Deck 6: Protein Synthesis: Translation and Posttranslational Modifications

Question 1

At which stage during the translocation of a protein destined to become an integral membrane protein is its polarity (for example, N-terminus cytoplasmic; C-terminus extracellular) determined?

A) during translation, by the polarity of association with signal recognition particle.
B) during translocation into the endoplasmic reticulum.
C) during translocation into the cis?Golgi.
D) during translocation into the trans?Golgi.
E) during translocation into the plasma membrane.

Answer 1

during translocation into the endoplasmic reticulum.

Question 2

Which statement is true?

A) ribosomes can bind to mRNA in prokaryotes while the RNA is still being synthesized.
B) Translation terminates in some cases due to the action of Rho factor.
C) In eukaryotes most of the proteins are made in the nucleus because that is where RNA is made.
D) If the base sequence in the anti-codon loop is altered, the amino acid-tRNA synthetase will add the wrong amino acid to the tRNA.
E) If the codon sequence is AUG the anti-codon sequence of the tRNA which recognizes AUG must be UAC.

Answer 2

ribosomes can bind to mRNA in prokaryotes while the RNA is still being synthesized.

Question 3

ATP is required in protein biosynthesis for

A) movement of mRNA on the ribosome.
B) activation of the amino group for peptide bond synthesis.
C) formation of aminoacyl-AMP.
D) attachment of transfer RNA to the ribosome.
E) proofreading the nascent polypeptide chain.

Answer 3

formation of aminoacyl-AMP.

Question 4

Chemical conversion of the cysteine residue in cys-tRNAcys to alanine, to yield ala-tRNAcys, results in:

A). a change in reading frame of the mRNA because of failure of the amino acid to match its codon.
B) incorporation of ala residues in proteins where cys was encoded.
C) incorporation of cys residues in proteins where ala was encoded.
D) premature termination at the site where the first cys was encoded.
E) utilization of an alternate cys-tRNA, available because of the degeneracy of the code.

Question 5

The degradation of cytosolic proteins is generally carried out by which of the following?

A) lysosomes
B) mitochondria
C) proteosomes
D) peroxisomes
E) trypsin

Question 6

The anticodon refers to a nucleotide sequence that

A) specifies translation initiation.
B) specifies translation termination.
C) covalently binds amino acids.
D) hydrogen bonds with mRNA.
E) hydrogen bonds with rRNA.

Question 7

Cycloheximide inhibits protein synthesis carried out by which type of ribosomes?

A) 70S
B) Mitochondrial
C) Chloroplast
D) 80S
E) All of the other answers are correct.

Question 8

Which component of the system for protein synthesis actually translates the nucleotide code to an amino acid code?

A) Messenger RNA
B) Transfer RNA
C) RNA polymerase
D) DNA polymerase
E) ribosomal RNA

Question 9

Signal recognition particle:

A) arrests transcription elongation.
B) arrests translation elongation.
C) catalyzes the removal of signal sequences.
D) is the eukaryotic equivalent of the docking protein.
E) catalyzes translocation of nascent polypeptides across the mitochondrial membrane.

Question 10

Which of the following gene mutations will always lead to a shortened protein?

A) missence mutation
B) nonsense mutation
C) frameshift mutation
D) deletion mutation

Question 11

Codons on mRNA may be accurately described by all of the following EXCEPT

A) they are read in a non-overlapping fashion.
B) they can form hydrogen bonds with tRNA.
C) they may specify initiation points.
D) in some cases they may be read by proteins rather than by tRNA's.
E) the same codon may specify more than one amino acid.

Question 12

Proteosomes are multifunctional, multisubmit protein complexes that

A) convert amino acids to glucose and ketone bodies during starvation.
B) degrade most cellular proteins to their consistent amino acids.
C) facilitate the endocytosis of lipoproteins by most cells.
D) participate in the digestion and absorption of dietary protein.
E) synthesize albumin and other plasma proteins in the liver.

Question 13

The genetic code is said to be redundant or degenerate. This means that

A) a single tRNA can mediate the addition of several different amino acids to the growing protein chain.
B) for each type of amino acid, there is only one transfer RNA which can mediate its addition to the growing protein chain.
C) three amino acids in the protein chain are specified by each codon.
D) three bases in mRNA are required to specify one amino acid in the protein chain.
E) there may be more than one codon for a given amino acid.

Question 14

The purine? rich Shine?
Dalgarno sequence in prokaryotic mRNA functions to

A) base pair with the A?T rich Pribnow box.
B) bind sigma factor.
C) base pair with transfer RNA.
D) facilitate the initiation of protein synthesis.

Question 15

The first step in protein synthesis that distinguishes a protein to be secreted from one to be retained in the cytoplasm is:

A) attachment of the ribosome to a membrane.
B) removal of signal sequences by signal peptidase.
C) binding of the signal recognition particle to the signal sequence.
D) binding of the fmet-tRNA to the ribosome.
E) binding of specialized ribosomes to the mRNA.

Question 16

The degeneracy of the genetic code refers to:

A) the possibility of tolerated mispairing in the third position of the codon.
B) the universal utilization of the same genetic code across all life forms on earth.
C) the observation that multiple codons specify the same amino acid.
D) the utilization of AUG for two functions (start and methionine).
E) codon usage for both amino acid specification and punctuation (start and stop).

Question 17

A polyribosome

A) is a group of ribosomes bound to a single polypeptide chain.
B) is an organized array of ribosomes on the surface of a membrane.
C) is a number of ribosomes engaged in translating the same mRNA molecule.
D) must be formed for protein synthesis to proceed.
E) None of the above.

Question 18

How many amino acids would the following eukaryotic mRNA encode? 5'-cap-AGCUACCGUAUGCAUGAUAAAGUGACCAUGCUGACAUGAUAAUAGGAG-3'-poly(A)?

A) 3
B) 8
C) 9
D) 10
E) 11

Question 19

The signal peptide is:

A) found on precursors to plasma proteins.
B) encoded nearer to the end than the 5' end of mRNA.
C) synthesized after the ribosome binds to the rough ER.
D) found nearest the carboxyl terminus of proteins.
E) found nearest the amino terminus of soluble cytoplasmic proteins.

Question 20

What two reactions are catalyzed by aminoacyl tRNA synthetases?

A) amino acid charging and tRNA phosphorylation
B) amino acid activation and tRNA charging
C) amino acid decarboxylation and tRNA charging
D) amino acid charging and tRNA activation

Question 21

During initiation of protein synthesis in prokaryotic and eukaryotic systems, GTP is hydrolyzed

A) to GMP when mRNA joins the ribosome.
B) to GMP when the large ribosomal subunit joins the growing initiation complex.
C) to GDP when mRNA joins the ribosome.
D) to GDP when the large ribosomal subunit joins the growing complex.
E) none of the above

Question 22

Which of the following statements regarding translation is INCORRECT?

A) The first amino acid introduced into the protein is MET.
B) mRNA serves as the template for protein synthesis.
C) tRNA serves to decode the genetic code located in the mRNA through interactions between the anticodon of the tRNA and the codons in the mRNA.
D) The mRNA is translated in the 5' to direction.
E) Proteins are synthesized in the carboxyl to amino direction.

Question 23

Plasma membrane proteins contain a signal sequence and

A) a stop-transfer peptide sequence.
B) mannose-6-phosphate.
C) a nuclear localization signal.
D) a docking protein sequence.
E) a KDEL sequence.

Question 24

Wobble

A) refers to the fact that some amino acids have multiple codons.
B) results in misreading of the genetic code.
C) allows one tRNA species to be charged with different amino acids.
D) results from a mutation in the anticodon.
E) allows several codons to be read by the same tRNA.

Question 25

Each of the following is considered to be an important stage in protein synthesis EXCEPT which one?

A) peptide chain elongation
B) peptide chain termination
C) peptide chain activation
D) amino acid activation
E) peptide chain initiation

Question 26

The genetic code

A) is overlapping.
B) varies greatly as one goes from viruses to higher organisms.
C) contains only amino acid signals.
D) consists of 64 possible codons, all of which are known.

Question 27

Each of the following is true for initiation of translation in eukaryotes EXCEPT

A) initiation involves binding of initiator tRNA to the small ribosomal subunit.
B) initiation involves binding of the small ribosomal subunit to the 5' cap.
C) phosphorylation of the initiation factor elF2 is required for initiation.
D) recognition of the initiation codon in mRNA is carried out by initiator tRNA.

Question 28

Which of the following is the anticodon for the initiator codon? (all written 5' to 3')

A) TAC
B) CTA
C) UAC
D) CAT
E) CUI

Question 29

Aminoacyl tRNA synthetases

A) splice tRNA molecules.
B) attach amino acids to a ribose of tRNAs.
C) attach a CCA to tRNAs.
D) always recognize the codon on the tRNA.
E) require no energy input for their action.

Question 30

Which of the following is true concerning the structure of tRNA?

A) molecular weight greater than 10 million
B) many modified bases
C) anticodon loop near the amino acid binding site
D) linear structure with no H-bonding between bases
E) -CCA sequence at 5' end

Question 31

Which of the following is required for translocation of peptidyl-tRNA from the A site to the P site?

A) ATP
B) GTP
C) dATP
D) None of these

Question 32

Mutations associated with I-cell disease result in which of the following functional defects?

A) incomplete translation of hydrolytic enzymes
B) abnormal secretion of extracellular enzymes
C) rapid degradation of cytosolic hydrolases
D) abnormal targeting of intracellular enzymes

Question 33

Covalent cross-linking in collagen is initiated by the formation of reactive aldehyde groups. Which of the following enzymes catalyzes the formation of these aldehyde groups?

A) lysyl oxidase
B) lysyl hydroxylase
C) prolyl hydroxylase
D) procollagen peptidase
E) none of the above

Question 34

I-cell disease is caused by a defect in a

A) glycosyltransferase.
B) methyltransferase.
C) kinase.
D) glycosidase.
E) peptidase.

Question 35

The Shine-Dalgarno sequence:

A) is an mRNA sequence element that is complementary to the 3'-end of 16S rRNA.
B) is a tRNA sequence element that is complementary to the 3'-end of 16S rRNA.
C) is an mRNA sequence element that H-bonds to the AUG start codon.
D) is an rRNA sequence that H-bonds to the AUG start codon.
E) is an mRNA sequence that H-bonds to itself to allow attenuation of transcription.

Question 36

All of the following statements regarding ribosomes are CORRECT EXCEPT

A) eukaryotic cytoplasmic ribosomes are more complex than prokaryotic ribosomes.
B) ribosomes are capable of binding two acylated tRNA molecules at the same time.
C) prokaryotic ribosomes resemble eukaryotic mitochondrial ribosomes.
D) eukaryotic cytoplasmic ribosomes contain 4 rRNA molecules.
E) the prokaryotic large ribosomal subunit contains a polynucleotide sequence which is complementary to a region of mRNA.

Question 37

Elongation of the asparagine-N-acetyl glucosamine oligosaccharide of glycoproteins takes place within

A) mitochondria.
B) lysosomes.
C) Golgi.
D) endoplasmic reticulum
E) cytosol.

Question 38

Activation of zymogens or proenzymes is often accomplished by

A) aggregation of monomers to form the active oligomer.
B) glycosylation reactions.
C) formation of covalent crosslinks.
D) hydrolysis of the peptide chain at a specific place.
E) the addition of a coenzyme to the structure.

Question 39

Degeneracy of the genetic code refers to

A) the collinear relationship between a gene and its encoded protein.
B) the existence of multiple species of tRNA.
C) the presence of introns within some, but not all, genes.
D) the fact that most amino acids are encoded by more than a single codon.
E) the fact that most codons code for more than a single amino acid.

Question 40

Methionine initiates protein synthesis

A) and thus every protein has a carboxy terminal methionine.
B) and thus every protein has an amino terminal methionine.
C) but is removed from most proteins before they become functional.
D) without being attached to a tRNA.

Question 41

Proteins are "tagged" for degradation by cytosolic proteases such as calpains through the covalent attachment of

A) ubiquitin
B) glutathione
C) glucose
D) pyridoxal phosphate
E) clathrin

Question 42

How many aminoacyl tRNA synthetases are required for protein synthesis?

A) one for each amino acid
B) one for each tRNA
C) one for each codon (excluding stop codons)
D) one for each amino acid plus each tRNA

Question 43

Protein synthesis:

A) requires a preexisting copy of the protein that is to be synthesized.
B) occurs at specialized ribosomes dedicated to synthesizing a single, specific protein.
C) occurs in generalized ribosomes that can synthesize any protein.
D) requires tRNA as the template containing the genetic information encoding the protein.
E) requires rRNA as the template containing the genetic information encoding the protein.

Question 44

During the process of peptide chain elongation, the growing peptide chain

A) is linked to the mRNA.
B) is linked to the ribosomal RNA.
C) is not linked at all to any RNA.
D) is linked to the OH of the adenosine terminal nucleoside of tRNA.

Question 45

The step in the biosynthesis of type I collagen which takes place after procollagen secretion from the cell is

A) glycosylation of hydroxyproline.
B) hydroxylation of lysine.
C) formation of disulfide crosslinks.
D) oxidation of lysine.
E) formation of triple helix.

Question 46

If AUG is the codon for methionine, which of the following sequences of bases (or their analogs) might be expected to be found somewhere on methionyl-tRNA?

A) CAU
B) UAC
C) AUG
D) GUA
E) None of the other answers is correct

Question 47

Which of the following deletions in the coding region of a gene would NOT result in a frameshift mutation?

A) one base-pair deletion
B) two base-pair deletion
C) three base-pair deletion
D) four base-pair deletion

Question 48

In protein biosynthesis

A) each amino acid recognizes its codon on the mRNA template because of structural specificity.
B) exactness of read-out is assured by the presence of traces of DNA on the ribosome.
C) each amino acid is first attached to tRNA that has an anticodon specific for the amino acid.
D) a given codon-anticodon pair must have identical base sequences to avoid the formation of degenerate proteins.
E) each amino acid recognizes its codon through recognition nucleotides in its specific transfer RNA molecule.

Question 49

Which of the following occurs when alanyl-tRNAser is added to a protein synthetic system?

A) Synthesis ceases at the first alanine codon.
B) Synthesis ceases at the first serine codon.
C) Alanine will be present in the serine positions of the completed protein.
D) Serine will be present in the alanine positions of the completed protein.
E) Alanine-tRNAser-EF1-GTP complex will not be formed.

Question 50

Approximately how many tRNA synthetases do most organisms have?

A) one synthetase for each triplet
B) one synthetase for each tRNA species
C) one synthetase for each peptide made
D) one synthetase for each amino acid

Question 51

All of the following statements about protein biosynthesis in eukaryotes are correct EXCEPT:

A) It occurs at the ribosomes.
B) Aminoacyl-tRNA synthetases are required.
C) Cycloheximide is an inhibitor.
D) A replication fork is required.
E) Energy is supplied by guanosine triphosphate.

Question 52

Diphtheria toxin is a potent inhibitor of protein synthesis. Which one of the following statements closely describes its mode of action?

A) It inhibits the binding of N-formyl methionine-tRNA to subunit of ribosomes.
B) It inhibits the peptidyl transferase activity of 50S subunit of ribosomes.
C) It catalyzes the transfer of adenosine diphosphate ribosyl moiety of NAD to the elongation factor EF-2.
D) It causes premature chain termination by covalent attachment of the toxin molecule to the growing polypeptide chain.
E) none of the above

Question 53

All of the following statements are TRUE about tRNA EXCEPT

A) Amino acids are directly attached to the 3'-OH of the terminal adenosine of tRNA.
B) Charging of tRNAs requires prior activation of amino acids involving hydrolysis of ATP.
C) The three-dimensional structure of tRNA depends on extensive intrachain hydrogen bonding (base pairing).
D) The anticodon sequence base pairs directly with ribosomal RNA.

Question 54

Which three amino acids are all known to undergo posttranslational modifications?

A) glutamine, valine, isoleucine
B) tyrosine, lysine, alanine
C) proline, glutamic acid, serine
D) aspartic acid, histidine, glycine
E) methionine, threonine, phenylalanine

Question 55

Suppose that you have the situation that the P site of the prokaryotic ribosome contains a tRNA to which is attached a peptidyl chain, and the A site contains a tRNA to which is attached an amino acid. What is the next step?

A) translocation of the mRNA relative to the ribosome by one codon
B) peptide bond synthesis
C) dissociation of the tRNA in the P site to allow movement of the tRNA from the A site to the P site
D) binding of a new aminoacyl-tRNA to the ribosome catalyzed by Tu
E) hydrolysis of the peptidyl chain from the tRNA

Question 56

All of the statements concerning initiation of translation in the eukaryotic system are TRUE EXCEPT

A) the IF-2.met-tRNAi.GTP complex binds to what will become part of the P site.
B) the small ribosomal subunit binds to the mRNA prior to the large subunit.
C) there are more initiation factors in this system than there are in prokaryotes.
D) the protein complex involved in this process will bind to the A site.
E) in reticulocytes, this process will be inhibited in the absence of heme.

Question 57

Which of the following statements is characteristic of the formation of an amino acyl tRNA?

A) An amino acyl adenylate is an intermediate.
B) ATP is a reactant.
C) Two different enzymes are involved in the process, one specific for tRNA and one specific for the amino acid.
D) A and B are both characteristic.
E) All of the above are characteristic.

Question 58

Regarding protein synthesis, which of the following statements is/are CORRECT?

A) There are three sites for tRNA attachment on the ribosomes called the D, R and S sites.
B) A nucleoside triphosphate involved in peptide chain elongation is GTP.
C) The amino acid residue placed during chain initiation on the N-terminus of proteins is serine.
D) Protein chain initiation in bacteria involves the interaction of the 20S, 25S and 50S ribosomal subunits.
E) All of the other answers are correct.

Question 59

Which of the following is not required for transport of a mitochondrial protein into the mitochondrion?

A) a matrix localization signal
B) an unfolded protein
C) a proton motive force
D) ATP
E) signal recognition particle

Question 60

Which of the following statements is(are) TRUE?

A) proinsulin is the first polypeptide intermediate in insulin biosynthesis
B) insulin has two disulfide bridges which may be reduced with full retention of activity
C) C-peptide is secreted in equimolar amounts as insulin
D) insulin must undergo post-translational modification
E) none of the above

Question 61

Transfer RNA (tRNA) is responsible for "decoding" the genetic information. This is a consequence of

A) tRNA being encoded by DNA.
B) tRNA secondary structure.
C) ribosomal secondary structure.
D) the anticodon and cognate amino acid being covalently part of the same tRNA molecule.
E) the structural similarity between tRNAs and specific amino acids.

Question 62

Codon-anticodon interactions

A) take place between mRNA and tRNA.
B) apply only to suppressor tRNAs.
C) involve base-pairing between mRNA and rRNA.
D) refer to interactions with the three termination codons.
E) involve base-pairing between tRNAs and amino acids.

Question 63

Peptide bonds are formed during protein synthesis between

A) the carboxyl group on peptidyl-tRNA and the amino group on aminoacyl-tRNA.
B) the carboxyl group on aminoacyl-tRNA and the amino group on peptidyl-tRNA.
C) the carboxyl group on a free amino acid and the amino group on aminoacyl-tRNA.
D) the carboxyl group on aminoacyl-tRNA and the carboxyl group on a free amino acid.
E) the carboxyl group on a free amino acid and the amino group on a free amino acid.

Question 64

The signal sequence is

A) a region on 18S rRNA which base pairs with mRNA.
B) the anti-codon sequence involved in wobble.
C) a hydrophobic amino acid-rich sequence at the amino terminal end of some proteins.
D) the sequence of mRNA for termination of translation.
E) None of the other answers is correct.

Question 65

aminoacyl tRNA synthetases

A) splice tRNA molecules.
B) attach amino acids to a ribose of tRNAs.
C) attach a 3' CCA to tRNAs.
D) always recognize the codon on the tRNA.
E) require no energy input for their action.

Question 66

The codon for formyl methionine tRNA will be

A) adjacent to that for the glycine codon.
B) the three terminal nucleotides.
C) randomly located in the mRNA.
D) the codon closest to the 5' terminus of the mRNA.
E) GCU.

Question 67

Post-translational modifications of amino acids include all the following EXCEPT which one?

A) disulfide bond formation
B) removal of methionine
C) protease cleavage
D) capping by 7-methylguanidine
E) attachment of prosthetic groups

Question 68

Some transfer RNA species are able to make use of two or more different codons because

A) they are able to carry two or more different amino acids.
B) some codon?anticodon interactions are limited to only two base pairs.
C) they can make use of a wobble base to base pair with different codons.
D) inosine is a common nucleoside in messenger RNA.

Question 69

Nonsense codons are the names given to the codons on the mRNA that signal

A) initiation.
B) elongation.
C) termination.
D) they are not on mRNA molecules.
E) none of the above

Question 70

Which of the following statements is correct concerning ubiquitin?

A) Ubiquitin occurs only in liver cells.
B) Covalent coupling of ubiquitin to a protein can mark that protein for degradation.
C) It is involved in transfer of mannose-rich oligosaccharides to proteins.
D) It is a transcription factor for RNA polymerase II.
E) it is an snRNP necessary for splicing of mRNA precursors.

Question 71

Translocation in protein synthesis is best defined as:

A) movement of a new aminoacyl-tRNA into the A site.
B) movement of the growing peptide chain from the tRNA in the P site to the tRNA in the A site
C) movement of the peptidyl-tRNA in the A site to the P site.
D) dissociation of the tRNA in the P site from the ribosome.
E) scanning of a ribosome along an mRNA in search of the initiation codon.

Question 72

Which of the following describes the function of the factor, rho? Rho is required for

A) RNA polymerase/promoter binding.
B) correct initiation of transcription.
C) correct termination of transcription.
D) catabolite repressor binding to promoters.
E) elongation of the growing RNA chain.

Question 73

The stop codon(s) for protein synthesis are

A) AAG, GGA.
B) UUU, GGG.
C) AAA, CCC, GGG.
D) AUG.
E) UAA, UGA, UAG.

Question 74

The antibiotics streptomycin, tetracycline, and erythromycin inhibit

A) charging of bacterial tRNAs.
B) enzymes involved in bacterial cell wall synthesis.
C) bacterial ribosome function.
D) bacterial RNA polymerase.

Question 75

In an aminoacyl-tRNA the amino acid is attached to the hydroxyl of the tRNA through

A) an amide bond.
B) an ester bond.
C) an anhydride bond.
D) a glycosidic bond.
E) an ether bond.

Question 76

During the synthesis of proteins on the rough endoplasmic reticulum (RER) signal peptidase cleaves the hydrophobic signal sequence

A) immediately after signal recognition protein (SRP) is bound.
B) when the SRP docks with the SRP receptor.
C) simultaneously with the release of the ribosome.
D) as the polypeptide chain is translocated through the membrane.
E) as the protein is secreted through the plasma membrane.

Question 77

Which of the following is an event occurring during the initiation of eukaryotic translation?

A) mRNA binding to the small ribosomal subunit
B) tRNA binding to the large ribosomal subunit
C) hydrolysis of ATP to ADP + Pi
D) peptide bond formation
E) a cap is added to the 5' end of the mRNA

Question 78

If a cell-free protein-synthesizing system from bacteria were supplied with aminoacyl-tRNAs rather than free amino acids, which of the following would NOT be required for peptide bond synthesis?

A) ATP
B) mRNA
C) ribosomes
D) peptidyl transferase
E) GTP

Question 79

Phenylalanyl-tRNA synthetase is an example of which class of enzymes?

A) Isomerase
B) Hydrolase
C) Ligase
D) Lyase
E) Transferase

Question 80

Synthesis of insulin in the beta-cell involves several proteolytic cleavages post-translationally. The products of these enzymatic cleavages which are secreted normally are

A) proinsulin and insulin
B) insulin and C-peptide
C) insulin and insulin-like growth factor
D) proinsulin, insulin, insulin-like growth factor and relaxin
E) insulin