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Genetics > Lecture 17 > Flashcards

Lecture 17 Flashcards

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Biology 101 flashcards
1
Q

Eukaryotic Translation overview

A

Methionine is first amino acid (isn’t formulated)

  • Special kind of initiator tRNA that binds AUG
  • No shine dalgarno on mRNA - 7-methylG cap assists in binding of ribosome
  • Preferred start codon sequence - RXXAUGG
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2
Q

What is start codon sequence

A

RXXAUGG

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3
Q

What does 7-methylguanine cap and PolyA tail do?

A

Stabilise mRNA

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4
Q

Number of eukaryotic initiation factors?

A

12

eIF1A, eIF1B, eIF2A etc

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5
Q

Step 1 of Initiation in eukaryotic translation

A

mRNA bound by eIF4 family

eIF4E recognises cap

eIF4G acts as scaffold between cap and polyA - forms closed loop complex

Small subunit bound by initiator tRNA and several initiation factors - recruited via eIF4G/eIF3 interaction

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6
Q

Step 2 of initiation in eukaryotic translation

A

Pre-initiation complex scans for start codon

eIF4A/4B complex has ATP-dependent helicase activity - drawing mRNA through till start codon located

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6
Q

Step 3 of initiation in eukaryotic translation

A

Start codon identified

GTPase activity of eIF2 activated

conformational shift

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7
Q

Step 4 of initiation in eukaryotic translation

A

Large subunit binds

Majority of eIFs released

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7
Q

Eukaryotic elongation

A

eEF1A = EFTu - binds aminoacyl tRNA and GTP

eEF1B - EFTs - GTP exchanged for GDP

eEF2 = EFG - involved in ribosome translocation

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8
Q

Termination

A

Similar to prokaryotes

eRF1 binds stop codon whilst attached to eRF3-GTP

eRF3-GTP is hydrolysed to eRF3-GDP, releasing Pi

eRF3-GDP replaced by ABCE1-ATP, removing polypeptide

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9
Q

What does fusidic acid do?

A

Inhibits elongation at EG mediated translocation step

  • Binds EFG-GDP - prevents release from ribosome

Blocks A site for next aa incorporation

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10
Q

What does fusidic acid target?

A

Primarily staphylococci

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11
Q

What does puromycin do?

A

Mimics aminoacyl-tRNA due to aromatic amino acid linked to base

Treated by ribosome as incoming aminoacyl-tRNA

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12
Q

Diphtheria toxin

A

63kDa polypeptide formed by Corynebacterium diphtheriae

Catalyses ADP-ribosylation of eEF-2

Blocks eukaryotic protein synthesis

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13
Q

Ricin

A

Lectin protein

Very toxic by inhalation, injection or ingestion

LD50 is 5-10 micrograms/kg via inhalation or injection

30-40mg/kg orally

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14
Q

Explain ricin as a type 2 ribosome inactivating protein (RIP)

A
  • Prepro-polypeptide with A and B chain

Split by proteolysis - still linked by disulphide cysteine-cysteine bridge

Chain B - lectin glycoprotein - binds galactose - enters cell via membrane/ER

Chain A - RNA N-glycosidase - depurinates adenine on 28S rRNA - adenine sandwiched between 2 tyrosine rings - then hydrolysed

Genetics (18 decks)

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