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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
What happens during translocation (in elongation of translation in eukaryotes)?
dipeptidyl-tRNA (or from the 2nd cycle: peptidyl-tRNA) is placed onto P- site from A-site
26
Translocation is catalysed by?
translocase
27
Translocation needs?
• Translocation needs EF-2 + GTP complex (energy | consumption: GTP hydrolyses to GDP + Pin)
28
three nucleotides =
one codon
29
At the end of elongation:
* 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
What happens in the next cycle after Elongation of translation in eukaryotes`
• 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
What happens during Termination of translation (in pro- and eukaryotes) at stop codon?
At stop codon (UAA, UAG or UGA) no aminoacyl-tRNA can bind to A-site --> PRF protein binds to A-site instead
32
What is PRF?
PRF splits peptide chain of peptidyl-tRNA (GTP- consumption!) --> the newly synthesized protein chain gets free
33
What is the result after Termination of translation (in pro- and eukaryotes) at stop codon?
two ribosomal subunits and mRNA dissociate
34
What happens during Termination of translation (in pro- and eukaryotes) caused by PRF?
Deliberation of the newly synthesized protein chain and dissociation of ribosomal subunits caused by PRF
35
What happens during Initiation of translation in prokaryotes?
1. Small ribosomal subunit + IF-1 and IF-3 2. + 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
Where does Kozak-scanning take place?
- initiation of translation in eukaryotes | - NOT in in initiation of translation in prokaryotes
37
Major differences btw initiation of translation in prokaryotes compared with eukaryotes:
* 3 IF-s are needed only ↔ eukaryotes need more •Initiator (first) amino acid: N-formyl-methionine * No Kozak-scanning mechanism
38
Elongation factors in prokaryotes:
* EF-Tu | * EF-G
39
Elongation factors in eukaryotes:
* EF-1α | * EF-2
40
Transcription and translation happen simultaneously in?
Elongation of translation in prokaryotes
41
what happens during Elongation of translation in prokaryotes?
One mRNA binds to more than one ribosomes --> Translation happen parallelly from all gene transcripts of mRNA (polycistronic!) --> polyribosome
42
Polycistronic mRNA makes?
polyribosome | Elongation of translation in prokaryotes
43
Energy balance of translation: | - Initiation
1 GTP (in complex with eIF-2 or IF-2)
44
Energy balance of translation: | - Kozak-scanning mechanism
(eukaryotes only) | 1 ATP/nucleotide
45
Energy balance of translation: | - Elongation
4 ATP/amino acid
46
Where does the 4ATP/amino acid come from in Elongation?
• 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
Energy balance of translation: | - Termination
1 GTP (for PRF)
48
Energy balance of translation: | - Translocation
1 GTP (in complex with EF-2 or EF-G)

Biochem (14 decks)

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