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Protein Synthesis > Steps In protein Synthesis > Flashcards

Steps In protein Synthesis Flashcards

1
Q

What direction is mRNA translated

A

-5’ -3’

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2
Q

What is translation

A

-assembly of amino acids from tRNA into a peptide chain sequence directed by mRNA template and done by ribosomes

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3
Q

List the 3 steps of translation

A

1 initiation
2 Elongation
3 termination

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4
Q

Which organism has translation and transcription linked, how and why

A
  • prokaryotes
  • translation starts before transcription is done
  • genetic material not separated from ribosomes via nucleus
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5
Q

What does initiation need before starting peptide formation and list them

A
  • assembly of components of translation
  • 2 ribosomal subunits
  • 1st aminoacyl-tRNA
  • mRNA bound to ribosomes
  • GTP
  • initiation factors
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6
Q

List the initiation factors in eukaryotes and prokaryotes and what they do

A

1 prokaryotes

  • IF 1
  • IF 2 GTP : beings charged met-tRNA to P site
  • IF 3 : prevents premature association of subunits

2 eukaryotes

  • eIF 3 : prevents immature association of subunits
  • eIF 2 GTP : beings charged met-tRNA to P site
  • eIF 4 : locates AUG along with small subunit
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7
Q

Mechanism by which ribosomes recognizes nucleotide sequence to initiate translation ( AUG )

A

1 Shine-Dalgarno sequence - E. coli has purine rich region 6-10 bases upstream of initiation codon
-16S rRNA component of 30S subunit has sequence complimentary to SD and binds to it

2 5’ cap - no SD sequence In eukaryotes. Small subunit ( 40S with eIF-4 proteins ) binds close to cap at 5’ and scans for AUG

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8
Q

Use of eIF-4 proteins near cap and poly A tail cap

A

-mediate circularization of the mRNA and prevent use of incompletely processed mRNA

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9
Q

How is met-tRNA bound to initiator codon and energy source and factors responsible

A
  • AUG recognized by special tRNA and IF-2-GTP ( pro ) and eIF-2-GTP ( eu ) factors binds it to AUG
  • GTP hydrolyzed to GDP
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10
Q

Special features of initiation tRNA

A
  • only one to go directly to P site

- only one recognized by eIF-2

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11
Q

What type of initiate tRNA and its aas is carried in prokaryotes

A

-N-formulated methionine

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12
Q

When and how is methionine N-formulated

A
  • after it has been added to tRNA
  • uses transformylase ( enzyme ) and N10-formyl-THF as carbon donor

-N10-formyl-THF is cleaved by enzyme and N-formly added to N link ( COH ) of methionine forming fMet-tRNA

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13
Q

What usually happens to methionine

A

-removed before translation is complete

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14
Q

What happens after net-tRNA has been bound to mRNA

A

/large subunits then joins complex and functional Ribosome formed with charged initiator tRNA

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15
Q

Function of guanine nucleotide exchange factor

A

-reactivates eIF-2-GTP and IF-2-GTP by replacing GDP with GTP

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16
Q

How does elongation occur in translation

A

-amino acids are added to carboxyl of present chain via amide ( peptide bond ) of incoming aas

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17
Q

What is decoding and mediator

A

-bringing of aminos up-tRNA next on template mRNA to A site

  • facilitated by EF-Tu-GTP and EF-Ts ( prokaryotes )
  • EF-1alpha-GTP and EF-l beta gamma ( eukaryotes )
18
Q

What catalyses peptide bond formation and where does it occur

A
  • peptidytransferase

- intrinsic to 23S rRNA in large subunit

19
Q

What is a ribozyme

A

-rRNA which catalyses a reaction

23S of large subunit in prokaryotes catalyses peptide formation

20
Q

Describe what happens after aas added and translocation and the protein mediators

A
  • after peptide bond formed P site tRNA now empty and A site tRNA has peptide chain
  • ribosomes moves 3 nucleotides towards 3’ end to next codon
  • EF-G-GTP ( prokaryotes)
  • EF-2-GTP ( eukaryotes)
21
Q

How is empty P site tRNA moved to E site and what else moves

A
  • through GTP dependent translocation

- A site tRNA with peptide chain now moves into P site

22
Q

How does termination occur

A

-when termination codon moves into A site

23
Q

What factors recognizes termination codon at A site and what do they do

A
  • RF-1/2 in prokaryotes
  • eRF in eukaryotes

-they bind to termination sequence and result in hydrolysis of bond linkage ester of tRNA and peptide leasing nascent chain

24
Q

What does RT-3-GTP and eRF-3 do

A

-hydrolytically remove RF-1/2 and eRF from termination signal

25
Q

Toxins and infections which can affect translation and describe what they do

A

1 streptomycin - binds to 30S subunit, distorts structure and interferes with protein synthesis

2 tetracyclines - interact with 30S subunit blocking acces of tRNA to A site and inhibit elongation

3 chloramphenicol - inhibits prokaryotic peptidytransferase activity ( aas from P to A tRNA ) high levels inhibit mitochondrial protein synthesis

4 puromycin - bears resemblance to tRNA. Accepts peptide from p site and inhibits elongation. Truncated protein made

5 erythromycin - binds irreversibly to site on 50S subunit blocks tunnel by which peptide leaves and inhibits elongation

6 diphtheria toxin - inactive EF-2 in eukaryotes thereby inhibiting translocation

26
Q

List elongation factors and what they do

A

Prokaryotes 1st and eukaryotes 2nd

1 brings all other charged tRNA’s to A site

  • EF Tu GTP
  • EF 1 alpha

2 guanine exchange factors ( replace GDP with GTP )

  • EF Ts
  • EF 1 beta gamma

3 translocation of ribosomes along mRNA

  • EF G GTP
  • EF 2 GTP
27
Q

List release factors and what they do

A

Prokaryotic 1st and eukaryotes 2nd

1 recognizes stop codon and cuts peptide form tRNA

  • RF 1/2
  • eRF

2 releases other RF factors

  • RF 3 GTP
  • eRF 3 GTP
28
Q

How do polysomes form

A
  • due to the length of mRNA

- numerous Ribosomes can translate message at the same time

29
Q

Where is gene expression mainly regulated

A

-transcription phase

30
Q

How does translation phase regulate gene expression

A
  • modified eIF ( phosphorylated eIF 2 GTP is inactive )
  • proteins can bind to mRNA and inhibit its use by blocking translation or protect its use by protecting it from degradation
31
Q

What is protein targeting

A

-addition of amino acid sequences that direct peptide to its final destination

32
Q

What is co/post translational modifications, its effect and when does it occur

A
  • can occur during translation or after
  • covalently modify( adding chemical groups or trimming peptide chain ),folding or ubiquitinating a peptide chain to active or inhibit its function
33
Q

Describe trimming and its target

A
  • many proteins designated for secretions

- large inactive precursors have some parts removed by endoproteases activating them

34
Q

Describe covalent attachments

A

-they activate or inhibit a protein by a variety of covalent attachments

35
Q

Describe phosphorylation and its target

A

-addition of phosphate group to OH of serine, Threonine or Tyrosine

36
Q

What catalyses and reverses phosphorylation

A
  • family of protein kinases

- cellular protein phosphateses

37
Q

Describe glycosylation and its target

A
  • proteins to become part of membrane or secreted
  • sugar added to amide nitrogen of asparagine ( n-linked )
  • sugar built on OH group of serine and threonine
38
Q

Describe hydroxylation ,where done and target

A
  • done In sER

- collagen residues lysine and proline have OH added to them by vitamin C dependent hydroxylases

39
Q

Describe carboxylation and function and example

A
  • to active proteins
  • carboxyl group added by vitamin K dependent to glutamate

-g carboxyglutamate Gla essential for blood clotting proteins

40
Q

Describe biotin addition

A

-covalently added to e amino group of lysine

41
Q

Describe addition of lipids and function and special features

A
  • Farnesyl group help anchor protein at membrane

- can be acetylated at N end

42
Q

List the covalent additions, the others and the none covalently adding

A
  • glycosylation
  • hydroxylation
  • phosphorylation
  • adding biotin
  • adding lipids
  • carboxylation
  • trimming
  • folding
  • ubiquitinating

Protein Synthesis (8 decks)

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