TRANSLATION

Question 1

genetic code

Answer 1

Code is triplet.
Code is non-overlapping. Each nucleotide
is part of only one codon and is read only once.
Code is almost universal. Most codons
have the same meaning in different organisms
(e.g., not true for mitochondria).
Code is degenerate. Met and Trp are the only exceptions.

Question 2

The clover leaf form of tRNA

Answer 2

1. The 5’-terminal phosphate group.
2. The acceptor stem is a 7-bp stem made by the base pairing of the 5’-terminal nucleotide with the 3’-terminal nucleotide (which contains the CCA 3’-terminal group used to attach the amino acid).
3. The CCA tail is a CCA sequence at the 3’ end of the tRNA molecule. This sequence is important for the recognition of tRNA by enzymes critical in translation. In eukaryotes, the CCA sequence is added during processing and therefore does not appear in the tRNA gene.
4. The D arm is a 4 bp stem ending in a loop that often contains dihydrouridine.
5. The anticodon arm is a 5-bp stem whose loop contains the anticodon.
6. The T arm is a 5 bp stem containing the sequence TΨC where Ψ is a pseudouridine.
7. Bases that have been modified, especially by methylation, occur in several positions outside the anticodon. The first anticodon base is sometimes modified to inosine (derived from adenine)

Question 3

Amino acid activation

Answer 3

Amino acids are attached to their corresponding tRNAs by an ester bond to give aminoacyl-tRNAs.
This is catalyzed by aminoacyl-tRNA synthetases.
The reaction is downhill, ensuring irreversibility:

Question 4

Wobbling

Answer 4

Two different leucine codons (CUC, CUU) can be read by the same leucine tRNA molecule, contrary to regular base-pairing rules.

Question 5

Initiation prokaryotes

Answer 5

Shine-Delgarno (SD) site consists of 3-9 contiguous bases in the mRNA that base pair with the 3’ end of 16S rRNA
and is located optimally 5 nt upstream of the initiator codon

Question 6

Initiation Eukaryotes

Answer 6

first AUG codon

downstream of the 5’ cap

Question 7

Peptide bond formation

Answer 7

synthesis of the peptide bound is catalyzed by an adenin in 23S RNA

Question 8

Termination

Answer 8

Proteins known as “release factors” recognize the stop codon (UGA, UAG, or UAA) at the A site
In E. coli RF-1 recognizes UAA and UAG, RF-2 recognizes UAA and UGA.
RF-3 binds GTP and enhances activities of RF-1 and –2.
Presence of release factors with a nonsense codon at A site transforms the peptidyl transferase into a hydrolase, which cleaves the peptidyl chain from the tRNA carrier
Hydrolysis of GTP is required for disassociation of RFs, ribosome subunit and new peptide

Question 9

Translation Initiation – Eukaryotes

Answer 9

Eukaryotic Initiation Factors (eIF4A, eIF4B, and eIF4G) associate with the 5’ cap, the 40S subunit, and initiator tRNA
Complex moves 5’ to 3’ unwinding the mRNA until an initiation site (AUG) is discovered
Initiation factors are released and 60S subunit binds

Question 10

inhibition

Answer 10

Inhibition of translation through phosphorylation of eIF2
Chloroamphenicol
puromycin
ricin
dipheria

Question 11

elongation

Answer 11

AAs are Brought to A-Site by tRNA Bound to eEF1A • GTP

Question 12

EF-TU

Answer 12

tRna inserted at A site , GTP in pro

Question 13

Ef-ts

Answer 13

helps releasing EF-tu and hydrolysis GTP in pro

Question 14

EF-G

Answer 14

tRNa from asite to p site in pro

Question 15

EF-1 aplha

Answer 15

tRna inserted at A site , GTP in eu

Question 16

EF-1 beta gamma

Answer 16

helps releasing EF-1 aplha in eu

Question 17

EF-2

Answer 17

tRNa from asite to p site in eu

Question 18

eRF

Answer 18

Binds to A site catalysing clevage of a.a from tRNA, poly p relased
ribosome dissociatea

Question 19

Rf1 RF2

Answer 19

recognized UAA, UAG, RF2. UAA, UGA

Question 20

RF3

Answer 20

hydrolysis of GTP

Question 21

FOrmation of ester bond to get aminoacyl-tRNA

Answer 21

aminoacyl-tRNA synthetases.

Question 22

Sequence in mRNA eukaryotic between cap and start of translation

Answer 22

apo B

Question 23

eIF2

Answer 23

eIF2 binds to GTP and forms a complex with Met-tRNA initiator.

• This complex (ternary complex = TC) docks on small subunit (40S) forming 43S PreInitiation Complex (PIC).
• TC scans the mRNA until the first start codon AUG.

Question 24

eIF2α

Answer 24

When cell is under stress, eIF2α is phosphorylated. This inactivates GTP recycling protein eIF2B. Prevents formation of 43S PIC => blocks protein synthesis.

Question 25

eIF4

Answer 25

• eIF4F = eIF4A+G+E = cap binding complex

- eIF4F binds to the mRNA G-cap (5’) by the 4E part of complex.

Question 26

cistron

Answer 26

a section of a DNA or RNA molecule that codes for a specific polypeptide in protein synthesis.

Question 27

how many tRNA needed to recognize all a.a codons

Answer 27

32 tRNAs

Question 28

3’-UTR

Answer 28

A section of (mRNA) that follows the translation termination codon. It contains regulatory regions that post-transcriptionally influence gene expression.

can influence polyadenylation, translation efficiency, localization, and stability of the mRNA. IT contains both binding sites for regulatory proteins And microRNAs that degrade RNA

Question 29

(elF) 4A

Answer 29

A helicase elF4A during translation initiation is to unwind the mRNA secondary structure in the 5’ UTR to facilitate ribosome binding

Question 30

eIF4E

Answer 30

directing ribosomes to the cap structure of mRNAs.

rate-limiting component of the eukaryotic translation