2.4. Translation

Question 1

site of translation

Answer 1

ribosome

Question 2

subunits in eukaryotic and prokaryotic ribosome

Answer 2

eukaryotic ribosome : 60S and 40S = 80S
prokaryotic ribosome : 50S + 30S = 70S

Question 3

different ribosomal sites

Answer 3

(1) mRNA binding site : where mRNA is read
(2) aminoacyl or acceptor (A) site : tRNA + aa
(3) peptidyl or peptide (P) site : tRNA + growing polypeptide
(4) exit (E) site : tRNA that no longer have a bound aa exit from the ribosome
(5) catalytic site : covalent bond, specifically a peptide bond, are formed between two amino acids

Question 4

where is the peptide formed?

Answer 4

between the carbon of the carboxyl group of one amino acid and the nitrogen of the amino group of the other

the carboxyl group loses a hydroxyl group; amino group loses a hydrogen

Question 5

what is expelled when peptide bonds are formed?

Answer 5

water

Question 6

stages of translation

Answer 6

(1) initiation
(2) elongation
(3) termination

Question 7

short, ribosomal binding site found upstream (5’ end) of the start codon (AUG) in mRNA

Answer 7

shine-dalgarno sequence

Question 8

what happens during initiation in bacteria?

Answer 8

the 30S initiation complex is assembled from mRNA, initiatior tRNA, and the SSU.
(1) mRNA and initiator tRNA, carrying N-formylmethionine (fMet), bind to the SSU.
(2) initiation factors use energy from GTP to promote the addition of large ribosomal unit; initiation tRNA starts out in the P-site

Question 9

what happens during elongation and termination?

Answer 9

(1) elongation factors use GTP to install the incoming tRNA into the A-site
(2) peptide bond formation is then catalyzed by the peptidyl transferase activity
(3) translocation of the ribosome along the mRNA from one codon to the next requires hydrolysis of another GTP and results in movement of the tRNA with the growing peptide to the P-site
(4) the next charged tRNA binds to the A-site; cycle continues
(5) termination happens when the ribosome reaches any one of the three stop codons (UAG, UGA, UAA)

Question 10

shifting of the entire mRNA-tRNA complex in the direction of the P site by a distance of three nucleotides

Answer 10

translocation

Question 11

termination codon is recognized by ____ which binds to the A site and stimulates hydrolysis of the polypeptide from the peptidyl tRNA, leading to its release from the translation complex

Answer 11

release factors

video: release factors bind to termination codon, causing the release of polypeptide chain. ribosome translocates one last time. tRNA and rf exit the ribosomes, and the ribosomes dissociates

Question 12

true or false : in eukaryotes, translation is separated spatially and temporally from transcription.

Answer 12

true. in eukaryotes, transcription occurs in the nucleus, where DNA is transcribed into pre-mRNA. the mature mRNA is then transported to the cytoplasm for translation

Question 13

true or false : eukaryotic translation uses larger ribosomes.

Answer 13

true. eukaryotes use 60S and 40S, compared to 50S and 30S used by prokaryotes

Question 13

are rRNAs longer in eukaryotic translation?

Answer 13

yes. eukaryotic rRNA is longer, containing expansion segments (not present in prokaryotes) that are needed for ribosome assembly and translation regulation and specificity.

Question 14

is there a shine-dalgarno sequence in eukaryotic translation?

Answer 14

none. kozak sequence is often present, instead.

Question 15

initiation in eukaryotic translation
(1) initiation starts when the SSU associates with the m^7G cap
(2) several eukaryotic initiation factors (eIF) help in binding the SSU and the mRNA and in finding the start codon
(3) the initiatior tRNA carries an unformylated Met : tRNAiMet
(4) presence of kozak sequence surrounding the start codon enhances the efficiency of translation intiation

Answer 15

chrue

Question 16

what are involved in elongation and translation in eukaryotuc translation?

Answer 16

eukaryotic elongation factors (eEFs) and eukaryotic release factors (eRFs)

Question 17

what is required to form the initiation complex in eukaryotic translation?

Answer 17

poly-A binding proteins

Question 18

do eukaryotic mRNAs have a much longer half-life compared to bacterial mRNAs?

Answer 18

yes. eukaryotic mRNAs can live up to 10 hours, whereas bacterial mRNAs can only live for 5 minutes.

Question 19

advantages of closed-loop translation

Answer 19

(1) waste energy is prevented in translating partially degraded RNA : cell will not waste energy translating a partially degraded mRNA lacking either a cap or poly-A tail
(2) efficient ribosome recycling : ribosomes that complete synthesis of one polypeptide can dissociate from the mRNA and then reinitiate translation adjacent to the cap, which is short distance away in the loop

Question 20

why is formylation in bacteria important?

Answer 20

(1) formylation dictates tRNA (fMet) to engage in the initiation of translation : formylation marks the tRNA to be specifically used for the initiation of translation. it ensures that fMet-tRNA is recognized by IFs and the ribosome to start protein synthesis; distinguishes it from other tRNAs
(2) prevents the misappropriation of this tRNA by the elongation apparatus : for specificity, to maintain the accuracy of translation as it prevents the tRNA from being mistakenly used by the elongation apparatus during protein synthesis, since during elongation, other tRNAs bring amino acids to the ribosome to be added to the growing polypeptide chain; the formyl group on methionine prevents it from being used during elongation

Question 21

fMet was initially found in the translation process of
bacteria, chloroplast, and mitochondria. Moreover, fMet promotes protein complex formation in mitochondria and works as a degradation
signal in bacteria and yeast. Although the role of fMet in humans remains unresolved, a positive correlation between fMet, integrated stress
response, and late-onset diseases has been identified.

Answer 21

chrue