Biochemistry 4th Edition by Donald Voet – Test Bank

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Biochemistry 4th Edition by Donald Voet – Test Bank

Chapter 6: Proteins: Three-Dimensional Structure

 

Matching

 

For questions 1-10:

A) tertiary structure
B) keratin
C) molecular chaperones
D) hydropathy
E) cis
F) trans
G) sterically forbidden conformation
H) regular secondary structure
I) collagen
J) peptide  bond
K) ribonuclease A (RNase A)
L) alpha

 

 

  1. Repeating values of f and y make up predictable orientations of amino acid with a chain, this predictable orientation forms___________.

 

Ans:  H

Level of Difficulty:  Easy

Section 6.1.B

Learning objective: Secondary Structure

 

  1. The strength of _______ comes from close packing of glycine residues and the characteristics of hydroxyproline allowing formation of a left- handed helical conformation which combines with two other left handed structures to form a right-handed triplet helix.

 

Ans:  I

Level of Difficulty:  Easy

Section 6.1.C

Learning Objective: Secondary Structure

 

  1. The overall arrangement of the regular structural elements such as the α helix and the β sheet in the protein are considered the protein’s ______.

 

Ans:  A

Level of Difficulty:  Easy

Section 6.2.C

Learning Objective: Tertiary Structure

 

 

  1. A historical experiment exploring denaturation upon β- mercaptoethanol reduction of disulfide bonds and spontaneous renaturation upon dialysis to remove the β- mercaptoethanol was carried out using the protein ______. This experiment demonstrated the importance of disulfide bonds and amino acid sequence in folding of proteins.

 

Ans:  K

Level of Difficulty:  Easy

Section 6.4.B

Learning Objective: Protein Stability

 

  1. A rigid, planar structure between at least two amino acids consisting of about 40% double bond character is characteristic of a ______.

 

Ans:  J

Section 6.1.A

Level of Difficulty:  Easy

Learning Objective: Primary Structure

 

  1. The _____________ of an amino acid can be used to predict whether an amino acid side chain folds towards the inside or outside of a globular protein.

 

Ans:  D

Level of Difficulty:  Easy

Section 6.2.B

Learning Objective: Tertiary Structure

 

  1. ________ is a fibrous protein that contains a hydrophobic amino acid approximately every 4 residues which forms an α helix with one hydrophobic side.

 

Ans:  B

Level of Difficulty:  Easy

Section 6.1.C

Learning Objective: Secondary Structure

 

  1. In most peptide groups the ______ conformation is not sterically favored.

 

Ans:  EF

Level of Difficulty:  Easy

Section 6.1.A

Learning Objective: Secondary Structure

 

 

 

 

 

 

  1. In vivo protein folding is often is assisted by ______.

 

Ans:  C

Level of Difficulty:  Easy

Section 6.5.B

Learning Objective: Protein Folding

 

  1. In a ______, the f and y angles of the peptide backbone would orient atoms closer than their van der Waals distance.

 

Ans:  G

Level of Difficulty:  Moderate

Section 6.1.A

Learning Objective: Secondary Structure

 

 

Multiple Choice

 

  1. In a Ramachandran diagram, a larger area represents sterically allowed torsion angles of f and y that are allowed in _____ rather than in ______ because there is greater opportunity for separation of amino acid side chains.

 

  1. A) secondary structure…tertiary structure
  2. B) α helix…β sheet
  3. C) β sheet…α helix
  4. D) tertiary structure…secondary structure
  5. E) none of the above

 

Ans:  C

Level of Difficulty:  Difficult

Section 6.1.A and B

Learning Objective: Secondary Structure

 

  1. In a protein, the most conformationally restricted amino acid is ______; the least conformationally restricted is ______.

 

  1. A) Trp, Gly
  2. B) Met, Cys
  3. C) Pro, Gly
  4. D) Ile, Ala
  5. E) Ala, Pro

 

Ans:  C

Level of Difficulty: Moderate

Section 6.1.A

Learning Objective: Secondary Structure

 

  1. Which of the following has (have) both a favorable hydrogen bonding pattern and f and y values that fall within the allowed Ramachandran conformational regions?

 

  1. A) a helix
  2. B) collagen helix
  3. C) b sheet
  4. D) all of the above
  5. E) none of the above

 

Ans:  D

Level of Difficulty:  Moderate

Section 6.1.A, B, and C

Learning Objective: Secondary Structure

 

  1. Which one of these characteristics is not true for the a helix?

 

  1. A) There are 3.6 amino acids per turn.
  2. B) There is a requirement for glycine every third amino acid residue.
  3. C) A hydrogen bond forms between the carbonyl oxygen of the nth amino acid residue and the –       NH group of the (n + 4)th amino acid residue.
  4. D) Proline is typically not found in the a
  5. E) It is right-handed.

 

Ans:  B

Level of Difficulty:  Easy

Section 6.1.B

Learning Objective: Secondary Structure

 

  1. Which of these characteristics does not describe the b sheet?

 

  1. A) Amino acid side chains are located both above and below the sheet.
  2. B) b sheets have a pleated edge-on appearance.
  3. C) They can exist in either parallel or antiparallel configurations.
  4. D) The sheets contain as few as two and as many as 22 polypeptide chains.
  5. E) Parallel b sheets containing fewer than five chains are the most common.

 

Ans:  E

Level of Difficulty: Moderate

Section 6.1.B

Learning Objective: Secondary Structure

 

 

 

 

 

 

  1. Which statement below does not describe fibrous proteins?

 

  1. A) Domains have a globular fold.
  2. B) These proteins usually contain only one type of secondary structure.
  3. C) These proteins usually exhibit structural or protective characteristics.
  4. D) These proteins have usually elongated hydrophilic surfaces.
  5. E) These proteins are usually insoluble in water.

 

Ans:  A

Level of Difficulty: Moderate

Section 6.1.C

Learning Objective: Secondary Structure

 

  1. Which of the following changes would not alter the functional characteristics of α keratin?

 

  1. A) Increasing the number of residues per turn to 4.1 while maintaining the same amino acid
  2. B) Substitution of a hydrophilic amino acid for a hydrophobic amino acid at position a and d of the 7-residue pseudorepeat.
  3. C) Decreasing the number of cysteine amino acids within each protofilament.
  4. D) Changing the environment surrounding the protein to one that is more reductive.
  5. E) All of the above would alter the functional characteristics of keratin.

 

Ans:  E

Level of Difficulty:  Difficult

Section 6.1.C

Learning Objective: Secondary Structure

 

  1. Which of the following statements is true regarding collagen?

 

  1. A) The inability to hydroxylate proline results in the inability to synthesize collagen.
  2. B) The α helical structure is ideal for intertwining 3 filaments.
  3. C) Hydrogen bonds between the ─OH groups of Hyp residues stabilize the helix.
  4. D) The requirement for glycine every 3rd amino acid is essential for the triplet helix formation.
  5. E) On average, there is one proline for every hydroxyproline.

 

Ans:  D

Level of Difficulty:  Difficult

Section 6.1.C

Learning Objective: Secondary Structure

 

 

 

 

 

 

  1. Which of the following gives the best example of a nonrepetitive structure in a protein?

 

  1. A) a random sequence of 12 amino acids with high Pα values forming an α helix
  2. B) an amino acid sequence with the following pattern “…a-b-c-d-e-a-b-c-d-a-b-c-d…”
  3. C) a 13 residue α helix with a Gln at position n+12 which hydrogen bonds to a residue at position n+10
  4. D) All of the above statements describe nonrepetitive protein structures.
  5. E) None of the above describe nonrepetitive protein structures.

 

Ans:  C

Level of Difficulty:  Difficult

Section 6.1.D

Learning Objective: Secondary Structure

 

  1. Which of the following is true regarding crystalline proteins?

 

  1. A) Many crystallized enzyme proteins remain catalytically active.
  2. B) The diffractive pattern observed during X-ray exposure to the crystal can be used to calculate the electron density map of the crystalline protein.
  3. C) The larger region indicating electron density with in the electron density map, the more accurate the structure
  4. D) A and B are true.
  5. E) A, B, and C are true.

 

Ans:  D

Level of Difficulty: Moderate

Section 6.2.A

Learning Objective: Tertiary Structure

 

  1. In the absence of ascorbic acid, prolyl oxidase is unable to oxidize proline residues in collagen to hydroxyproline, resulting in:

 

  1. A) lathyrism
  2. B) prion diseases
  3. C) amyloid formation
  4. D) scurvy
  5. E) allysine

 

Ans: D

Level of Difficulty:  Easy

Section 6.5.C

Learning Objective: Protein Folding

 

 

 

 

  1. Of the following, which amino acid is most likely to be found in position 1 or 4 on α keratin?

 

  1. A) Phe
  2. B) Ala
  3. C) Lys
  4. D) Trp
  5. E) Pro

 

Ans: B

Level of Difficulty: Moderate

Section 6.2.B and 6.1.C

Learning Objective: Tertiary Structure and Secondary Structure

 

  1. Which of the following amino acids combinations have side chains with groups that have the greatest ability to stabilize the tertiary structure of a protein?

 

  1. A) Lys and Arg
  2. B) Cys and Glu
  3. C) Glu and Lys
  4. D) Gln and Glu
  5. E) Pro and Asp

 

Ans: C

Level of Difficulty:  Difficult

Section 6.4.A

Learning Objective: Protein Stability

 

  1. The low pH found in the gut can enhance the digestibility of dietary protein by causing ___.

 

  1. A) amide hydrolysis
  2. B) protein denaturation
  3. C) disulfide reduction
  4. D) prion formation
  5. E) cysteine oxidation

 

Ans: B

Level of Difficulty:  Moderate

Section 6.4.B

Learning Objective: Protein Stability

 

 

 

 

 

 

 

  1. Which of the following occurs first when folding a disordered polypeptide chain into a stable protein formation?

 

  1. A) formation of a low energy state
  2. B) association of ordered subunits
  3. C) aggregation of hydrophobic regions in the protein
  4. D) tertiary structure refinement
  5. E) formation of a low entropy state

 

Ans: C

Level of Difficulty:  Moderate

Section 6.5.A

Learning Objective: Protein Folding

 

  1. Imagine that a researcher treated a protein with a high concentration of a chaotropic agent. Which of the following is the most likely result of the treatment?

 

  1. Nonpolar portions of the protein become more soluble.
  2. The protein begins to denature ,

III.  The protein stability increases due to hydrophobic collapse,

 

  1. A) I, II, III
  2. B) I, II
  3. C) II, III
  4. D) I, III
  5. E) II

 

Ans: B

Level of Difficulty:  Difficult

Section 6.4.B and 6.5.A

Learning Objective: Protein Folding

 

  1. For b-sheets, the terms ‘parallel’ and ‘antiparalllel’ refer to ___________.

 

  1. A) the ‘direction’ of the associated peptide strands
  2. B) the orientation of the amide cross-links
  3. C) the quaternary structure of the protein
  4. D) the orientation of the hydrogen bonding
  5. D) the topology of the reverse turns

 

Ans: A

Level of Difficulty:  Easy

Section 6.1.B

Learning Objective: Secondary Structure

 

 

  1. In general molecular chaperone proteins function by
  2. A) mediating disulfide bond formation
  3. B) synthesizing new proteins when one is misfolded.
  4. C) preventing premature folding by binding hydrophobic regions of the protein.
  5. D) enhancing salt bridge formation.
  6. E) none of the above

 

Ans: C

Level of Difficulty:  Moderate

Section 6.5.B

Learning Objective: Protein Folding

 

  1. Conventional one dimensional NMR spectroscopy is not generally an effective tool for determination of protein structure because…

 

  1. Proteins (including small proteins) have a high number of hydrogen atoms.
  2. NMR requires a high quality protein crystal.

III. The NMR spectra exhibit high peak overlap.

 

  1. A) I and II
  2. B) II and III
  3. C) I and III
  4. D) I, II, and III
  5. E) III only

 

Ans: C

Level of Difficulty:  Moderate

Section 6.2.A

Learning Objective: Tertiary Structure

 

  1. When comparing similarities among multiple protein structures, which of the following is false?

 

  1. A) Proteins with the same function from a different species are likely to have similar motifs.
  2. B) Proteins with the same function from different species are likely to be more similar in sequence than in structure.
  3. C) An effective protein motif isl likely be observed in multiple proteins.
  4. D) Proteins with the same motifs are likely to perform similar functions.
  5. E) None of the above statements are false.

 

Ans: B

Level of Difficulty:  Difficult

Section 6.2.C

Learning Objective: Tertiary Structure

 

  1. The structure and sequence of a protein of unknown function was examined. Which of the following provides the best prediction of the protein’s function?

 

  1. A) the observation of several disordered α helical domains.
  2. B) the observation of multiple protein subunits.
  3. C) the observation of motif known as the Rossmann fold.
  4. D) the observation of a large number of random coil regions.
  5. E) All of the above offer excellent prediction of the protein’s function.

 

Ans: C

Level of Difficulty:  Difficult

Section 6.2.C

Learning Objective: Tertiary Structure

 

  1. The Protein Data Bank (PDB) is a database provides structural information about proteins that may be useful for which of the following?

 

  1. A researcher studying the changes in protein fold associated with prions.
  2. A researcher classifying structural elements by function.

III  A researcher designing a compound to bind tightly to a particular region in the protein.

 

  1. A) I only
  2. B) II only
  3. C) III only
  4. D) I, II
  5. E) I, II, II

 

Ans: E

Level of Difficulty:  Moderate

Section 6.2.E

Learning Objective: Tertiary Structure

 

  1. Noncovalent forces that stabilize protein structure include all of the following except __________.

 

  1. A) the hydrophobic effect
  2. B) salt bridges
  3. C) electrostatic interactions with metal ions
  4. D) hydrogen bonding
  5. E) disulfide bridges

 

Ans: E

Level of Difficulty:  Easy

Section 6.4.A

Learning Objective: Protein Stability

 

  1. The classic experiment demonstrating that reduced and denatured RNase A could refold into the native form demonstrates that _______.

 

  1. A) 1° structure can determine 3° structure
  2. B) denaturation does not disrupt protein 2° structure
  3. C) disulfide bonds do not stabilize folded proteins
  4. D) All of the above.
  5. E) None of the above

 

Ans: A

Level of Difficulty: Moderate

Section 6.4.B

Learning Objective: Protein Stability

 

  1. The first step in the folding of disordered polypeptides into ordered functional protein is the formation of ______.

 

  1. A) 1o structure
  2. B) 2° structure
  3. C) 3° structure
  4. D) 4° structure
  5. E) hydrogen bonds

 

Ans: B

Level of Difficulty: Easy

Section 6.5.A

Learning Objective: Protein Folding

 

  1. Evolutionary processes have
  2. A) increased the stability of 4° structures.
  3. B) decreased the number of subunits.
  4. C) increased similarity amount 1° structures.
  5. D) enhanced efficient folding pathways.
  6. E) all of the above

 

Ans: D

Level of Difficulty: Moderate

Section 6.5.A

Learning Objective: Protein Folding

 

 

 

 

 

 

 

  1. Chaperonins such as the GroEL/ES system

 

  1. A) function with thermophilic proteins only.
  2. B) are required at low pH.
  3. C) require ATP hydrolysis.
  4. D) in vitro
  5. E) function in a nonaqueous environment.

 

Ans: C

Level of Difficulty: Moderate

Section 6.5.B

Learning Objective: Protein Folding

 

  1. Protein diseases can be caused by which of the following

 

  1. A) mutations affecting the 1° structure.
  2. B) mutations affecting the 3° structure.
  3. C) changes in the post-synthetic processing of proteins.
  4. D) All of the above are potential causes.
  5. E) None of the above are potential causes.

 

Ans: D

Level of Difficulty: Difficult

Section 6.5.C

Learning Objective: Protein Folding

 

  1. Which of the following would be most stable based on the information you have learned about protein structure?

 

  1. A) a loop region with 8 amino acids
  2. B) a β sheet region made up of amino acids Val, Ile, Phe
  3. C) an α helix made up of Cys, Pro, and Phe
  4. D) a β hairpin with 12 amino acids
  5. E) All have equal stability.

 

Ans:  B

Level of Difficulty: Difficult

Section 6.1.D

Learning Objective: Secondary Structure

 

 

 

 

 

 

 

  1. The structure of hen egg white protein has been solved and the torsion angles j and y are shown for each residue in the table below.  What structure motif most likely forms as a result of this protein sequence?

 

Residue Number j y
31 -61 -44
32 -72 -29
33 -66 -65
34 -67 -23
35 -81 -51
Break Break Break
42 -30 142
43 -142 150
44 -154 121
45 -91 136
46 -110 174

 

 

 

 

 

 

 

 

 

 

 

 

 

  1. A) β strand connected to another β strand with a break (or loop/turn) in between
  2. B) α Helix connect to another α Helix with a break (or loop/turn) in between
  3. C) β strand connected to another β strand with a alpha helix in between
  4. D) α Helix connected to a β strand with a break (or loop/turn) in between
  5. E) None of the above are correct.

 

Ans:  D

Level of Difficulty: Moderate

Section 6.1.A

Learning Objective: Secondary Structure

 

  1. Hydrogen bonds and maximum separation of amino acid side chains make the _____very stable and energetically ______________.

 

  1. A) α helix and β sheet, favorable
  2. B) α helix, unfavorable
  3. C) β sheet, unfavorable
  4. D) α helix, favorable
  5. E) β sheet, favorable

 

Ans:  A

Level of Difficulty: Moderate

Section 6.1.B

Learning Objective: Secondary Structure

 

 

 

 

 

  1. A chaperonin
  2. A) helps fold some proteins in their lowest energy state.
  3. B) is required for all proteins to fold properly.
  4. C) mediates the unfolding of proteins.
  5. D) is required for protein denaturation.
  6. E) counteracts the laws of thermodynamics.

 

Ans:  A

Level of Difficulty: Moderate

Section 6.5.B

Learning Objective: Protein Folding

 

  1. A helix has hydrogen bonds between the carbonyl group from residue “n” and the amino group of residue “n+6,” which of the following is TRUE?

 

  1. A) It has 3.6 residues per turn.
  2. B) It is a random coil, not a helix.
  3. C) It is an α helix.
  4. D) It has more residues per turn than an α helix.
  5. E) It has fewer residues per turn than an α helix.

 

Ans:  D

Level of Difficulty: Difficult

Section 6.1.B

Learning Objective: Secondary Structure

 

  1. Which of the following contribute to the minimization of energy that occurs with protein folding?

 

  1. A) orientating amino acid groups to maximize hydrogen bonding
  2. B) folding hydrophobic groups towards the exterior of the protein
  3. C) burying polar groups towards the interior of the protein
  4. D) extensive cavity formation
  5. E) all of the above

 

Ans:  A

Level of Difficulty: Moderate

Section 6.5.A

Learning Objective: Protein Folding

 

 

 

 

 

 

 

  1. Which of the following best describes the cause of Creutzfeld-Jakob Disease (a disease which human can develop with symptoms similar to those of mad cow disease)?

 

  1. A) aggregation of a misfolded protein.
  2. B) aggregation of random coil regions on a protein.
  3. C) ingestion of ammonium salts.
  4. D) the serious side effects of experimental treatment with Quinacrine E) All are potential causes Creutzfeld-Jakob disease.

 

Ans:  A

Level of Difficulty: Difficult

Section 6.5.C

Learning Objective: Protein Folding

  1. Which of the following lines in the figure at right indicates a b hairpin structure?

 

  1. A) A, C, D
  2. B) B and C
  3. C) A only
  4. D) A, B, and D
  5. E) C only

 

Ans:  D

Level of Difficulty: Easy

Section 6.1.C

Learning Objective: Secondary Structure

 

  1. Proteins can denature due to a change in

 

  1. A)
  2. B)
  3. C) ionic strength.
  4. D) all of the above
  5. E) none of the above

 

Ans:  D

Level of Difficulty: Easy

Section 6.4.A-C

Learning Objective: Protein Stability

 

 

 

 

 

 

  1. Examine the three sequences below for collagen-like proteins. If hydrogen bonding were the most important feature in determining strength in fibrous proteins, which of the following sequences likely has the highest melting temperature and why? (Note: Flp = fluoroproline; Hyp = hydroxyproline)

 

  1. Pro-Hyp-Gly-Pro-Hyp-Gly-Pro-Hyp-Gly
  2. Pro-Flp-Gly-Pro-Flp-Gly-Pro-Flp-Gly

III. Gly-Pro-Thr-Gly-Pro-Thr-Gly-Pro-Thr

 

  1. A) “1” because Hyp has OH groups
  2. B) “1” because the electronegativity of oxygen is greater
  3. C) “2” because the electronegativity of proline is greater
  4. D) “2” because the electronegativity of the –OH group increases hydrogen bond strength
  5. E) “3” because Thr is a small amino acid which allows close packing

 

Ans:  A

Level of Difficulty:  Difficult

Section 6.1.C and 6.4.A-C

Learning Objective: Protein Stability and Secondary Structure

 

  1. Based on what you know about fibrous protein structure and sequence, what type of fibrous protein is this sequence most likely to from (You can assume that the protein is longer than what is shown and is repeating as shown, also note the polarity of each amino acid.)?

 

Val – Cys – Lys – Val –  Cys – Ala – Cys – Val – Cys – Lys – Val –  Cys – Ala – Cys

 

  1. A) a keratin
  2. B) β keratin
  3. C) collagen
  4. D) pleated collagen
  5. E) This sequence cannot be from any of the structural proteins.

 

Ans:  A

Level of Difficulty: Difficult

Section 6.1.C

Learning Objective: Secondary Structure

 

 

 

 

 

 

 

 

 

 

  1. Which of the following structural proteins has the greatest elasticity?

 

  1. A) akeratin
  2. B) β ketatin
  3. C) collagen
  4. D) pleated collagen
  5. E) A and B are equal

 

Ans:  D

Level of Difficulty:  Difficult

Section 6.1.C

Learning Objective: Secondary Structure

 

  1. Noncovalent interactions account for the strength of which of the following structural proteins?

 

  1. A) a keratin
  2. B) collagen
  3. C) pleated collagen
  4. D) A and B
  5. E) B and C

 

Ans:  B

Level of Difficulty:  Moderate

Section 6.1.C

Learning Objective: Secondary Structure

 

  1. Examine the three sequences below for collagen-like proteins and their melting temperatures (Tm). (Note: Flp = fluoroproline; Hyp = hydroxyproline)  Based on this data, what is the most important feature in determining the strength of the collagen protein?

 

1)  …-Pro-Hyp-Gly-Pro-Hyp-Gly-Pro-Hyp-Gly-…   Tm=60oC

2)  …-Pro-Flp-Gly-Pro-Flp-Gly-Pro-Flp-Gly-…        Tm=78oC

3)  …-Gly-Pro-Thr-Gly-Pro-Thr-Gly-Pro-Thr-…       Tm=30oC

 

  1. A) hydrogen bonding
  2. B) inductive effect
  3. C) electrostatic effect
  4. D) electrostatic and Inductive effect are equal
  5. E) hydrogen bonding and inductive effect are equal

 

Ans:  B

Level of Difficulty: Difficult

Section 6.1.C, Chapter Supplement: Case 6 (Note to instructor: the text does not use the term inductive, the case does – if you have not assigned the case, you may want to consider whether your students should be expected to know the term inductive.)

Learning Objective: Secondary Structure; Chapter Supplement: Case 6

 

  1. When considering fibrous proteins, which of the following statements is TRUE?

 

  1. A) Noncovalent interactions contribute to the strength of all of these proteins.
  2. B) All of them consist of a helix structure.
  3. C) All of them require vitamin C.
  4. D) Decrease in amounts of any of them cause scurvy.
  5. E) All of these are true of fibrous proteins.

 

Ans:  A

Level of Difficulty: Easy

Section 6.1.C

Learning Objective: Secondary Structure

 

  1. In a Ramachandran diagram the region representing the angles of f and y that correspond to those commonly made by an amino acid that favors a left-handed a helix are different from those angles commonly made by an amino acid that favors right-handed a helix formation.  Which of the following statements provides a plausible explanation for this difference?

 

  1. A) Groups which would normally undergo high steric hindrance in the right-handed arrangement are separated maximally in the left-handed arrangement.
  2. B) Left-handed helices have smaller pitch than right-handed helices.
  3. C) The peptide backbone can coil tighter in the left-handed helices than in the right-handed
  4. D) Left-handed helices exhibit cyclic symmetry, while righthanded helices are asymmetric.
  5. E) All of the above are plausible explanations.

 

Ans:  A

Level of Difficulty: Difficult

Section 6.1.A

Learning Objective: Secondary Structure

 

  1. Which of the characteristics of collagen structure listed below contrubute to the tensi

le strength of collagen?

 

  1. Collagen is made up of a triplet helix where 3 left-handed helices twist together in a right handed sense.
  2. Collagen includes at repeating sequence of amino acids with glycine every 3 amino acids in a helix with about 3 amino acids per turn.

III. The three left-handed helices are staggered to allow close packing between glycine    residues and rigidity from the bulky and inflexible proline/hydroxyproline.

 

  1. A) I
  2. B) I and II
  3. C) I, II, and III
  4. D) II and III
  5. E) I and III

 

Ans:  C

Level of Difficulty: Difficult

Section 6.1.C

Learning Objective: Secondary Structure

 

  1. Native protein purifications often require multiple reaction steps in order to purify the protein of interest from other proteins. One method used for protein separation in purification procedures is a change from water to an organic solvent.  Which of the following would be accomplished by this solvent change?

 

  1. A) Proteins with hydrophobic groups on the interior would maintain their native state.
  2. B) Proteins with hydrophilic groups on the exterior would denature and likely precipitate.
  3. C) Proteins with exposed hydrophobic groups would maintain their structure and remain in
  4. D) Both A and B would occur.
  5. E) Both B and C would occur.

 

Ans:  E

Level of Difficulty: Difficult

Section 6.4.A

Learning Objective: Protein Stability

 

 

 

  1. When solving a protein structure using X-ray crystallography, the crystallographer generates a 3-D grid called an electron density map based on the observed diffraction pattern. The higher the resolution, the more detailed the electron density map and therefore the easier it is to identify what atoms (and therefore what amino acids) are in a given position. Based on the three choices below, in which of the following groups could the two of amino acids be the easiest to differentiate regardless of resolution?

 

  1. Leucine vs. Isoleucine
  2. Phenylalanine vs. Alanine

III.  Glutamate vs. Glutamic acid

 

  1. A) Those in both groups I and II could be differentiated
  2. B) Those in both groups I and III could be differentiated
  3. C) Only those in group II could be differentiated
  4. D) Only those in group III could be differentiated
  5. E) Only those in groupI could be differentiated

 

Ans:  C

Level of Difficulty: Difficult

Section 6.2.A

Learning Objective: Tertiary Structure

 

  1. Protein dynamics is a field of study that examines the movements with in a protein. Which type of protein structure determination would be most useful to study this type of change?

 

  1. A) X-ray crystallography
  2. B) Nuclear Magnetic Resonance (NMR)
  3. C) X-ray absorption spectroscopy
  4. D) A and B
  5. E) B and C

 

Ans:  B

Level of Difficulty: Difficult

Section 6.2.A

Learning Objective: Tertiary Structure

 

 

  1. What observation about protein refolding or renaturation helped to solidify the connection between primary amino acid sequence and 3-D structure?

 

  1. A) Spontaneous refolding of proteins into their native state under physiologic conditions.
  2. B) Assisted refolding of proteins into their native state under laboratory conditions.
  3. C) Identification of thermostable proteins than maintain their native state in adverse
  4. D) A and B
  5. E) B and C

 

Ans:  A

Level of Difficulty:  Moderate

Section 6.2.A

Learning Objective: Protein Structure

 

  1. Molecular chaperones bind to unfolded or partially folded polypeptide chains in order to accomplish which of the following?

 

  1. A) ensure that improper aggregation of hydrophobic segments does not occur
  2. B) engulf the protein in order to ensure that the protein is not damaged by heat denaturation
  3. C) facilitate native folding by exposing hydrophobic segments of the protein as it is synthesized
  4. D) facilitate aggregation of multiple subunits of a protein during synthesis
  5. E) All of the above are accomplished by molecular chaperones.

 

Ans:  A

Level of Difficulty:  Moderate

Section 6.4.B

Learning Objective: Protein Folding

 

Chapter 7: Protein Function Part I: Myoglobin and Hemoglobin

 

 

Matching

 

A)  positively cooperative
B)  cyanosis
C)  His E7
D)  decrease
E)  R
F)  hydrogen bonds
G)  increase
H)  symmetry
I)  His F8
J)  ion pairs
K)  T
L)  hemolytic anemia
M  sequencial

 

 

  1. When oxygen binds to heme, the oxygen forms a hydrogen bond with ______.

 

Ans:  C

Level of Difficulty:  Moderate

Section:  7.1.A

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. In the ______ state of hemoglobin, the iron ion is out of the plane of the porphyrin ring.

 

Ans:  K

Level of Difficulty:  Easy

Section:  7.1.B

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. The conversion of hemoglobin from the T to the R state requires breaking of ______ involving C-terminal residues.

 

Ans:  J

Level of Difficulty:  Easy

Section:  7.1.B

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

  1. Hemoglobin’s subunits bind oxygen in a ______ manner.

 

Ans:  A

Level of Difficulty:  Easy

Section:  7.1.C

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. An increase in pCO2 causes hemoglobin’s affinity for oxygen to ______.

 

Ans:  D

Level of Difficulty:  Easy

Section:  7.1.D

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. The absence of 2,3-BPG causes hemoglobin’s affinity for oxygen to______.

 

Ans:  G

Level of Difficulty:  Easy

Section:  7.1.D

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. The ______ model of allosterism requires subunits to change conformation simultaneously.

 

Ans:  H

Level of Difficulty:  Easy

Section:  7.1.D

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. Sickle cell hemoglobin does not form fibers in the ______ form.

 

Ans:  E

Level of Difficulty:  Easy

Section:  7.1.E

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

  1. When unstable hemoglobin is degraded; degradation products often cause cell lysis, leading to a condition called ______.

 

Ans:  L

Level of Difficulty:  Moderate

Section:  7.1.E

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. Mutations that favor the oxidation of the heme iron(II) to iron(III) can cause ______.

 

Ans:  B

Level of Difficulty:  Moderate

Section:  7.1.E

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

Multiple Choice

 

 

  1. Which of the following is not a ligand to the porphyrin ring Fe(II) ion in oxymyoglobin?
  2. A) His E7
  3. B) His F8
  4. C) Nitrogen atoms in the porphyrin ring
  5. D) Oxygen
  6. E) all are ligands

 

Ans:  A

Level of Difficulty:  Moderate

Section:  7.1.A

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. Which gas does not bind to the porphyrin ring Fe(II) ion in myoglobin?
  2. A) NO
  3. B) CO
  4. C) CO2
  5. D) O2
  6. E) H2S

 

Ans:  C

Level of Difficulty:  Easy

Section:  7.1.A

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. Which of the following statements does not apply to the K value in the equation for the oxygen binding curve of myoglobin?
  2. A) It is numerically equal to p50.
  3. B) It is defined as that oxygen partial pressure at which half of the oxygen binding sites are occupied.
  4. C) It is a measure of the affinity of myoglobin for oxygen.
  5. D) If Y > K, then myoglobin is less than 50% saturated with oxygen.
  6. E) It is the value of pO2 at which Y = 0.5.

 

Ans:  D

Level of Difficulty:  Easy

Section:  7.1.A

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

  1. Myoglobin’s secondary structure is primarily composed of ______________.
  2. A) parallel b-sheets
  3. B) antiparallel b-sheets
  4. C) a-helices
  5. D) W-loops
  6. E) polyproline helices

 

Ans:  C

Level of Difficulty:  Easy

Section:  7.1.A

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. Myoglobin’s primary physiological role is to facilitate oxygen ________.
  2. A) storage
  3. B) metabolism
  4. C) binding
  5. D) reduction
  6. E) diffusion

 

Ans:  E

Level of Difficulty:  Easy

Section:  7.1.A

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. If the gene for myoglobin is “knocked out” in mice, the mice:
  2. A) have larger lungs.
  3. B) respire extremely rapidly.
  4. C) have dark brown muscle tissue.
  5. D) appear normal, with lighter colored muscle tissue.
  6. E) have their growth stunted.

 

Ans:  D

Level of Difficulty:  Moderate

Section:  7.1.A

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

  1. Carbon monoxide binds to heme:
  2. A) with a higher affinity than oxygen.
  3. B) resulting in the oxidation of the Fe(II) to Fe(III)
  4. C) in a manner that displaces carbon dioxide, causing CO2
  5. D) from the side opposite oxygen, resulting in a brown colored heme.
  6. E) with a lower affinity than oxygen.

 

Ans:  A

Level of Difficulty:  Easy

Section:  7.1.A

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. Myoglobin and a single chain of hemoglobin have similar ______ structures.
  2. A) primary
  3. B) secondary
  4. C) tertiary
  5. D) quaternary
  6. E) none of the above

 

Ans:  C

Level of Difficulty:  Easy

Section:  7.1.B

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. The primary structure of mammalian hemoglobin, an a2b2 tetramer, is approximately _____ identical to myoglobin.
  2. A) 2%
  3. B) 18%
  4. C) 50%
  5. D) 78%
  6. E) 98%

 

Ans:  B

Level of Difficulty:  Moderate

Section:  7.1.B

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

  1. Hemoglobin is a heterotetramer. How many protomers are present in hemoglobin?
  2. A) 0
  3. B) 1
  4. C) 2
  5. D) 3
  6. E) 4

 

Ans:  C

Level of Difficulty:  Easy

Section:  7.1.B

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. What is the type of symmetry that relates the protomers in hemoglobin with respect to each other?
  2. A) C2
  3. B) C4
  4. C) D2
  5. D) D4
  6. E) Tetrahedral symmetry

 

Ans:  A

Level of Difficulty:  Easy

Section:  7.1.B

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. Hemerythrin and hemocyanin are:
  2. A) human mutant hemoglobins with decreased oxygen affinity.
  3. B) hemoglobin variants that are found in animals at high altitude.
  4. C) synthetic derivatives of hemoglobin’s heme group used in artificial blood substitutes.
  5. D) oxygen transport proteins found in invertebrates.
  6. E) tetrameric hemoglobin derivatives containing only a-chains (a4 tetramers).

 

Ans:  D

Level of Difficulty:  Easy

Section:  7.1.B

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

  1. Max Perutz’s investigation of the structure of hemoglobin primarily utilized_____.
  2. A) X-ray crystallography
  3. B) NMR spectroscopy
  4. C) genomics
  5. D) mass spectrometry
  6. E) genetic engineering

 

Ans:  A

Level of Difficulty:  Easy

Section:  7.1.B

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. The oxygen binding by hemocyanins is mediated by
  2. A) an iron ion
  3. B) a pair of iron ions
  4. C) a heme group
  5. D) a copper atom
  6. E) a pair of copper atoms

 

Ans:  E

Level of Difficulty:  Difficult

Section:  7.1.B

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. When the partial pressure of O2 in venous blood is 30 torr, the saturation of myoglobin with O2 is ______ while the saturation of hemoglobin with O2 is ______.
  2. A) 55, 0.91
  3. B) 91, 0.55
  4. C) 8 torr, 26 torr
  5. D) 91, 0.97
  6. E) none of the above

 

Ans:  B

Level of Difficulty:  Difficult

Section:  7.1.C

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

  1. Hemoglobin’s p50 value is about ______ as great as myoglobin’s p50 value.
  2. A) one-tenth
  3. B) half
  4. C) twice
  5. D) ten times
  6. E) twenty times

 

Ans:  D

Level of Difficulty:  Moderate

Section:  7.1.C

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. The value of n, the Hill constant (coefficient), for hemoglobin is about ______ as great as the value for myoglobin.
  2. A) half
  3. B) twice
  4. C) three times
  5. D) five times
  6. E) ten times

 

Ans:  C

Level of Difficulty:  Moderate

Section:  7.1.C

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. Consider a hypothetical hemoglobin-like molecule with a Hill coefficient (constant) of 1 and the same p50 value as normal hemoglobin. Choose the statement below that best describes the two proteins.
  2. A) There is a cooperative interaction between oxygen-binding sites in both the hypothetical and normal hemoglobins.
  3. B) The hypothetical hemoglobin has a greater oxygen affinity than normal hemoglobin.
  4. C) The oxygen binding curve for the hypothetical hemoglobin is hyperbolic, and the curve for normal hemoglobin is sigmoidal.
  5. D) The two hemoglobins would be able to deliver about the same amount of oxygen to the tissues.
  6. E) At pO2 less than p50, normal hemoglobin has a greater YO2

 

Ans:  C

Level of Difficulty:  Moderate

Section:  7.1.C

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

  1. The Hill plot shows that the fourth oxygen binds to hemoglobin with a ______-fold greater affinity than the first.
  2. A) 2
  3. B) 5
  4. C) 10
  5. D) 20
  6. E) 100

 

Ans:  E

Level of Difficulty:  Moderate

Section:  7.1.D

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. While the binding of O2 to myoglobin as a function of pO2 is described by a simple __________ curve, the binding to hemoglobin is described by a more complex ______ curve.
  2. A) sigmoidal; hyperbolic
  3. B) hyperbolic; sigmoidal
  4. C) exponential; hyperbolic
  5. D) sigmoidal; bell-shaped
  6. E) hyperbolic; concave

 

Ans:  B

Level of Difficulty:  Easy

Section:  7.1.D

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. The Bohr effect refers to
  2. A) the decrease in affinity of Hb for O2 when the pH goes down
  3. B) the decrease in affinity of Hb for O2 when the pH goes up
  4. C) the increase in the affinity of Hb for O2 when the O2 concentration goes up
  5. D) the decrease in affinity of Hb for O2 when the BPG concentration goes up
  6. E) the decrease in affinity of Hb for O2 when the BPG concentration goes down

 

Ans:  A

Level of Difficulty:  Easy

Section:  7.1.C

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

  1. Which of the following increases the affinity of hemoglobin for O2?
  2. A) an increase in BPG concentration
  3. B) the formation of N-terminal carbamates
  4. C) an increase in pH
  5. D) a decrease in pH
  6. E) an increase in CO2 concentration

 

Ans:  C

Level of Difficulty:  Moderate

Section:  7.1.D

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. The most rapid way that erythrocytes adapt to high altitudes is
  2. A) by producing genetically altered hemoglobins that have higher O2-binding affinities.
  3. B) by adopting the symmetry model of allosterism.
  4. C) by increasing the concentration of hemoglobin.
  5. D) by relying upon the simpler protein myoglobin.
  6. E) by increasing the intracellular concentration of BPG.

 

Ans:  E

Level of Difficulty:  Easy

Section:  7.1.D

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. The rearrangement of T state hemoglobin to the R state
  2. A) occurs in each protein subunit independently when its heme binds oxygen.
  3. B) requires the binding of at least three oxygen molecules.
  4. C) increases the ion pairing interactions of the C-terminal amino acids.
  5. D) involves the movement of the Fe(II) into the heme plane.
  6. E) opens a central cavity for BPG binding.

 

Ans:  D

Level of Difficulty:  Moderate

Section:  7.1.D

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

  1. Which of the following statements about the symmetry model of allosterism is not true?
  2. A) the protein is an oligomer of symmetrically (or pseudosymmetrically) related subunits.
  3. B) the oligomer can exist in two conformational states, which are in equilibrium.
  4. C) the ligand can bind to a subunit in either conformation.
  5. D) the molecular symmetry of the protein is conserved during the conformational change.
  6. E) none of the above.

 

Ans:  E

Level of Difficulty:  Moderate

Section:  7.1.D

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. BPG stands for
  2. A)
  3. B)
  4. C)
  5. D)
  6. E)

 

Ans:  C

Level of Difficulty:  Easy

Section:  7.1.D

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. Why is the decreased affinity of fetal hemoglobin for BPG advantageous?
  2. A) With fewer BPG molecules bound there are more heme residues available for O2
  3. B) Decreased BPG binding biases the fetal hemoglobin toward the R state.
  4. C) More free BPG is available to bind to adult hemoglobin, resulting in a shift to the R state.
  5. D) BPG is available to bind to fetal myoglobin, helping to release O2 in fetal muscle tissue.
  6. E) none of the above

 

Ans:  B

Level of Difficulty:  Difficult

Section:  7.1.D

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

  1. The reaction of carbonic anhydrase catalyzes
  2. A) the formation of carbamates with the concomitant release of protons.
  3. B) the hydration of bicarbonate, resulting in the formation of carbonic acid.
  4. C) the reduction of carbon dioxide with the concomitant consumption of protons.
  5. D) the hydration of carbon dioxide, forming bicarbonate and protons.
  6. E) the hydrolysis of carbamates with the concomitant consumption of protons.

 

Ans:  D

Level of Difficulty:  Easy

Section:  7.1.D

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. During the T to R conformational shift, Fe(II) drags the F-helix via a bond to the side chain of ________.
  2. A) Leu F7
  3. B) Leu F4
  4. C) His F8
  5. D) Leu FG3
  6. E) Val FG5

 

Ans:  C

Level of Difficulty:  Easy

Section:  7.1.D

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. Some abnormal hemoglobins have Hill coefficients that are ______ that of normal hemoglobin, indicating that their ability to bind oxygen cooperatively has been compromised.
  2. A) less than
  3. B) greater than
  4. C) much greater than
  5. D) about equal to
  6. E) The correct answer cannot be determined from the information given.

 

Ans:  A

Level of Difficulty:  Moderate

Section:  7.1.E

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

  1. In sickle-cell anemia, the negatively charged glutamic acid residue is replaced by the neutral amino acid ____________.
  2. A) tyrosine
  3. B) lysine
  4. C) valine
  5. D) adenosine
  6. E) glycine

 

Ans:  C

Level of Difficulty:  Moderate

Section:  7.1.E

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. Hemoglobin S, the variant responsible for the misshapen red blood cells characteristic of the disease sickle-cell anemia, is potentially advantageous to heterozygotes because it confers some level of resistance to the disease _________.
  2. A) rickets
  3. B) AIDS
  4. C) cyanosis
  5. D) polycythemia
  6. E) malaria

 

Ans:  E

Level of Difficulty:  Easy

Section:  7.1.E

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. ______of the world’s human population carries an inherited variant hemoglobin gene.
  2. A) 5%
  3. B) 25%
  4. C) 50%
  5. D) 75%
  6. E) 90%

 

Ans:  A

Level of Difficulty:  Easy

Section:  7.1.E

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin
44.  The repeating functional unit in a myofibril is called

  1. A) the A band.
  2. B) the I band.
  3. C) the sarcomere.
  4. D) the H zone.
  5. E) the M disk.

 

Ans:  C

Level of Difficulty:  Easy

Section:  7.2.A

Learning objective: Muscle Contraction

 

 

  1. Muscle contraction is directly caused by
  2. A) structural changes in actin.
  3. B) structural changes in myosin.
  4. C) structural changes in the A band.
  5. D) structural changes in the Z disk.
  6. E) None of the above is correct.

 

Ans:  E

Level of Difficulty:  Moderate

Section:  7.2.A

Learning objective: Muscle Contraction

 

 

  1. Muscle contraction is directly caused by
  2. A) structural changes in actin.
  3. B) structural changes in myosin.
  4. C) thick and thin filaments sliding past each other.
  5. D) structural changes in the Z disk.
  6. E) None of the above is correct.

 

Ans:  C

Level of Difficulty:  Easy

Section:  7.2.A

Learning objective: Muscle Contraction

  1. Which of the statements about muscle contraction is correct?
  2. A) During muscle contraction the sarcomere becomes shorter.
  3. B) During muscle contraction the I band becomes shorter.
  4. C) During muscle contraction the H zone becomes shorter.
  5. D) During muscle contraction the distance between the Z disk and the M disk becomes shorter.
  6. E) All of the answers above are correct.

 

Ans:  E

Level of Difficulty:  Moderate

Section:  7.2.A

Learning objective: Muscle Contraction

 

 

  1. Which of the statements about muscle contraction is not true?
  2. A) During muscle contraction the sarcomere becomes shorter.
  3. B) During muscle contraction the I band becomes shorter.
  4. C) During muscle contraction the H zone becomes shorter.
  5. D) During muscle contraction the A band becomes shorter
  6. E) During muscle contraction the distance between the Z disk and the M disk becomes shorter.

 

Ans:  D

Level of Difficulty:  Moderate

Section:  7.2.A

Learning objective: Muscle Contraction

 

 

  1. What are the main bonds or forces that stabilize the dimer formed by two myosin heavy chains?
  2. A) hydrophobic interactions
  3. B) hydrogen-bonds
  4. C) ionic interactions
  5. D) disulfide bonds
  6. E) isopeptide bonds

 

Ans:  A

Level of Difficulty:  Easy

Section:  7.2.A

Learning objective: Muscle Contraction

  1. During muscle contraction
  2. A) myosin pulls actin filaments toward the M disk.
  3. B) myosin pushes actin filaments toward the Z disk.
  4. C) actin pulls myosin toward the Z disk.
  5. D) actin pushes myosin toward the M disk.
  6. E) All of the answers above are correct.

 

Ans:  A

Level of Difficulty:  Easy

Section:  7.2.A

Learning objective: Muscle Contraction

 

 

  1. Which statement about myosin is not true?
  2. A) Myosin is a heterohexamer.
  3. B) Myosin contains two globular heads.
  4. C) Myosin contains six different polypeptides
  5. D) Myosin aggregates to form thick filaments
  6. E) All of the answers above are true of myosin.

 

Ans:  E

Level of Difficulty:  Easy

Section:  7.2.A

Learning objective: Muscle Contraction

 

 

  1. Which statement about actin is not true?
  2. There are two actin genes, one for F-actin and one for G-actin.
  3. Monomeric G-actin polymerizes to form F-actin.
  4. Actin filaments are polar (the ends can be distinguished).
  5. Actin can bind ATP.
  6. Actin is a common protein in nonmuscle cells.

 

Ans:  A

Level of Difficulty:  Moderate

Section:  7.2.A

Learning objective: Muscle Contraction

  1. The energy needed to drive muscle contraction comes from ATP hydrolysis that is carried out by
  2. A) G-actin.
  3. B) F-actin.
  4. C) myosin heads.
  5. D) myosin tails.
  6. E)

 

Ans:  C

Level of Difficulty:  Easy

Section:  7.2.B

Learning objective: Muscle Contraction

 

 

  1. During muscle contraction myosin heads
  2. A) walk along thick filaments toward the M disk.
  3. B) walk along thick filaments toward the Z disk.
  4. C) walk along thin filaments toward the M disk.
  5. D) walk along the thin filaments toward the H zone.
  6. E) walk along the thin filaments toward the Z disk.

 

Ans:  E

Level of Difficulty:  Moderate

Section:  7.2.B

Learning objective: Muscle Contraction

 

  1. Muscle contraction is triggered
  2. A) in response to an increase in the cytoplasmic Ca2+
  3. B) in response to a decrease in the cytoplasmic Ca2+
  4. C) in response to an increase in the cytoplasmic cAMP concentration.
  5. D) in response to a decrease in the cytoplasmic cAMP concentration.
  6. E) in response to an increase in the cytoplasmic titin concentration.

 

Ans:  A

Level of Difficulty:  Moderate

Section:  7.2.B

Learning objective: Muscle Contraction

  1. Which statement about actin is correct?
  2. A) Actin is expressed only in muscle.
  3. B) Actin is expressed at low levels in most cells.
  4. C) No known function has been described for actin in nonmuscle cells.
  5. D) Nonmuscle cells only contain G actin.
  6. E) Actin is the most abundant cytoplasmic protein in many cell types.

 

Ans:  E

Level of Difficulty:  Moderate

Section:  7.2.C

Learning objective: Muscle Contraction

 

  1. Which of the following statements about actin is not true?
  2. A) Actin is the most abundant cytoplasmic protein in many cell types.
  3. B) Actin forms microfilaments in many cell types.
  4. C) Actin plays an important role in endocytosis.
  5. D) Actin is present only as monomers in nonmuscle cells.
  6. E) Actin filaments are dynamic, they grow at one end and they lose subunits at the other end.

 

Ans:  D

Level of Difficulty:  Moderate

Section:  7.2.C

Learning objective: Muscle Contraction

 

  1. Treadmilling refers to
  2. A) myosin heads walking along actin microfilaments.
  3. B) actin and myosin filaments sliding along each other.
  4. C) actin monomers moving through a microfilament from the + end to the – end.
  5. D) synthesis and degradation of actin monomers.
  6. E) the interactions between actin and tropomyosin.

 

Ans:  C

Level of Difficulty:  Moderate

Section:  7.2.C

Learning objective: Muscle Contraction

  1. Humoral immunity refers to that part of the immune response that is mediated by
  2. A) T lymphocytes.
  3. B)
  4. C)
  5. D) the thymus.
  6. E) the skin.

 

Ans:  B

Level of Difficulty:  Easy

Section:  7.3.A

Learning objective: Antibodies

 

 

  1. Humoral immunity is mediated by soluble molecules. Which cell type produces the soluble molecules that carry out the humoral immunity?
  2. A) T cells
  3. B) B cells
  4. C) macrophages
  5. D) neutrophils
  6. E) monocytes

 

Ans:  B

Level of Difficulty:  Easy

Section:  7.3.A

Learning objective: Antibodies

 

 

  1. How many different classes of antibodies are produced by the human immune system?
  2. A) 1
  3. B) 2
  4. C) 3
  5. D) 4
  6. E) 5

 

Ans:  E

Level of Difficulty:  Easy

Section:  7.3.A

Learning objective: Antibodies

  1. IgG is the most common immunoglobulin in the circulatory system and in the extravascular fluid. It is composed of two light chains and two heavy chains.  What is the approximate molecular mass of an IgG molecule?
  2. A) 23 kDa
  3. B) 75 kDa
  4. C) 150 kDa
  5. D) 360 kDa
  6. E) 950 kDa

 

Ans:  C

Level of Difficulty:  Moderate

Section:  7.3.A

Learning objective: Antibodies

 

  1. IgG is one of five classes of antibodies that can be produced by our immune system. IgGs have a molecular mass of approximately 150 kDa, what is their subunit composition?
  2. A) 2 light chains and 2 heavy chains
  3. B) 2 light chains, 2 heavy chains, and a J chain
  4. C) 4 light chains, 4 heavy chains, and a J chain
  5. D) 6 light chains, 6 heavy chains, and a J chain
  6. E) 10 light chains, 10 heavy chains , and a J chain.

 

Ans:  A

Level of Difficulty:  Easy

Section:  7.3.A

Learning objective: Antibodies

 

 

  1. Which class of antibodies has been implicated in allergic reactions?

 

  1. A) IgA
  2. B) IgD
  3. C) IgE
  4. D) IgG
  5. E) IgM

 

Ans:  C

Level of Difficulty:  Moderate

Section:  7.3.A

Learning objective: Antibodies

  1. How many antigen-binding sites are present on an IgG molecule?
  2. A) 1
  3. B) 2
  4. C) 3
  5. D) 4
  6. E) 5

 

Ans:  B

Level of Difficulty:  Easy

Section:  7.3.A

Learning objective: Antibodies

 

 

  1. How many antigen-binding sites are present on an IgM molecule?
  2. A) 2
  3. B) 4
  4. C) 10
  5. D) 16
  6. E) 25

 

Ans:  C

Level of Difficulty:  Moderate

Section:  7.3.A

Learning objective: Antibodies

 

 

  1. Fab fragments can be generated by
  2. A) reduction of IgG molecules.
  3. B) oxidation of IgG molecules.
  4. C) limited digestion of IgG molecules with papain.
  5. D) combining two light chains.
  6. E) combining two heavy chains.

 

Ans:  C

Level of Difficulty:  Moderate

Section:  7.3.A

Learning objective: Antibodies

  1. Which statement about antigen-binding sites in antibodies is false?
  2. A) An antigen-binding site on an IgG is formed by the amino-terminal ~110 amino acids of a light chain and the amino terminal ~110 amino acids of a heavy chain.
  3. B) An antigen-binding site on an IgG is formed by the variable region of a light chain and the variable region of a heavy chain.
  4. C) The antigen-binding site is composed of two Ig folds.
  5. D) Antigen-binding specificity is determined by the sequences of the hypervariable sequences in both the light chain and the heavy chain.
  6. E) Antigen binding specificity is determined exclusively by the sequences in the carboxy-terminal ~110 amino acids in the light chain and the heavy chain.

 

Ans:  E

Level of Difficulty:  Moderate

Section:  7.3.B

Learning objective: Antibodies

 

 

  1. The Ig fold can be described as a
  2. A) globular fold composed of a
  3. B) a globular fold composed of a four helix bundle.
  4. C) a globular fold composed of a b
  5. D) a globular fold composed of b
  6. E) a coiled-coil.

 

Ans:  C

Level of Difficulty:  Moderate

Section:  7.3.B

Learning objective: Antibodies

SHORT ANSWER

 

 

  1. Myoglobin is an oxygen binding protein in muscle. Describe in one sentence the overall structure of myoglobin.

 

Ans:  Myoglobin is a globular protein composed of 8 a helices that forms a hydrophobic pocket that contains the heme group.

Level of Difficulty:  Moderate

Section:  7.1.A

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. What is the primary physiological function of myoglobin in most mammals?

 

Ans:  The primary physiological function of myoglobin in most mammals is to increase the solubility for O2 in muscle tissue and thereby increasing the diffusion rate.

Level of Difficulty:  Moderate

Section:  7.1.A

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. It appears that the heme group in myoglobin binds the O2. What is the function of the polypeptide?

 

Ans:  The polypeptide performs various functions:  1.  The polypeptide provides solubility for the heme group, which is very non-polar.  2. The polypeptide prevents permanent oxidation of the Fe(II).  3.  The polypeptide helps coordinate the Fe(II) (His F8)  4.  The polypeptide forms a H-bond with the O2 (His E7).

Level of Difficulty:  Difficult

Section:  7.1.A

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

 

 

  1. Mammals and other animals have a circulatory system because diffusion is to slow to supply the tissues with oxygen in animals that are larger than 2 millimeter. Explain in one sentence why these circulatory systems contain hemoglobin or other oxygen binding proteins?

 

Ans:  Oxygen-binding proteins increase the solubility of oxygen in the fluid of the circulatory system.  This is important because oxygen is not very soluble in aqueous solutions.

Level of Difficulty:  Difficult

Section:  7.1.B

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

  1. The graph below shows the O2-binding curves for myoglobin (Mb) and hemoglobin (Hb).
  2. Label the two curves (indicate which one represents Mb and which one represents Hb).

 

 

  1. Use the graph to determine the Kd of myoglobin for O2 (show your approach).
  2. What is the difference between myoglobin and hemoglobin that cause the O2-binding curves to so be different?
  3. Why is it important that hemoglobin has these particular O2-binding characteristics?

 

Ans:  a.  See graph.

  1. Kd equals 3-4 torr (see graph).
  2. Mb has one subunit, Hb has 4 subunits. The sigmoid binding curve is a consequence of positive cooperativity between the 4 O2-binding sites in Hb.  The hyperbolic binding curve for myoglobin is the result of oxygen binding reaction being noncooperative.
  3. As a consequence of positive cooperation Hb has a high affinity for O2 when the O2 concentration is high (in the lungs) and low affinity for O2 when the O2 concentration is low (in the tissues). As a consequence Hb binds large amount of O2 in the lungs and releases large amounts of O2 in the tissues, resulting in efficient transport of O2.

Level of Difficulty:  Difficult

Section:  7.1.B

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin

  1. You have been studying O2 binding to a hemerythrin-like protein isolated from an exotic marine worm. Your O2-binding data are shown in the table below.
  2. Use the data to generate an O2-binding curve (do not forget to mark the axes).
  3. Use the curve to estimate the Kd for the interaction.
  4. Is there any evidence from your data that this hemoglobin-like protein binds O2 in a cooperative manner (briefly explain your answer)?

 

 

[Ligand] in µM Y
21 0.11
42 0.28
79 0.37
118 0.42
257 0.58
362 0.66
535 0.78
745 0.86
900 0.89
1052 0.92

 

 

 

 

 

Ans:  a.  see curve

  1. see curve, Kd equals 180 µM
  2. there is no evidence for cooperative binding of O2 to this protein, because the binding curve is hyperbolic and not sigmoid.

Level of Difficulty:  Difficult

Section:  7.1.B

Learning objective: Oxygen Binding to Myoglobin and Hemoglobin