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MFoM > Translation & Regulation of Translation > Flashcards

Translation & Regulation of Translation Flashcards

1
Q

Prokaryotic ribosome subunits

A

50S subunit: 23S +5S rrNA 30S subunit: 16SrRNA Total: 70S ribosome

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2
Q

Eukaryotic ribosome subunits

A

60S subunit: 28S + 5.8 S + 5S rRNA 40S subunit: 18SrRNA Total: 80S ribosome

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3
Q

degenerate (genetic code)

A

more than 1 codon for some aa’s

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4
Q

non-ambiguous (genetic code)

A

1 codon can only specify 1 aa

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5
Q

silent mutation

A

a change that specifies the same amino acid

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6
Q

missense mutation

A

a change that specifies the same amino acid

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7
Q

nonsense mutation

A

a change that produces a stop codon

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8
Q

insertion/deletion

A

addition or deletion of one or more bases; if 1 or 2 bases only–> will cause a frameshift

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9
Q

wobble

A
  • base pairing between codon/anticodon in 5’ and middle codon bases must be perfect
  • some flexibility in 3’ base of codon *allows mRNA to be translated with fewer than 64 tRNAs
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10
Q

tRNAs

A

adaptor molecules with bind both amino acids and mRNA codons

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11
Q

aminoacyl tRNA synthetases

A

protein synthesis requires energy amino acids are activated with ATP prior to tRNA attachment (this enzyme carries out both steps) synthetase is specific for a given amino acid

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12
Q

prokaryotic initiation

A
  • Shine-Dalgarno sequence positions 30S subunit so initiator tRNA is in P site
  • Shine-Dalgarno base-pairs with 3’ end of 16S rRNA -formyl-met is first aa incorporated
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13
Q

prokaryotic elongation

A
  • aa-tRNA -EF-Tu-GTP enters the A site, start of the cycle (also the rate-limiting step)
  • EF-Tu-GDP is recycled (with EF-Ts) (correct positioning involves the TYC loop, which is complementary to the sequence in 5S RNA)
  • Formation of peptide bond with transfer of growing peptide chain to the tRNA in the A site, leaving free tRNA in P site (catalyzed by peptidyl transferase; ribozyme component of 23SrRNA)
  • Translocation from P–>E mediated by elongation factor EF-G-GTP (requires energy, hydrolyzed)
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14
Q

prokaryotic termination

A
  1. Stop codon (UAA, UAG, UGA appears in A site)
  2. RFe-GTP binds ribosome
  3. Hydrolysis of GTP
  4. Cleavage of ester bond (peptidyl transferase)
  5. Release of protein, tRNA, mRNA, ribosomal subunits
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15
Q

tetracycline

A

inhibitor of protein synthesis; blocks binding of aminoacyl-tRNA to A-site of ribosome (prokaryotes only)

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16
Q

chloramphenicol

A

resembles peptide bond; inhibits peptidyl transferase activity (prokaryotes only)

17
Q

puromycin

A
  • looks like a tRNA
  • enters A site and accepts polypeptide chain; translocation is blocked (prokaryotes and eukaryotes)
18
Q

differences between prokaryotic and eukaryotic initiation

A
  • capped mRNA -initiation factors (eIF)
  • no fmet tRNA (met-tRNA initiator or i)
  • locate Kozak sequence (which includes AUG start codon in it, almost always first AUG after cap)
  • small subunit binds at cap
19
Q

eukaryotic initiation steps

A

how much to include?

20
Q

HCV IRES

A
  • recognized specifically by the small ribosomal subunit / eukaryotic initiation factor (eIF3)
  • interactions allow cap-indepedent initiation of viral protein synthesis through + scaffold eIFG
21
Q

regulation of eukaryotic translation (EIF2B)

A
  • EIF2-GTP–> binds the initiator tRNA and forms a complex with the 40S r subunit
  • Under stress: (oxidative, temperature), nutrient deprivation, lack of heme (reticulocytes), double-stranded RNA (induces production of interferon) etc, which stimulates production of eIF2B (kinase), eIF2 has 100X more affinity to it
  • eIF2B phosphorylates it EIF2-GDP, inhibiting protein synthesis
22
Q

RNA interference / post transcriptional gene regulation in lower eukaryotes

A

dsDNA–(Dicer; RNAse III-like enzyme)–>

siRNAs (2 unpaired nucleotides at 3’ ends–>

RISC (RNA-induced silencing complex, contains an endonuclease activity)–>

activated RISC–> (antisense strand remains associated with RISC) target mRNA–>

Argonaute (slicer) is the enzyme within RISC responsible for mRNA degradation

23
Q

microRNAs

A
  • Naturally occurring silencing RNAs in mammalian cells synthesized as longer hairpin precursors in the nucleus by Pol II
  • Processed by Drosha to form pre-miRNA in nucleus (transported to cytoplasm and processed by Dicer; RISC retains antisense strand)
  • RISC bind to mRNA 3’ untranslated regions (imperfect pairing) and inhibit translation
  • May also lead to mRNA degradation (perfect pairing)

MFoM (6 decks)

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