Translation Flashcards

1
Q

mRNA role

A

carries codon

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2
Q

tRNA role

A

adaptors between codon + aa

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3
Q

rRNA role

A

associates with a set of proteins to form ribosomes

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4
Q

RNA polymerase characteristics

A

RNA polymerase synthesises RNA in a 5’-3’ direction
• RNA polymerase does not need a primer.
• The RNA product does not remain base-paired to the
template DNA strand

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5
Q

Polycistronic transcripts

A

mRNA which encodes two or more proteins.

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6
Q

Role of aminoacyl tRNA sythetase

A

Loading -> high fidelity

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7
Q

Initiation in bacteria

A

RNAP recognises starting AUG by shine-dalgarno motif 6-8 nt upstream AUG

  • > pairs with polypyrimidine motif in small ribosome sub-unit rRNA
  • > position AUG in P site
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8
Q

Initiation in eukaryotes

A

5’ to 3’ scanning for Kozak sequence which contains AUG

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9
Q

Elongation general mech:

A

Ribosome places aa-tRNA in A site facilitated by GTPase elongation factor

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10
Q

GTPase elongation factor in bacteria v eukaryotes

A

EFTu (bacteria)/ eEFIA (eukaryotes)

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11
Q

What happens in the initial selection phase?

A

aatRNA in complex with EFtu is rejected/accepted by ribosome

  • > if accepted GTP hyrolysed
  • > EFTu leaves ribosome - proofreading will reject wrong tRNA
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12
Q

What happens after selection?

A

Peptide bond formation in large sub-unit

-> growing polypeptide chain from P site to nucleophilic amine of A site

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13
Q

How are tRNA’s translocated to the Exit site?

A

GTPase couples GTP hydrolyses to translocate tRNA to E site

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14
Q

How do the GTPases used for exit translocation in bacteria and eukaroytes differ?

A

EFG (bacteria)/ eEF2 (eukaryotes)

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15
Q

General mechanism of termination

A

Stop codon recognised by release factors

  • > 1 end A site, the other changes conformation of active site in large sub-unit
  • > hydrolytic reaction -> growing polypeptide released
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16
Q

How do release factors differ in bacteria from eukaryotes?

A

Bacteria - RF1/RF2 -> recognise UAA, UGA, UAG with overlapping specificity
RF1: UAA/UAG and RF2: UAA/UGA
Eukaryotes - eRF1 - recognises all 3

17
Q

Core polymerase: a2bb’w

What role do these sub-units have?

A

b’: core polymerase subunit (DNA binding)
b: core polymerase subunit (polymerase active
site)
a: scaffolding role
w: unknown role

18
Q

What is the sigma factor?

A

role in transcription initiation (promoter

recognition), main type is s70