Deck 27: Protein Metabolism

Question 1

Which step is NOT one of the five steps of protein synthesis?

A) termination and ribosome degradation
B) elongation of the peptide chain
C) initiation of peptide synthesis
D) activation of the amino acids
E) protein folding and posttranslational processing

Answer 1

A

Question 2

Formation of the ribosomal initiation complex for bacterial protein synthesis does NOT require:

A) EF-Tu.
B) formylmethionyl tRNA^fMet.
C) GTP.
D) initiation factor 2 (IF-2).
E) mRNA.

Answer 2

A

Question 3

In E. coli, aminoacyl-tRNA synthetases:

A) activate amino acids in 12 steps.
B) are amino acid-specific; there is at least one enzyme specific for each amino acid.
C) fall into two classes, each of which attaches amino acids to different ends of the tRNA.
D) have no proofreading activities.
E) require a tRNA, an amino acid, and GTP as substrates.

Answer 3

B

Question 4

Which statement is TRUE for protein synthesis in eukaryotes?

A) All proteins are initially synthesized with methionine at their C-terminus.
B) All proteins are initially synthesized with methionine at their N-terminus.
C) All proteins are initially synthesized with tryptophan at their C-terminus.
D) All proteins are initially synthesized with a multiple of 3 amino acids in their sequence.
E) None of the statements is true.

Question 5

Which statement describes a feature of the wobble hypothesis?

A) A naturally occurring tRNA exists in yeast that can read both arginine and lysine codons.
B) A tRNA can recognize only one codon.
C) Some tRNAs can recognize codons that specify two different amino acids if both are nonpolar.
D) The "wobble" occurs only in the first base of the anticodon.
E) The "wobble" occurs only in the third base of the anticodon.

Question 6

Bacterial ribosomes:

A) bind tightly to specific regions of DNA, forming polysomes.
B) contain at least one catalytic RNA molecule (ribozyme).
C) contain three species of RNA and five different proteins.
D) have specific, different binding sites for each of the 20 tRNAs.
E) require puromycin for normal function.

Question 7

In the "activation" of an amino acid for protein synthesis:

A) leucine can be attached to tRNA^Phe, by the aminoacyl-tRNA synthetase specific for leucine.
B) methionine is first formylated, then attached to a specific tRNA.
C) the amino acid is attached to the 5' end of the tRNA through a phosphodiester bond.
D) there is at least one specific activating enzyme and one specific tRNA for each amino acid.
E) two separate enzymes are required, one to form the aminoacyl adenylate, the other to attach the amino acid to the tRNA.

Question 8

Which statement is TRUE about the genetic code?

A) All codons recognized by a given tRNA encode different amino acids.
B) It is absolutely identical in all living things.
C) Several different codons may encode the same amino acid.
D) The base in the middle position of the tRNA anticodon sometimes permits "wobble" base pairing with two or three different codons.
E) The first position of the tRNA anticodon is always adenosine.

Question 9

In bacteria the elongation stage of protein synthesis does NOT involve:

A) aminoacyl-tRNAs.
B) EF-Tu.
C) GTP.
D) IF-2.
E) peptidyl transferase.

Question 10

The enzyme that attaches an amino acid to a tRNA (aminoacyl-tRNA synthetase):

A) always recognizes only one specific tRNA.
B) attaches a specific amino acid to any available tRNA species.
C) attaches the amino acid at the 5' end of the tRNA.
D) catalyzes formation of an ester bond.
E) splits ATP to ADP + P_i.

Question 11

Assuming that the average amino acid residue contributes 110 to the peptide molecular weight, what will be the minimum length of the mRNA encoding a protein of molecular weight 50,000?

A) 133 nucleotides
B) 460 nucleotides
C) 1,400 nucleotides
D) 5,000 nucleotides
E) A minimum length cannot be determined from the data given.

Question 12

Which statement about ribosomes is TRUE?

A) The large subunit contains rRNA molecules; the small subunit does not.
B) The RNA in ribosomes plays a structural, not catalytic, role.
C) There are about 25 ribosomes in an E. coli cell.
D) There are two major ribosomal subunits, each with multiple proteins.
E) Ribosomes are relatively small, with molecular weights less than 10,000.

Question 13

Which statement about bacterial mRNA is TRUE?

A) A ribosome usually initiates translation near the end of the mRNA that is synthesized last.
B) An mRNA is never degraded but is passed on to the daughter cells at cell division.
C) During polypeptide synthesis, ribosomes move along the mRNA in the direction 5' $\rightarrow$ 3'.
D) Ribosomes cannot initiate internally in a polycistronic transcript.
E) The codon signaling peptide termination is located in the mRNA near its 5' end.

Question 14

Aminoacyl-tRNA synthetases (amino acid activating enzymes):

A) "recognize" specific tRNA molecules and specific amino acids.
B) in conjunction with another enzyme attach the amino acid to the tRNA.
C) interact directly with free ribosomes.
D) occur in multiple forms for each amino acid.
E) require GTP to activate the amino acid.

Question 15

Which statement about aminoacyl-tRNA synthetases is FALSE?

A) Some of the enzymes have an editing/proofreading capability.
B) The enzyme attaches an amino acid to the 3' end of a tRNA.
C) The enzyme splits ATP to AMP + PP_i.
D) The enzyme will use any tRNA species but is highly specific for a given amino acid.
E) There is a different synthetase for every amino acid.

Question 16

Which statement about the elongation phase of protein synthesis is TRUE?

A) At least five high-energy phosphoryl groups are expended for each peptide bond formed.
B) During elongation, incoming aminoacylated tRNAs are first bound in the P site.
C) Elongation factor EF-Tu facilitates translocation.
D) Peptidyl transferase catalyzes the attack of the carboxyl group of the incoming amino acid on an ester linkage in the nascent polypeptide.
E) Peptidyl transferase is a ribozyme.

Question 17

Which statement is NOT true about RNA editing?

A) RNA editing occurs mostly in mitochondria and chloroplasts.
B) RNA editing requires guide RNAs that have sequences complementary to the edited mRNA.
C) Deamination of G is a common reaction in RNA editing.
D) Deamination of A is common reaction in RNA editing.
E) RNA editing allows for the synthesis of two different proteins from one gene.

Question 18

Which statement about tRNA molecules is FALSE?

A) A, C, G, and U are the only bases present in the molecule.
B) Although composed of a single strand of RNA, each molecule contains several short, double-helical regions.
C) Any given tRNA will accept only one specific amino acid.
D) The amino acid attachment is always to an A nucleotide at the 3' end of the molecule.
E) There is at least one tRNA for each of the 20 amino acids.

Question 19

Which statement about the tRNA that normally accepts phenylalanine is FALSE? (mRNA codons for phenylalanine are UUU and UUC.)

A) It interacts specifically with the Phe synthetase.
B) It will accept only the amino acid phenylalanine.
C) Its molecular weight is about 25,000.
D) Phenylalanine can be specifically attached to an -OH group at the 3' end.
E) The tRNA must contain the sequence UUU.

Question 20

Which statement is NOT true of tRNA molecules?

A) The 3'-terminal sequence is -CCA.
B) Their anticodons are complementary to the triplet codon in the mRNA.
C) They contain more than four different bases.
D) They contain several short regions of double helix.
E) With the right enzyme, any given tRNA molecule will accept any of the 20 amino acids.

Question 21

Which statement is TRUE regarding wobble pairs in translation?

A) The wobble position is the first position in the anticodon.
B) A in the anticodon can pair with C or U.
C) C and G in the anticodon can each pair with two nucleotides.
D) Inosine in the wobble position can pair with both purines.
E) G:U pairs are never found in the wobble position.

Question 22

Which compound is NOT utilized for protein degradation in eukaryotes?

A) ATP
B) ubiquitin ligases
C) deubiquitinases
D) lon protease
E) proteasome

Question 23

Approximately how many NTPs must be converted to NDPs to incorporate one amino acid into a protein?

A) zero
B) one
C) two
D) four
E) eight

Question 24

If you carry out peptide synthesis using an RNA with the sequence (AG)_N, what are the possible results?

A) PolyArginine only.
B) PolyLeucine and polySerine.
C) PolyLeucine only.
D) PolyArginine and polyGlutamate
E) PolySerine only.

Question 25

The pathway for polypeptides exported from E. coli includes the following steps, which occur in what order for CORRECT export?

Question 26

Which antibiotic does NOT function by interfering with the translational process?

A) chloramphenicol
B) cycloheximide
C) penicillin
D) puromycin
E) streptomycin

Question 27

Glycosylation of proteins inside the endoplasmic reticulum does NOT involve:

A) a His residue on the protein.
B) an Asn residue on the protein.
C) dolichol phosphate.
D) glucose.
E) N-acetylglucosamine.

Question 28

Posttranslational glycosylation of proteins is inhibited specifically by:

A) chloramphenicol.
B) cycloheximide.
C) puromycin.
D) streptomycin.
E) tunicamycin.

Question 29

If there is only one tRNA that can insert a glutamic acid residue (Glu), its anticodon sequence should be:

A) 5´-UUC-3´.
B) 5´-CUC-3´.
C) 5´-IUC-3´.
D) 5´-UUI-3´.
E) 5´-CUU-3´.

Question 30

Ubiquitin-mediated protein degradation is a complex process, and many of the signals remain unknown. One known signal involves recognition of amino acids in a processed protein that are either stabilizing (Ala, Gly, Met, Ser, etc.) or destabilizing (Arg, Asp, Leu, Lys, Phe, etc.) and are located at:

A) a helix-turn-helix motif in the protein.
B) a lysine-containing target sequence in the protein.
C) a zinc finger structure in the protein.
D) the amino-terminus of the protein.
E) the carboxy-terminus of the protein.

Question 31

The large structure consisting of a mRNA molecule being translated by multiple copies of the macromolecular complexes that carry out protein synthesis is called a:

A) lysosome.
B) polysome.
C) proteosome.
D) ribosome.
E) synthosome.

Question 32

Inosine is unable to form a wobble-pair with which nucleotides?

A) A only
B) C only
C) G only
D) U only
E) either A or G

Question 33

Which amino acids are coded for by a single codon?

A) methionine only
B) isoleucine only
C) methionine and isoleucine
D) methionine and tryptophan
E) methionine, isoleucine, and tryptophan

Question 34

Why does poly(G) NOT yield any peptide product when used in a peptide synthesis experiment?

A) because GGG does not code for an amino acid
B) because CCC is not a possible anticodon sequence
C) because poly(G) structures do not remain as single strands
D) because ribosomes cannot bind to the sequence "GGG"
E) None of these reasons explains why no peptide product is produced.

Question 35

What is the minimum number of tRNA molecules that could code for serine?

A) one
B) two
C) three
D) four
E) six

Question 36

Which enzyme, discovered by Stephen Ochoa, was used to help to determine codon composition based on varying concentrations of nucleotides in experiments?

A) RNA polymerase II
B) reverse transcriptase
C) RNA replicase.
D) polynucleotide phosphorylase
E) DNA polymerase I

Question 37

The signal sequences that direct proteins to the nucleus are:

A) always at the amino terminus of the targeted protein.
B) cleaved after the protein arrives in the nucleus.
C) glycosyl moieties containing mannose 6-phosphate residues.
D) not located at the ends of the peptide, but in its interior.
E) the same as those that direct certain proteins to lysosomes.

Question 38

It is possible to convert the Cys that is a part of Cys-tRNA^Cys to Ala by a catalytic reduction. If the resulting Ala-tRNA^Cys were added to a mixture of (1) ribosomes, (2) all the other tRNAs and amino acids, (3) all of the cofactors and enzymes needed to make protein in vitro, and (4) mRNA for hemoglobin, where in the newly synthesized hemoglobin would the Ala from Ala-tRNA^Cys be incorporated?

A) Nowhere; this is the equivalent of a nonsense mutation.
B) Wherever Ala normally occurs
C) Wherever Cys normally occurs
D) Wherever either Ala or Cys normally occurs
E) Wherever the dipeptide Ala-Cys normally occurs

Question 39

Which statement is TRUE about the sorting pathway for proteins destined for incorporation into lysosomes or the plasma membrane of eukaryotic cells?

A) Binding of SRP to the signal peptide and the ribosome temporarily accelerates protein synthesis.
B) The newly synthesized polypeptides include a signal peptide at their carboxyl termini.
C) The signal peptide is cleaved off inside the mitochondria by signal peptidase.
D) The SRP binds to the signal peptide soon after it appears outside the ribosome.
E) The signal sequence is added to the polypeptide in a posttranslational modification reaction.

Question 40

The sequence below is found within the protein-coding region of an mRNA. Which effect would you NOT expect to observe if the highlighted C residue were deaminated? …GCUCCGAUGCC…

A) no change to the protein coding sequence
B) the formation of a truncated protein
C) a serine to leucine substitution
D) None of these effects would be observed.
E) None of these effects is a potential consequence.

Question 41

If fMet-tRNA^fMet were bound by EF-Tu, it would be:

A) delivered to the ribosomal A site.
B) delivered to the ribosomal P site.
C) delivered to the ribosomal E site.
D) unable to bind to the ribosome at all.
E) degraded.

Question 42

The Shine-Dalgarno sequence:

A) is found downstream of the transcription initiation site in mRNA.
B) forms a parallel duplex with sequences in ribosomal RNA.
C) is important in eukaryotic gene translation.
D) is complementary to the initiator tRNA anticodon.
E) None of the answers is correct.

Question 43

Which bases are important in ensuring a tRNA is charged with the correct amino acid?

A) bases that are highly conserved between different tRNAs
B) bases that vary between different tRNAs
C) any modified bases in the tRNA
D) all bases found in the anticodon loop
E) All of the bases are equally important.

Question 44

If the nucleotides C and G are mixed together in a 1:1 ratio with polynucleotide phosphorylase in the Ochoa/Nirenberg experiments, which amino acids would NOT be incorporated into polypeptides?

A) Ala
B) Arg
C) Glu
D) Gly
E) Pro

Question 45

The reaction catalyzed by a tRNA synthetase:

A) consumes the equivalent of at least two phosphoanhydride bonds.
B) uses ATP to activate the carboxylate of the amino acid.
C) has as a final product an ester linkage between an adenosine and the amino acid.
D) All of the answers are correct.
E) None of the answers is correct.

Question 46

What was the primary conclusion of the Dintzis experiment?

A) that DNA replication is semiconservative
B) the determination of the genetic code for protein synthesis
C) that catalytic RNA is important in protein synthesis
D) the directionality of polypeptide synthesis
E) that ribosomes are ribozymes

Question 47

Which reaction in protein synthesis leads to formation of an ester bond in one of its products?

A) tRNA charging with amino acids
B) binding of aminoacyl-tRNA to the ribosome
C) reaction of the A-site acylated-tRNA with the P-site acylated-tRNA
D) the translocation step in protein synthesis
E) release of the final peptide product

Question 48

Which process is involved in generating the different forms of the apoB gene product in the liver and intestines?

A) alternative 5´ splice-site choice only
B) alternative 3´ splice-site choice only
C) deamination of cytosine
D) deamination of adenine
E) None of the answers is correct.

Question 49

Which statement is FALSE concerning translation of the apoB gene?

A) apoB is a single gene that is expressed in both liver and intestine.
B) The liver produces a longer protein product than the intestine.
C) In the intestine, cytidine deaminase converts C nucleotide into a U.
D) Guide RNA molecules mostly complementary to RNA to be edited serve as a template.
E) Edited mRNA for apoB creates a termination codon from one for glutamine.

Question 50

During protein translocation to the ER:

A) mRNA for ER-targeted protein is initially translated on ER-associated ribosomes.
B) emergence of the C-terminal signal sequence is bound by the ribonucleoprotein, SRP.
C) SRP binds to both the signal peptide and ribosome and halts translation.
D) SRP binds to SRP receptor and tethers the mRNA/ribosome to the nucleus.
E) the complex of SRP/SRP receptor/mRNA/ribosome migrates to the translocon, where signal peptidase cleavage facilitates SRP dissociation and translation continues.

Question 51

Which statement is NOT evidence supporting the idea that ribosomes are ribozymes?

A) rRNAs are highly conserved.
B) Experiments show that mutations in proteins cause resistance to antibiotics that inhibit protein synthesis.
C) Extraction of ribosomal proteins does not greatly affect peptidyltransferase activity.
D) Ribosomal RNA forms the structural core of the ribosome.
E) None of the statements is evidence supporting the idea.

Question 52

Which statement does NOT describe a general aspect of signal peptides?

A) They are often found at the N-terminus of secreted proteins.
B) They contain 10-15 hydrophobic amino acids.
C) They contain one or more negatively charged residues.
D) They tend to form an $\alpha$ -helical structure.
E) All of these are general aspects of signal pepides.

Question 53

Addition of O-linked glycosylations occurs predominantly in which cellular compartment?

A) the nucleus
B) the endoplasmic reticulum
C) the Golgi apparatus
D) lysosomes
E) endosomes

Question 54

Which process is NOT accompanied by the activity of pyrophosphatase in E. coli?

A) DNA replication
B) transcription
C) aminoacylation of tRNA
D) All of these are accompanied by the activity of pyrophosphatase.
E) None of these is accompanied by the activity of pyrophosphatase.

Question 55

Which statement is FALSE with respect to disruption of protein synthesis by puromycin?

A) The antibiotic puromycin resembles the aminoacyl end of a charged tRNA.
B) Puromycin binds to the ribosomal P site and causes premature dissociation of the peptide from the ribosome.
C) The amine group of puromycin acts as a nucleophile.
D) Formation of peptide-puromycin causes premature chain termination.
E) Puromycin becomes covalently attached to the C-terminal end of the peptide being synthesized.

Question 56

What signal is used to identify a protein for transport to the lysosome?

A) phosphorylation of N-acetylglucosamine residues in the ER
B) phosphorylation of glucose residues in the ER
C) phosphorylation of mannose residues in the ER
D) phosphorylation of glucose residues in the Golgi apparatus
E) phosphorylation of mannose residues in the Golgi apparatus

Question 57

Ile-tRNA synthetase:

A) has an acylation site that rejects amino acids that are smaller than the correct one.
B) has a hydrolytic site that destroys activated intermediates that are larger than the correct species.
C) has no proofreading ability.
D) is unable to incorporate valine or leucine into aminoacylated tRNA structures.
E) catalyzes aminoacylation of tRNA whereby the carboxyl group of an amino acid is joined to the 3´-OH of a tRNA.

Question 58

What is a distinguishing characteristic between Class I and Class II aminoacyl-tRNA synthetases?

A) Class I enzymes are ligases, while Class II enzymes are lyases.
B) Class I enzymes have proofreading, while Class II enzymes do not.
C) Class I enzymes bind to specific nucleotides in tRNA substrates, while Class II enzymes do not.
D) Class I enzymes transfer amino acids to the 2´ OH, while Class II enzymes transfer amino acids to the 3´ OH.
E) None of the answers is correct.

Question 59

Which statement is FALSE regarding the EF-G in prokaryotic translation?

A) EF-G is a nucleotide hydrolase.
B) EF-G is associated with the translocation step of translation.
C) EF-G is needed for initiation and elongation steps in synthesis.
D) EF-G is structurally similar to a tRNA/EF-TU complex.
E) None of the statements is false.

Question 60

If a glycosylated protein is purified from the ER, what would you expect to be TRUE about this protein?

A) The glycosyl groups will contain very little mannose.
B) The glycosylations are likely to be N-linked.
C) The protein will still contain a signal sequence.
D) The protein will be targeted to lysosomes.
E) The protein will be an integral membrane protein.

Question 61

You have isolated a fragment of viral DNA that totally encodes at least two proteins, 120 and 80 amino acids long. The DNA fragment is 400 base pairs long. (a) Why might you consider this unusual? (b) You sequence the two proteins and find no sequence homology. Propose a model to account for these findings.

Question 62

Describe the possible outcomes that could occur because of a single base change in an mRNA.

Question 63

In protein synthesis, 61 codons specify the 20 amino acids. Base pairing between the codon and the tRNA anticodon assures that the correct amino acid will be inserted into the nascent polypeptide chain. Why then does the cell require only 32 different tRNAs to recognize 61 different codons?

Question 64

A given mRNA sequence might be translated in any of three reading frames. Describe how prokaryotes and eukaryotes determine the correct reading frame.

Question 65

Which statement does NOT accurately compare ER signal sequences and nuclear localization sequences?

A) Nuclear localization sequences are not removed, while ER signal sequences usually are.
B) Nuclear localization sequences may be located anywhere, while signal sequences are usually found at the amino terminus.
C) Both nuclear localization sequences and signal sequences must contain multiple Asp and Glu residues.
D) Nuclear localization sequences and ER signal sequences are both sites for protein:protein interactions.
E) All these statements accurately describe these sequences.

Question 66

Number the following steps in the proper order with regard to protein synthesis.
___ Aminoacyl-tRNA binds to the A site.
___ Deacylated tRNA is released from ribosome.
___ Peptide bond formation shifts the growing peptide from the P to the A site.
___ The 50S subunit binds to the initiation complex of the 30S subunit and mRNA.

Question 67

The process of charging tRNAs with their cognate amino acids involves multiple proofreading steps to increase the overall fidelity. Briefly describe these steps.

Question 68

Describe two ways in which synthetic polynucleotides were used in solving the genetic code (you need not describe how the synthetic polynucleotides were made).

Question 69

Match the factor or enzyme at the right with the stage(s) of protein synthesis at which it acts. If a factor or enzyme participates in two stages of protein synthesis, indicate both of them.
___ Amino acid activation
(a) RF₁
___ Initiation
(b) EF-Tu
___ Elongation
(c) Aminoacyl-tRNA
___ Termination
(d) Shine-Dalgarno sequence

Question 70

Explain how insertions and deletions were used to provide evidence that the genetic code was a triplet code.

Question 71

Ubiquitin is added to proteins targeted for degradation by formation of a(n):

A) ester bond between the C-terminus of ubiquitin and a serine of the target protein.
B) thioester bond between the C-terminus of ubiquitin and a cysteine of the target protein.
C) amide bond between the C-terminus of ubiquitin and a lysine of the target protein.
D) ester bond between a glutamate of ubiquitin and a serine in the target protein.
E) thioester bond between a glutamate of ubiquitin and a cysteine in the target protein.

Question 72

Consider the following hypothetical short mRNA; what would be the sequence of the protein produced if this were translated in an E. coli cell?
5'-AUAGGAGGUUUGACCUAUGCCUCGUUUAUAGCC-3'

Question 73

The recognition of an amino acid by its cognate aminoacyl-tRNA synthetase is said to involve a "second genetic code." What is meant by this?

Question 74

Which statement is FALSE concerning ubiquitin?

A) The sequence of this protein is highly conserved in prokaryotes.
B) This protein is covalently added to proteins targeted for degradation.
C) This protein is small (<100 amino acids).
D) This protein contains lysine residues.
E) This protein interacts with the 19S regulatory particle in proteasomes.

Question 75

The following sequence of four amino acids occurred in the structure of a polypeptide found in a wild-type organism: Leu-Ser-Ile-Arg. Several mutants were isolated, each of which carried a single base pair change in the region of DNA that coded for this amino acid sequence. Their corresponding amino acid sequences are:
Mutant
1
MET-Ser-Ile-Arg
2
Leu-TRP-Ile-Arg
3
Leu-Ser-ARG-Arg
4
Leu-Ser-Ile-PRO
5
Leu-Ser-Ile-TRP
What was the nucleotide sequence of the region of mRNA that coded for the amino acid sequence in the wild-type organism? (Refer to Fig. 27-7)

Question 76

Indicate whether each of the following statements is true (T) or false (F).
___ Assembly of a complete ribosome onto an mRNA requires ATP hydrolysis.
___ Aminoacylation or "charging" of tRNA requires the formation of an aminoacyl-AMP intermediate.
___ Aminoacyl-tRNA binding to the A site of the ribosome requires the accessory factor EF-G and GTP hydrolysis.
___ Translocation of a growing polypeptide from the A to the P site on the ribosome requires EF-G and GTP hydrolysis.
___ Termination of translation requires release factors, but no NTP hydrolysis.

Question 77

The template strand of a segment of double-stranded DNA contains the sequence:
(5')-CTT TGA TAA GGA TAG CCC TTC-(3')
(a) What is the base sequence of the mRNA that can be transcribed from this strand? (b) What amino acid sequence could be coded by the mRNA base sequence in (a), using only the first reading frame starting at the 5' end? (Refer to Fig. 27-7) (c) Suppose the other (complementary) strand is used as a template for transcription. What is the amino acid sequence of the resulting peptide, again starting from the 5' end and using only the first reading frame?

Question 78

Briefly describe the role of the following components in bacterial protein synthesis.
(a) Initiation factor 2 (IF-2)
(b) 16S RNA
(c) Peptidyl transferase
(d) Release factors
(e) Elongation factor G (EF-G)
(f) N¹⁰-formyltetrahydrofolate
(g) ATP
(h) tRNA^fMet

Question 79

Indicate whether the following statements are true (T) or false (F).
___ A ribosome is the complex within which protein synthesis occurs.
___ Ribosomes contain many separate proteins.
___ Ribosomes contain many different RNAs.
___ The three ribosomal RNAs in a bacterial ribosome are distributed in three separate, large ribosomal subunits.
___ The catalytic machinery of the ribosome is protein-based.
___ There are four binding sites for aminoacyl-tRNAs on a ribosome.

Question 80

In 1961, Howard Dintzis carried out an experiment that defined the direction of polypeptide chain growth during protein synthesis in cells. The experiment involved the analysis of hemoglobin molecules that were being synthesized in reticulocytes in the presence of radioactive amino acids. Describe the analysis and how it demonstrated the direction of chain growth.