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Biochem > Translation > Flashcards

Translation Flashcards

1
Q

Translation=

A

Biosynthesis of proteins based on mRNA –> expression of genetic information

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2
Q

For translation the followings are needed:

A
  • mRNA: carries the genetic information
  • tRNA: transports activated amino acids for translation
  • Ribosome: subcellular organ where translation takes place
  • Numerous protein factors
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3
Q

Structure of tRNA (transfer RNA):

A
  • Intramolecular base pairing –> double stranded sections

* Three loops (~shamrock shape)

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4
Q

What does the Three lopps (- shamrock shape) of the tRNA consist of?

A
  • DHU-loop
  • Anticodon-loop
  • TφC-loop
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5
Q

function of DHU-loop:

A

binds aminoacyl-tRNA-
synthetase
• Contains dihydro-uridin-monophosphate (no double bond in uracil)

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6
Q

function of Anticodon-loop:

A

binds codons of mRNA

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7
Q

Function of TφC-loop:

A

binds large subunit of ribosome
• T = thymidine-monophosphate (thymine in RNA!)
• Φ = pseudouridine-monophosphate (uracil binds to ribose with C atom 5)

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8
Q

Funciton of 3’-end: CCA-sequence?

A

binds carboxylgroup of transported amino acid with ester bond

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9
Q

Binding of adequate amino acid with the 3’- CCA-sequence of tRNA:

A

Aminoacyl-tRNA-synthetase: specific for the tRNA and for the amino acid
• Aminoacyl-tRNA-synthetase binds ATP
• ATP+Amino acid –> aminoacyl-AMP + Ppin
- Aminoacyl-AMP: the amino acid binds to the phosphate group of AMP with acid anhydrid bond
• Aminoacyl-tRNA-synthetase binds to the DHU loop of tRNA
• Aminoacyl-AMP + tRNA –> aminoacyl-tRNA + AMP
- Aminoacyl-tRNA: the amino acid binds to the 3-OH-group of the ribose of AMP at CCA-sequence of 3’-end of tRNA

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10
Q

Ribosome is composed of?

A

ribosomal RNA molecules (rRNA) and proteins

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11
Q

Different types of rRNA can be characterised according to their ?

A

sedimentation coefficients (unit is Svedberg = S)

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12
Q

Large subunits of Ribosomes:

A

• Eukaryotes: 5S rRNA; 5,8S rRNA; 28S rRNA + 49
protein
• Prokaryotes: 5S rRNA; 23S rRNA + 34 protein

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13
Q

Small subunits of Ribosomes:

A
  • Eukaryotes: 18S rRNA +33 protein

* Prokaryotes: 16S rRNA + 21 protein

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14
Q

Binding sites of large ribosomal subunit:

A 
A = Aminoacyl-tRNA
P = Peptidyl-tRNA
E = Exit
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15
Q

Binding site of small ribosomal subunit:

A

mRNA-binding site

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16
Q

Translation in eukaryotes:

- place

A

• Cytoplasma
(mRNA have to transport out from the nucleus)
–> Rough endoplasmatic reticulum

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17
Q

Initiation of translation in eukaryotes:

A
  1. Small ribosomal subunit + eIF-2-GTP + other eIF-s + tRNAMet –> Prae-initiation complex
  2. Kozak-scanning mechanism: the prae-initiation complex rolls along the mRNA searching for the start codon: AUG = methionine-codon (energy consumption: 1 ATP/nucleotide)
  3. Recognised start codon –> small ribosomal subunit (18S rRNS) binds to the Kozak-sequence of mRNA
  4. GTP bound to eIF-2 hydrolyses to GDP + Pin –> large ribosomal subunit binds to the small one and all the eIF-s dissociate

–> Initiation complex

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18
Q

Elongation of translation in eukarytoes, at the end of initiation:

A

• Initiation complex –> methionyl-tRNA binds to the P-
site of large subunit with its TφC-loop
• A-site of large ribosomal subunit is free

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19
Q

Elongation consists of cycles:

A
  • All cycles have three steps

* Peptide chain gets longer by one amino acid in each cycle

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20
Q

EF-1α + GTP complex is needed for?

A

binding (energy consumption: GTP hydrolyses to GDP + Pin) (EF = elongation factor)

(Elongation of translation in eukaryotes)

21
Q

Aminoacyl-tRNA binds to the?

A

A-site of large ribosomal subunit with its TφC-loop and to the next codon of mRNA with its anticodon- loop (only that aminoacyl-tRNA can bind of wich anticodon-loop is complementary to the codon of mRNA)

(Elongation of translation in eukaryotes)

22
Q

Methionin is placed onto?

A

Methionin (or from the 2nd cycle: the peptide chain) is placed from the methionyl-tRNA (or from the 2nd cycle: peptidyl-tRNA) onto the newly bound aminoacyl-tRNA (P􏰁A): peptidyl- transferase

(Elongation of translation in eukaryotes)

23
Q

Peptidyl-transferase i a?

A

is a ribozym: this is the 28S rRNA of large ribosomal subunit
Peptidyl-transferase needs NO energy for this step

24
Q

What happens when Methionin i bound to peptidyl transferase?

A
  • By this step, a new peptide (amide) bond is formed betweeen methionine (or from the 2nd cycle: the peptide chain) and the newly bound amino acid (aminoacyl-tRNA) 􏰁 dipeptidyl-tRNA (or from the 2nd cycle: longer peptidyl-tRNA)
  • The „empty” tRNA goes to E-site from P-site 􏰁 then it dissociates

(Elongation of translation in eukaryotes)

25
Q

What happens during translocation (in elongation of translation in eukaryotes)?

A

dipeptidyl-tRNA (or from the 2nd cycle: peptidyl-tRNA) is placed onto P- site from A-site

26
Q

Translocation is catalysed by?

A

translocase

27
Q

Translocation needs?

A

• Translocation needs EF-2 + GTP complex (energy

consumption: GTP hydrolyses to GDP + Pin)

28
Q

three nucleotides =

A

one codon

29
Q

At the end of elongation:

A
  • Dipeptidyl-tRNA (or from the 2nd cycle: peptidyl-tRNA) binds to the P-site of large ribosomal subunit with its TφC- loop
  • A-site of large ribosomal subunit is free
30
Q

What happens in the next cycle after Elongation of translation in eukaryotes`

A

• Binding of new aminoacyl-tRNA to A-site
• Peptidyl-transferase –> tripeptidyl-tRNAonA-site
• Translocation –> tripeptidyl-tRNA is placed onto P-site from A-site –> A-site gets free
–> similarly in all cycles
- Peptide chain grows by one amino acid in each cycle

31
Q

What happens during Termination of translation (in pro- and eukaryotes) at stop codon?

A

At stop codon (UAA, UAG or UGA) no aminoacyl-tRNA can bind to A-site –> PRF protein binds to A-site instead

32
Q

What is PRF?

A

PRF splits peptide chain of peptidyl-tRNA (GTP- consumption!) –> the newly synthesized protein chain gets free

33
Q

What is the result after Termination of translation (in pro- and eukaryotes) at stop codon?

A

two ribosomal subunits and mRNA dissociate

34
Q

What happens during Termination of translation (in pro- and eukaryotes) caused by PRF?

A

Deliberation of the newly synthesized protein chain and dissociation of ribosomal subunits caused by PRF

35
Q

What happens during Initiation of translation in prokaryotes?

A
  1. Small ribosomal subunit + IF-1 and IF-3
    • IF-2-GTP + tRNAini + mRNA
      –> 30S initiation complex
      No Kozak-scanning, small ribosomal subunit (16S rRNA) binds to the Shine-Dalgarno- sequence (RBS = ribosome binding site) of mRNA
  3. IF-1 and IF-3 dissociate, GTP hydrolyses –> large ribosomal subunit binds
    - -> 70S initiation complex
36
Q

Where does Kozak-scanning take place?

A
  • initiation of translation in eukaryotes

- NOT in in initiation of translation in prokaryotes

37
Q

Major differences btw initiation of translation in prokaryotes compared with eukaryotes:

A
  • 3 IF-s are needed only ↔ eukaryotes need more •Initiator (first) amino acid: N-formyl-methionine
  • No Kozak-scanning mechanism
38
Q

Elongation factors in prokaryotes:

A
  • EF-Tu

* EF-G

39
Q

Elongation factors in eukaryotes:

A
  • EF-1α

* EF-2

40
Q

Transcription and translation happen simultaneously in?

A

Elongation of translation in prokaryotes

41
Q

what happens during Elongation of translation in prokaryotes?

A

One mRNA binds to more than one ribosomes –> Translation happen parallelly from all gene transcripts of mRNA (polycistronic!) –> polyribosome

42
Q

Polycistronic mRNA makes?

A

polyribosome

Elongation of translation in prokaryotes

43
Q

Energy balance of translation:

- Initiation

A

1 GTP (in complex with eIF-2 or IF-2)

44
Q

Energy balance of translation:

- Kozak-scanning mechanism

A

(eukaryotes only)

1 ATP/nucleotide

45
Q

Energy balance of translation:

- Elongation

A

4 ATP/amino acid

46
Q

Where does the 4ATP/amino acid come from in Elongation?

A

• For the activation of amino acid: 2 ATP
(ATP →AMP+PPin, for the resynthesis the energy of 2 ATPs are needed)
• Binding of aminoacyl-tRNA to A-site:
1 GTP (in complex with EF-1α or EF-Tu)
• Translocation: 1 GTP (in complex with EF-2 or EF-G) •

47
Q

Energy balance of translation:

- Termination

A

1 GTP (for PRF)

48
Q

Energy balance of translation:

- Translocation

A

1 GTP (in complex with EF-2 or EF-G)

Biochem (14 decks)

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