Question 1

What was the primary conclusion of the Dintzis experiment?

Accepted Answer

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 
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 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?

Accepted Answer

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. 
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 3

Indicate whether each of the following statements is true (T) or false (F).
___ Bacterial mRNA is broken down within a few minutes of its formation in E. coli.
___ Bacterial mRNA consists only of the bases that code for amino acids.
___ Polysomes do not necessarily contain mRNA.
___ Bacterial mRNA normally occurs as a double-stranded structure, with one strand containing codons, the other containing anticodons.
___ Bacterial mRNA can be translated while it is still being synthesized.

Accepted Answer

___ T: Bacterial mRNA is broken down wit

Question 4

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

Accepted Answer

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

Question 5

During protein translocation to the ER:

Accepted Answer

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. 
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 6

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

Accepted Answer

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. 
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 7

Which statement about bacterial mRNA is TRUE?

Accepted Answer

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. 
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 8

Which statement is TRUE about the genetic code?

Accepted Answer

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. 
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

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

Accepted Answer

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

Question 10

The Shine-Dalgarno sequence:

Accepted Answer

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. 
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 11

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?

Accepted Answer

In protein synthesis, the genetic code i

Question 12

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

Accepted Answer

Insertions and deletions in the genetic

Question 13

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.

Accepted Answer

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 
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

Question 14

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

Accepted Answer

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. 
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 15

In no more than three sentences, describe a nonsense suppressor tRNA and how it differs from a normal tRNA.

Accepted Answer

A nonsense suppressor tRNA is a speciali

Question 16

In E. coli, aminoacyl-tRNA synthetases:

Accepted Answer

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. 
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.

Question 17

The reaction catalyzed by a tRNA synthetase:

Accepted Answer

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. 
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 18

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?

Accepted Answer

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 
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 19

Following the synthesis of their polypeptide chain, many proteins require further posttranslational modifications before they attain their full biological activity or function. List and describe briefly at least four possible types of modification that can occur.

Accepted Answer

1. Phosphorylation: This is the addition

Exam 27: Protein Metabolism

What was the primary conclusion of the Dintzis experiment?

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?

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

During protein translocation to the ER:

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

Which statement about bacterial mRNA is TRUE?

Which statement is TRUE about the genetic code?

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

The Shine-Dalgarno sequence:

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?

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

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

In no more than three sentences, describe a nonsense suppressor tRNA and how it differs from a normal tRNA.

In E. coli, aminoacyl-tRNA synthetases:

The reaction catalyzed by a tRNA synthetase:

Following the synthesis of their polypeptide chain, many proteins require further posttranslational modifications before they attain their full biological activity or function. List and describe briefly at least four possible types of modification that can occur.

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

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