Question 1

Which statement is TRUE for protein synthesis in eukaryotes?

Accepted Answer

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. 
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. B

Question 2

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:

Accepted Answer

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. 
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

Question 3

Describe what would happen to bacterial protein synthesis if EF-Tu could recognize tRNAfMet.

Accepted Answer

EF-Tu is an essential bacterial elongation factor involved in protein synthesis. It plays a critical role in the translation process by binding to aminoacyl-tRNA (charged tRNA) and escorting it to the A site of the ribosome during the elongation phase of protein synthesis. EF-Tu ensures the accuracy of protein synthesis by only binding to correctly charged tRNAs, which are tRNAs that have been attached to their corresponding amino acids by aminoacyl-tRNA synthetases.

The notation "tRNA^fMet" seems to be a hypothetical or non-standard representation of a tRNA molecule. In the context of this question, let's assume it refers to a tRNA molecule that is somehow modified or different from the normal tRNAs that EF-Tu would recognize. The "fMet" part suggests it is a tRNA charged with formylmethionine, the modified amino acid used to initiate protein synthesis in bacteria.

If EF-Tu could recognize this modified tRNA, several scenarios could unfold, depending on the nature of the modifications:

1. If the modifications do not affect the overall function of the tRNA and it is correctly charged with formylmethionine, then protein synthesis would likely proceed normally. The initiation complex would form as usual, with fMet-tRNA positioned at the start codon on the mRNA, and subsequent elongation would occur with EF-Tu bringing in the appropriate aminoacyl-tRNAs.

2. If the modifications to the tRNA cause it to mispair with codons or to be charged with the wrong amino acid, this could lead to the incorporation of incorrect amino acids into the growing polypeptide chain, resulting in faulty proteins. This could have detrimental effects on the cell, potentially leading to loss of function or even cell death if the errors are severe and widespread.

3. If the modifications prevent the tRNA from interacting properly with the ribosome or other translation factors, even if EF-Tu can bind to it, the initiation and elongation processes could be hindered or blocked. This would result in a decrease in protein synthesis efficiency or a complete halt, which could be harmful to the bacterial cell.

In summary, the ability of EF-Tu to recognize a modified tRNA would depend on the nature of the modifications and their impact on the tRNA's function. If the modified tRNA can still participate correctly in translation, protein synthesis may proceed normally. However, if the modifications lead to errors in codon recognition or amino acid charging, or if they interfere with the translation machinery, bacterial protein synthesis could be compromised, potentially leading to harmful cellular consequences.

Question 4

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) tRNAfMet

Accepted Answer

(a) Initiation Factor 2 (IF-2): IF-2 is

Question 5

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

Accepted Answer

To match the factors or enzymes with the

Question 6

Which statement is TRUE regarding wobble pairs in translation?

Accepted Answer

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. 
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 7

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

Accepted Answer

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. 
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 8

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

Accepted Answer

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

Question 9

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?

Accepted Answer

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

Question 10

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.

Accepted Answer

Here are the statements with the indicat

Question 11

Describe the sequence of events between the transcription of an mRNA for a secreted protein and the arrival of that protein in the lumen of the endoplasmic reticulum.

Accepted Answer

The sequence of events between the trans

Question 12

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

Accepted Answer

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. 
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 13

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

Accepted Answer

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 
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 14

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.

Accepted Answer

In Howard Dintzis' experiment in 1961, h

Question 15

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

Accepted Answer

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

Question 16

Aminoacyl-tRNA synthetases (amino acid activating enzymes):

Accepted Answer

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)  "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 17

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

Accepted Answer

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. 
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.

Question 18

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

Accepted Answer

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. 
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 19

Regarding translation in eukaryotes versus that in prokaryotes (bacteria), indicate whether each of the following statements is true (T) or false (F).
___ In eukaryotes, the 3' end of the mRNA is associated with the 5' end during initiation, whereas in prokaryotes, it is not.
___ In prokaryotes, it is initiated at an AUG near a Shine-Dalgarno sequence in the mRNA, whereas in eukaryotes, it is initiated at an AUG near the 3' end of the mRNA.
___ In prokaryotes, it is initiated with Met, whereas in eukaryotes, it is initiated with fMet.
___ In prokaryotes, translation and transcription are coupled, whereas in eukaryotes, they are not.

Accepted Answer

Regarding the statements about translati

Question 20

Which statement about aminoacyl-tRNA synthetases is FALSE?

Accepted Answer

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. 
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.

Exam 27: Protein Metabolism

Which statement is TRUE for protein synthesis in eukaryotes?

Describe what would happen to bacterial protein synthesis if EF-Tu could recognize tRNAfMet.

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) tRNAfMet

Which statement is TRUE regarding wobble pairs in translation?

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

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

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?

Describe the sequence of events between the transcription of an mRNA for a secreted protein and the arrival of that protein in the lumen of the endoplasmic reticulum.

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

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

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

Aminoacyl-tRNA synthetases (amino acid activating enzymes):

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

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

Which statement about aminoacyl-tRNA synthetases is FALSE?

The Foundations of Biochemistry

Water

Amino Acids, Peptides, and Proteins

The Three-Dimensional Structure of Proteins

Protein Function

Enzymes

Carbohydrates and Glycobiology

Nucleotides and Nucleic Acids

DNA-Based Information Technologies

Lipids

Biological Membranes and Transport

Biosignaling

Bioenergetics and Biochemical Reaction Types

Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway

Principles of Metabolic Regulation

The Citric Acid Cycle

Fatty Acid Catabolism

Amino Acid Oxidation and the Production of Urea

Oxidative Phosphorylation and Photophosphorylation

Carbohydrate Biosynthesis in Plants and Bacteria

Lipid Biosynthesis

Biosynthesis of Amino Acids, Nucleotides, and Related Molecules

Hormonal Regulation and Integration of Mammalian Metabolism

Genes and Chromosomes

DNA Metabolism

RNA Metabolism

Regulation of Gene Expression

Filters

Describe what would happen to bacterial protein synthesis if EF-Tu could recognize tRNA^fMet.

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

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

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