Question 1

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

Accepted Answer

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. 
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 2

Which statement is NOT true of tRNA molecules?

Accepted Answer

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. 
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 3

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

The targeting of nuclear proteins involv

Question 4

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

Accepted Answer

The process of charging tRNAs with their

Question 5

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

Accepted Answer

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. 
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 6

Glycosylation of proteins inside the endoplasmic reticulum does NOT involve:

Accepted Answer

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

Question 7

If you carried out the Nirenberg and Ochoa experiments (mixing different nucleotide proportions with polynucleotide phosphorylase and using this RNA to synthesize peptides) using a 2:1 mixture of GTP and CTP, what would you expect to find in terms of (a) amino acids incorporated and (b) their relative abundance?

Accepted Answer

(a) If you carried out the Nirenberg and

Question 8

Describe the role of ubiquitin in mediating intracellular protein breakdown.

Accepted Answer

Ubiquitin plays a crucial role in mediat

Question 9

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?

Accepted Answer

(a) The base sequence of the mRNA that c

Question 10

Ile-tRNA synthetase:

Accepted Answer

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. 
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 11

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

Accepted Answer

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. 
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 12

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.

Accepted Answer

(a) This situation is unusual because it

Question 13

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

Accepted Answer

In both prokaryotes and eukaryotes, the

Question 14

Name three GTP binding factors that function in bacterial protein translation, and describe their function.

Accepted Answer

Three GTP binding factors that function

Question 15

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.

Question 16

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?

Accepted Answer

The term "second genetic code" refers to

Question 17

The codon for Trp is UGG, while UGA is a stop codon. Briefly explain why it would NOT be possible to have the reverse (UGG = stop, UGA = Trp).

Accepted Answer

The genetic code, which is the set of ru

Question 18

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

Accepted Answer

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)  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

Question 19

Which statement about ribosomes is TRUE?

Accepted Answer

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. 
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 20

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 involved in polypeptide

Exam 27: Protein Metabolism

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

Which statement is NOT true of tRNA molecules?

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?

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

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

Glycosylation of proteins inside the endoplasmic reticulum does NOT involve:

Describe the role of ubiquitin in mediating intracellular protein breakdown.

Ile-tRNA synthetase:

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

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

Name three GTP binding factors that function in bacterial protein translation, and describe their function.

Bacterial ribosomes:

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?

The codon for Trp is UGG, while UGA is a stop codon. Briefly explain why it would NOT be possible to have the reverse (UGG = stop, UGA = Trp).

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

Which statement about ribosomes is TRUE?

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?

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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