L21

Question 1

Which of the following is true about the difference between translation in prokaryotes and eukaryotes?

Only prokaryotes have an initiation factor that binds the 5′ cap structure on mRNAs

Only eukaryotic mRNAs initiate with a residue of N-formylmethionine

A Shine-Dalgarno sequence is needed for initiation of only eukaryotic mRNAs

Translation and transcription are coupled only in prokaryotes

Answer 1

Translation and transcription are coupled only in prokaryotes

Question 2

“Only prokaryotes have an initiation factor that binds the 5′ cap structure on mRNAs”

Answer 2

Incorrect because only eukaryotic mRNAs have a 5′ cap, and eukaryotic initiation factors (eIFs) bind it.

Question 3

“Only eukaryotic mRNAs initiate with a residue of N-formylmethionine”

Answer 3

Incorrect because N-formylmethionine (fMet) is used only in prokaryotes.

Eukaryotes start with methionine (Met).

Question 4

“A Shine-Dalgarno sequence is needed for initiation of only eukaryotic mRNAs”

Answer 4

Incorrect because the Shine-Dalgarno sequence is a prokaryotic ribosome-binding site.

Question 5

prokaryote ribosome

Answer 5

30S + 50S = 70S

Question 6

secondary structure complicated

Answer 6

rRNA

Question 7

folding of ribosomal subunit

Answer 7

highly conserved

Question 8

lie mainly on surface

Answer 8

ribosomal protein

Question 9

interface

Answer 9

few subunits than back

Question 10

APE

Answer 10

aminoacyl-tRNA
peptidyl-tRNA
Exit

Question 11

What is the role of the Shine-Dalgarno sequence?
It acts as a signal for the termination of translation.
It guides the 30S ribosome to the initiating (5′) AUG of the mRNA.
It marks the polypeptide for translocation into the lumen of the endoplasmic reticulum.
It targets proteins for degradation.

Answer 11

It guides the 30S ribosome to the initiating (5′) AUG of the mRNA.

Question 12

Eukaryotic polysomes do not contain
ribosomes
mRNA
polypeptides
DNA

Answer 12

DNA

Question 13

Signals that define the beginning and end of protein synthesis are contained in
rRNA
ribosome
mRNA
protein
tRNA

Answer 13

mRNA

Question 14

The steps required for peptide elongation at the ribosome are, respectively,
initiation, elongation, and release.
decoding, transpeptidation, and translocation.
initiation, elongation and termination.
aa-tRNA binding, GTP-peptidation, and translocation.

Answer 14

decoding, transpeptidation, and translocation.

Question 15

Which of the following is true about antibiotics?
They are artificial compounds that must be synthesized in a lab.
They are not effective in treating viral infections of humans.
All antibiotics target the ribosome.
They are equally toxic to prokaryotic and eukaryotic cells.

Answer 15

They are not effective in treating viral infections of humans.

Question 16

❌ “They are artificial compounds that must be synthesized in a lab.”

Answer 16

Many antibiotics are naturally produced by microorganisms (e.g., bacteria or fungi).

Question 17

❌ “All antibiotics target the ribosome.”

Answer 17

Some do, but many target other processes, such as:

Cell wall synthesis (e.g., penicillin)

DNA replication

Metabolic pathways

Question 18

❌ “They are equally toxic to prokaryotic and eukaryotic cells.”

Answer 18

Antibiotics generally show selective toxicity, meaning they target bacterial features that differ from eukaryotic cells.

Question 19

The peptidyl transferase activity that catalyzes peptide bond formation is found in
the large ribosomal RNA.
tRNAs.
the EF-G protein.
the 30S ribosomal subunit.

Answer 19

the large ribosomal RNA.

Question 20

EF-G can bind the A site of the ribosome because
its structure resembles an EF-Tu/tRNA complex.
it can base pair with the mRNA
its structure resembles that of EF-Tu.
it can form a complex with tRNA.

Answer 20

its structure resembles an EF-Tu/tRNA complex.

Question 21

Which of the following events occurs during the termination of polypeptide synthesis?
The polypeptide-containing tRNA dissociates from the ribosome.
Termination is initiated in response to a termination codon in the P site.
The ribosome dissociates into its 30S and 50S subunits.
A termination factor recognizes its unique cognate termination codon.

Answer 21

The ribosome dissociates into its 30S and 50S subunits.

Question 22

Which of the following is true about the proofreading mechanism on the ribosome?
Proofreading fidelity increases with the rate of protein synthesis.
The identity of the amino acid attached to tRNA is checked by the ribosome.
Proofreading occurs in the A site of the ribosome.
Proofreading occurs only after GTP hydrolysis.

Answer 22

Proofreading occurs in the A site of the ribosome.

Question 23

Please label [x, i, ii, iii, y] when polypeptide gets longer in y to x direction
A. [3’, 5’, A, P, E]

B. [5’, 3’, P, A, E]

C. [5’, 3’, A, P, E]

D. [3’, 5’, E, P, A]

E. [5’, 3’, E, P, A]

Answer 23

A. [3’, 5’, A, P, E]

Question 24

translation: ribosome read template strand which way?

Answer 24

5’ to 3’

Question 25

In E. coli, how is a specific AUG identified as a start codon? You can respond once A. A sequence known as the TATA box is located approximately 10 nucleotides upstream of the AUG codon. B. A purine rich sequence known as the Shine-Dalgarno sequence is located approximately 10 nucleotides upstream of the AUG codon. C. Enhancer sequences are found in the promoter region and help identify the AUG codon. D. The ribosome binds the 7-methylguanosine cap at the 5’ end of a mRNA and moves 3’ until it runs into the first AUG.

Answer 25

B. A purine rich sequence known as the Shine-Dalgarno sequence is located approximately 10 nucleotides upstream of the AUG codon.

Question 26

Which of the following proteins do NOT bind the ribosome during protein synthesis? If ALL bind, choose E. You can respond once A. aminoacyl tRNA synthetases B. initiation factors C. elongation factors D. termination factors E. All bind

Answer 26

A. aminoacyl tRNA synthetases

Question 27

Which of the following statements best describes the ribosomal large subunit? Response recorded A. It binds the mRNA B. It detects and hydrolyzes discharged tRNAs C. It is made entirely of RNA D. It contains the peptidyltransferase center E. It finds the initiation codon without help from the small subunit

Answer 27

D. It contains the peptidyltransferase center

Question 28

small ribosomal subunit

Answer 28

- binds the mRNA - detects and hydrolyzes discharged tRNAs - find initiation codon

Question 29

large ribosomal subunit

Answer 29

- made of rRNA and proteins - catalyze peptide bond formation - contains the peptidyltransferase center, which forms peptide bonds between amino acids during translation.

Question 30

Puromycin inhibits translation by: Response recorded A. resembling an aminoacyl-tRNA and interfering with peptide transfer, which results in premature termination of translation. B. catalyzing ADP-ribosylation, and inactivation, of EF-Tu. C. catalyzing cleavage of the eukaryotic large subunit rRNA. D. inhibiting prokaryotic aminoacyl-tRNA binding to the ribosome small subunit. E. inhibiting prokaryotic peptidyl transferase.

Answer 30

A. resembling an aminoacyl-tRNA and interfering with peptide transfer, which results in premature termination of translation.

Question 31

tetracyclin

Answer 31

antibiotic inhibiting prokaryotic aminoacyl-tRNA binding to the ribosome small subunit.

Question 32

What is the minimal energy cost of a peptide bond (in terms of high-energy phosphates)? Response recorded A. 0 B. 1 C. 2 D. 3 E. 4 F. 5

Answer 32

E. 4

Question 33

Which of the following most accurately describes the relative abundance (by total mass) of RNA species inside cells? This poll is locked. A. mRNA < rRNA < tRNA B. mRNA < tRNA < rRNA C. rRNA < tRNA < mRNA D. tRNA < mRNA < rRNA E. tRNA < rRNA < mRNA

Answer 33

B. mRNA < tRNA < rRNA

Question 34

What happens to proteins after they are made?

Answer 34

The N-terminus of the growing polypeptide worms through an exit tunnel in the large subunit

Question 35

What is the function of an N-terminal hydrophobic signal sequence in protein synthesis? You can respond once A. To designate a protein for transport to Golgi rather than stay within endoplasmic reticulum B. To designate a protein for synthesis at the rough ER. C. To indicate proteins that should be glycosylated D. To indicate proteins that must bind molecular chaperones in order to fold properly E. To assist a protein with folding and retention in a membrane

Answer 35

B. To designate a protein for synthesis at the rough ER.

Question 36

if target ER, signal location?

Answer 36

N-terminal or internal

Question 37

if target mitochondrial matrix, signal location?

Answer 37

N-terminal (multiple)

Question 38

if target peroxisome, signal location?

Answer 38

C-terminal

Question 39

if target nucleus, signal location?

Answer 39

internal

Question 40

signal not removed if target is

Answer 40

peroxisome, nucleus, sometimes ER

Question 41

signal removed if target is

Answer 41

ER, mitochondrial matrix

Question 42

When does SRP pause translation? You can respond once A. When it binds to the SRP receptor. B. When it docks on the Sec61 translocon. C. When it binds a hydrophobic signal sequence? D. When the ribosome reaches a stop codon. E. After a signal sequence is cleaved off.

Answer 42

C. When it binds a hydrophobic signal sequence? SRP is ribonucleoprotein

Question 43

SRP 3 functions

Answer 43

- recognize signal sequence - pause translation - direct ribosome and nascent polypeptide to preprotein translocase channel on endoplasmic reticulum membrane - is ribonucleoprotein like ribosome and spliceosome