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Cellular Composition > Protein Synthesis in prokaryotes > Flashcards

Protein Synthesis in prokaryotes Flashcards

1
Q

What is peptidyl tRNA?

A

tRNA which has a peptide attached to it

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2
Q

What is a svedberg unit?

A

A non-metric unit for density, a measure of the size of the particle

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3
Q

Which direction is mRNA translated in?

A

5’ to 3’

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4
Q

Which amino acid is used in intiation of protein synthesis in prokaryotes?

A

N-formyl methionine

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5
Q

What does polycistronic mean?

A

mRNA that encodes several proteins, all sit on the same mRNA but all have their own start and stop codons

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6
Q

What is the ribosome binding site in E.coli called?

A

Shine dalgarno sequence

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7
Q

What is required for translation initation in prokaryotes?

A

Ribosome binding sequences

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8
Q

How far are ribosome binding sites from start codons?

A

3-11 bases upstream (from the 5’ end)

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9
Q

Which part of the ribosome recognises the shine dalgarno sequence?

A

The 16s ribosomal sequence

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10
Q

How does the ribosome bind to the shine dalgarno sequence?

A

Watson-Crick (complementary) base pairing

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11
Q

Which site on the ribosome is the AUG start codon placed in?

A

The P site

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12
Q

What is required for the tRNA to associate to the small ribosomal subunit?

A

3 Initiation factors (IF1, IF2, IF3) and GTP

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13
Q

What ensures the specific modified methionine tRNA is recruited to the mRNA in initiation?

A

The initiation factors

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14
Q

How does the large ribosomal subunit bind during initiation?

A

The hydrolysis of GTP into GDP and Pi produces a conformational change within the large subunit to make it bind

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15
Q

What is required for elongation?

A

The elongation factor EF-Tu

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16
Q

Which site does aminoacyl tRNA bind to on the ribosome?

A

The A site

17
Q

Outline the steps of elongation

A
  1. Aminoacyl tRNA binds to empty A site
  2. Proofreading and EF-Tu dissociates
  3. Growing polypeptide chain is tranferred from peptidyl tRNA to aminoacyl tRNA
  4. Large subunit translocates
  5. Small subunit translocates
18
Q

What is being proofread in elongtion?

A

If base pairing between tRNA and mRNA is correct (therefore if the correct tRNA is bound)

19
Q

What is the primary function of EF-Tu?

A

To transport the correct aa-tRNA to the A site of the ribosome

20
Q

How is the peptide chain transferred from the tRNA in the p site to the tRNA in the A site?

A
  • Nucleophilic attack of bond between peptide and tRNA breaks it
  • Growing polypeptide chain transfers it to the amino group of the incoming aminocyl tRNA
21
Q

Does the transfer of the polypeptide require ATP? Why?

A

No as ATP has already been consumed by synthetase to attach the amino acid to the tRNA

22
Q

How does the ribosome move to free up the A site?

A
  • The large subunit translocates 3 nucleotides forward and is stabilised by elongation factor G
  • The small subunit then translocates
23
Q

Why does the large subunit have to be stabilised by elongation factor G when translocating?

A

The movement of the ribosome is energetically unfavourable

24
Q

What is used to stabilise the movement of the large ribosomal subunit?

A

Elongation factor G

25
Q

When is GTP used in translation?

A
  • At initiation
  • In proofreading during elongation
  • In the movement of the ribosome during elongation
26
Q

What happens when the small ribosomal subunit translocates?

A
  • Full E, P, A sites are reformed
  • Elongation factor hydrolyses GTP to provide energy
  • EF-G is released
27
Q

How does termination of translation occur in prokaryotes?

A
  • Stop codon is put in the A site
  • Release factor binds to stop codon
  • This causes conformational change in ribosome causing ribosome to come apart
28
Q

What is release factor?

A

A protein which mimicks tRNA

29
Q

What is the effect of release factor binding?

A
  • causes large and small ribosomal subunits to come apart
  • mRNA is released
  • Causes cleavage of final aminoacyl bond between tRNA and polypeptide
30
Q

In prokaryotes are transcription and translation coupled?

A

Yes

Cellular Composition (15 decks)

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