Block pepidyl transferase

  1. Cycloheximide (EUKARYOTES)
  2. Chloramphenicol (PROKARYOTES & mito): binds rRNA and inhibits formation of peptide bond

Alters rRNA (depurinates)

  1. Ricin (EUKARYOTES)

_Act at A site _

  1. Tetracyclin (PROKARYOTES): interferes with tRNA anticodon reading of mRNA codon
  2. Erythromycin (PROKARYOTES): binds to rRNA and prevents movement
  3. Fusidic acid (PROKARYOTES)
  4. Diptheria toxin (EUKARYOTES)

Stops translocation

  1. ADP-ribosylates EF2 (EUKARYOTES)
17
Q

Termination inhibitors

A

Premature chain termination

  1. Puromycin- mimics 3’ end of AA-tRNA

*Macrolide inhibitors are being tested to cause misreading of certain genetic mutations to “correct” tranlation

MHG 1 (10 decks)

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