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Flashcards in Translation Deck (48)
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1

Translation=

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

2

For translation the followings are needed:

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

3

Structure of tRNA (transfer RNA):

• Intramolecular base pairing --> double stranded sections
• Three loops (~shamrock shape)

4

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

- DHU-loop
- Anticodon-loop
- TφC-loop

5

function of DHU-loop:

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

6

function of Anticodon-loop:

binds codons of mRNA

7

Function of TφC-loop:

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

8

Funciton of 3’-end: CCA-sequence?

binds carboxylgroup of transported amino acid with ester bond

9

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

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

10

Ribosome is composed of?

ribosomal RNA molecules (rRNA) and proteins

11

Different types of rRNA can be characterised according to their ?

sedimentation coefficients (unit is Svedberg = S)

12

Large subunits of Ribosomes:

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

13

Small subunits of Ribosomes:

• Eukaryotes: 18S rRNA +33 protein
• Prokaryotes: 16S rRNA + 21 protein

14

Binding sites of large ribosomal subunit:

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

15

Binding site of small ribosomal subunit:

mRNA-binding site

16

Translation in eukaryotes:
- place

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

17

Initiation of translation in eukaryotes:

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

18

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

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

19

Elongation consists of cycles:

• All cycles have three steps
• Peptide chain gets longer by one amino acid in each cycle

20

EF-1α + GTP complex is needed for?

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

(Elongation of translation in eukaryotes)

21

Aminoacyl-tRNA binds to the?

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

Methionin is placed onto?

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

Peptidyl-transferase i a?

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

24

What happens when Methionin i bound to peptidyl transferase?

• 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