Question 1

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

Accepted Answer

When one or two nucleotides were added to or deleted from a gene,the resulting mRNA produced a protein with a different amino acid sequence after the deletion or insertion.When three nucleotides were added or deleted,the resulting protein had a normal sequence except for the insertion or deletion of a single amino acid residue.

Question 2

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:

Accepted Answer

A) 800. 
B) 5,000. 
C) 30,000. 
D) 80,000. 
E) An upper limit cannot be determined from the data given. 
A) 800. 
B) 5,000. 
C) 30,000. 
D) 80,000. 
E) An upper limit cannot be determined from the data given. C

Question 3

Bacterial ribosomes:

Accepted Answer

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. 
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

Question 4

The ribosome does not have a comparable protease proofreading function like the exonuclease activity found in DNA polymerase.What is the "technical difficulty" that perhaps prevented the easy evolution of such an activity?

Accepted Answer

There are several aspects on can conside

Question 5

Which of the following are features of the wobble hypothesis?

Accepted Answer

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. 
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

A new antibiotic was recently discovered that inhibits prokaryotic protein synthesis.  In the presence of the antibiotic, protein synthesis can be initiated, but only dipeptides that remain bound to the ribosome are formed.  What specific step of protein synthesis is likely to be blocked by this antibiotic?

Accepted Answer

The antibi

Question 7

Which of the following is/are true for

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 above 
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

Question 8

In the "activation" of an amino acid for

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 9

What are the stages in targeting of nuclear proteins,and why are the targeting sequences not removed upon arrival of the protein in the nucleus?

Accepted Answer

In the cytoplasm, where eukaryotic prote

Question 10

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

Accepted Answer

(1)When synthetic polymers of only one n

Question 11

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) IF-2 is a protein factor that, when

Question 12

Which of the following statements about tRNA molecules is false?

Accepted Answer

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) 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 13

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

Accepted Answer

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. 
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.

Question 14

Which of the following statements 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.

Question 15

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 16

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:
 
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, p. 1107.)

Accepted Answer

(5')C or (

Question 17

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

Accepted Answer

The most likely result is a single amino

Question 18

Polypeptide chain elongation in E.coli occurs by the cyclical repetition of three steps.What are these steps and what cellular components are necessary for each of them to occur?

Accepted Answer

The three steps are: (1)An aminoacyl-tRN

Question 19

Formation of the ribosomal initiation complex for bacterial

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 20

Which one of the following statements about the elongation phase of

Accepted Answer

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. 
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.

Exam 27: Protein Metabolism

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

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:

Bacterial ribosomes:

The ribosome does not have a comparable protease proofreading function like the exonuclease activity found in DNA polymerase.What is the "technical difficulty" that perhaps prevented the easy evolution of such an activity?

Which of the following are features of the wobble hypothesis?

Which of the following is/are true for

In the "activation" of an amino acid for

What are the stages in targeting of nuclear proteins,and why are the targeting sequences not removed upon arrival of the protein in the nucleus?

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

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 of the following statements about tRNA molecules is false?

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

Which of the following statements about aminoacyl-tRNA synthetases is false?

Aminoacyl-tRNA synthetases (amino acid activating enzymes):

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

Polypeptide chain elongation in E.coli occurs by the cyclical repetition of three steps.What are these steps and what cellular components are necessary for each of them to occur?

Formation of the ribosomal initiation complex for bacterial

Which one of the following statements about the elongation phase of

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

Recombinant Dna Technology

Lipids

Biological Membranes and Transport

Biosignaling

Principles of Bioenergetics

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

Integration and Hormonal Regulation of Mammalian Metabolism

Genes and Chromosomes

Dna Metabolism

Rna Metabolism

Regulation of Gene Expression

Filters

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) tRNAf^Met