Which one of the following statements about the elongation phase of protein synthesis is true?

31. Which of the following is not utilized for protein degradation in eukaryotes? A) ATP B) Ubiquitin ligases C) Deubiquitinases D) Lon protease E) Proteasome

D

14. 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 + Pi.

D

15. In the "activation" of an amino acid for protein synthesis: A) leucine can be attached to tRNAPhe, 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.

D

18. 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.

D

24. Approximately how many NTPs must be converted to NDPs to incorporate one amino acid into a protein? A) 0 B) 1 C) 2 D) 4 E) 8

D

29. 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.

D

3. Which of the following are features 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.

D

11. 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.

A

17. Formation of the ribosomal initiation complex for bacterial protein synthesis does not require: A) EF-Tu. B) formylmethionyl tRNAfMet. C) GTP. D) initiation factor 2 (IF-2). E) mRNA.

A

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.

A

6. Which of the following 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

A

8. Which of the following statements 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.

A

12. 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.

B

16. Which of the following is/are 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 above

B

21. 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.

B

22. 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.

B

1. A certain bacterial mRNA is known to represent only one gene and to contain about 800 nucleotides. If you assume that the average amino acid residue contributes 110 to the peptide molecular weight, the largest polypeptide that this mRNA could code for would have a molecular weight of about: A) 800. B) 5,000. C) 30,000. D) 80,000. E) An upper limit cannot be determined from the data given

C

2. 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.

C

20. Which of the following statements 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' 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.

C

23. It is possible to convert the Cys that is a part of Cys-tRNACys to Ala by a catalytic reduction. If the resulting Ala-tRNACys 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-tRNACys 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

C

25. Which one of the following antibiotics does not function by interfering with the translational process? A) Chloramphenicol B) Cycloheximide C) Penicillin D) Puromycin E) Streptomycin

C

4. Which one of the following 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.

C

5. Which one of the following 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.

C

13. Which of the following statements 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 + PPi. 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.

D

26. Which of the following 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.

D

30. The pathway for polypeptides exported from E. coli includes the following steps, which occur in what order for correct export? 1. A chaperone, SecA, binds to the polypeptide. 2. A chaperone, SecB, binds to the polypeptide. 3. ATP is hydrolyzed by Sec A. 4. SecA pushes 20 amino acids of the polypeptide into the translocation complex. A) 1, 2, 3, 4 B) 1, 2, 4, 3 C) 2, 1, 4, 3 D) 2, 3, 1, 4 E) 3, 1, 4, 2

D

32. 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

D

7. Which one of the following statements 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.

D

10. Which of the following 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

E

19. Which one of the following statements 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.

E

28. Posttranslational glycosylation of proteins is inhibited specifically by: A) chloramphenicol. B) cycloheximide. C) puromycin. D) streptomycin. E) tunicamycin.

E

9. Which of the following statements 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.

E