In considering protein secondary structure which of the following is INCORRECT?
- A) An α helix repeats after 18 residues and has 3.6 residues per turn.
- B) A network of main-chain hydrogen bonds connect β strands in a β sheet.
- C) The most common structures are the α helix and the β sheet.
- D) The 310helix is right-handed and often contains proline residues.
- E) The β strands can be in either parallel or antiparallel configuration.
Answer: D
Objective: 6.1
Global LO: G2
2) The amino acid side chain residues in an α helix point outwards away from the center of the helix.
Answer: TRUE
Objective: 6.1
Global LO: G2
3) ________ between amide protons and carbonyl oxygens is necessary to stabilize a regular folding of protein secondary structure.
Answer: Hydrogen bonding
Objective: 6.1
Global LO: G7
4) A ________ plot describes which structures in a polypeptide are sterically possible and which are not based on the angles of rotation about the backbone Namide —Cα and Cα-Ccarbonyl bonds.
Answer: Ramachandran
Objective: 6.3
Global LO: G9
5) Which of the following statements about α-keratins is FALSE?
- A) They include a major class of protein that comprises hair, fingernails and animal skin.
- B) Individual molecules are α-helical.
- C) There is a strip of contiguous hydrophobic surface making a shallow spiral around the helix.
- D) They include a small globular regions covalently linked to the surface.
- E) Pairs of α-helices twist about each other in a coiled-coil structure held together entirely by hydrophobic interactions.
Answer: E
Objective: 6.4
Global LO: G7
6) The protein that makes up about a third of the total protein mass in animals is:
- A) β-keratin.
- B) collagen.
- C) hemoglobin.
- D) myoglobin.
- E) α-keratin.
Answer: B
Objective: 6.4
Global LO: G7
7) Fibroin is a β-sheet protein, with a high proportion of glycine.
Answer: TRUE
Objective: 6.4
Global LO: G7
8) Tropocollagen is a double helix of two left-handed polypeptide chains.
Answer: FALSE
Objective: 6.4
Global LO: G7
9) Scurvy results in weakness in collagen fibres because the enzymes that catalyze ________ of proline and lysine residues in collagen require Vitamin C.
Answer: hydroxylation
Objective: 6.4
Global LO: G7
10) Which of the following is CORRECT when considering the tertiary structure of globular proteins?
- A) β sheets are usually twisted or wrapped into barrel structures.
- B) Hydrophobic residues are normally on the inside and hydrophilic residues are on the outside.
- C) The amino acid proline never occurs in a region where the polypeptide chain bends or turns.
- D) All parts of the proteins can be classified as helix, β sheet or turns.
- E) None of the above.
Answer: B
Objective: 6.6
Global LO: G7
11) Proteins cannot self-assemble into a functional conformation after they have been denatured.
Answer: FALSE
Objective: 6.6
Global LO: G2
12) Protein folding is a random process, whereby a vast number of possible conformations are tested to find the desired most stable state.
Answer: FALSE
Objective: 6.7
Global LO: G2
13) The folded conformation of proteins can be stabilized by the binding of a metal ion or cofactor.
Answer: TRUE
Objective: 6.9
Global LO: G7
14) The interactions that stabilize multisubunit complexes are different to those that stabilize tertiary structure.
Answer: FALSE
Objective: 6.9
Global LO: G7
15) Protein folding is a thermodynamically favorable process under physiological conditions because:
- A) there is an increase in entropy associated with protein folding.
- B) there is a decrease in entropy of the solvent by burying hydrophobic groups within the molecule.
- C) of the large negative enthalpy change associated with many noncovalent interactions.
- D) no intermediate stage disulphide bonds form during the folding process.
- E) all of the above.
Answer: C
Objective: 6.10
Global LO: G7
16) The cavity in the GroEL-GroES complex from E. coli provides a favorable environment that prevents ________ and mis-folding.
Answer: aggregation
Objective: 6.11
Global LO: G7
17) Bovine spongiform encephalopathy is an infectious disease caused by a prion protein, which undergoes a ________ change to become pathogenic.
Answer: conformational
Objective: 6.12
Global LO: G7
18) Proteins have an asymmetrical tertiary structure, while multisubunit proteins can exhibit several types of symmetry.
Answer: TRUE
Objective: 6.14
Global LO: G7
19) The functional organization of proteins where specific complexes of two or more polypeptides are formed is called ________ structure.
Answer: quaternary
Objective: 6.14
Global LO: G7
20) Which technique is able to investigate secondary structural features of proteins?
- A) Infrared spectroscopy
- B) Ultraviolet spectroscopy
- C) Fluorescence spectroscopy
- D) Circular dichroism
- E) All of the above
Answer: E
Objective: 6.15
Global LO: G9
21) ________ spectroscopy can be used to study dynamic processes in solution.
Answer: Nuclear magnetic resonance
Objective: 6.15
Global LO: G9
22) SDS gel electrophoresis can be used to determine:
- A) whether subunits in a protein complex are identical or not.
- B) the molecular mass of a native protein complex.
- C) the overall charge on a polypeptide.
- D) the molecular mass of denatured protein subunits.
- E) none of the above.
Answer: D
Objective: 6.18
Global LO: G9
Biochemistry: Concepts and Connections (Appling et al.)
Chapter 7 Protein Function and Evolution
1) Which of the following is NOT true of immunoglobulin molecules?
- A) They consist of four polypeptide chains held together by disulphide bridges.
- B) They have two identical heavy chains and two identical light chains.
- C) Antigenic determinants reside only in the variable region of the light chains.
- D) Proteolytic cleavage can generate fragments containing the antigen-binding site.
- E) Some are membrane bound.
Answer: C
Objective: 7.3
Global LO: G2
2) The immunoglobulin domain is a stable scaffold containing two antiparallel β- sheets upon which to display hypervariable loops.
Answer: TRUE
Objective: 7.3
Global LO: G7
3) The specific interaction between an antibody and antigen occurs by virtue of both shape and ________ complementarity.
Answer: charge
Objective: 7.4
Global LO: G7
4) Which of the following statements is FALSE?
- A) Myoglobin is a single polypeptide chain folded about a heme prosthetic group.
- B) Hemoglobin is a tetramer, each of which binds a heme group.
- C) In both hemoglobin and myoglobin, iron is chelated by a tetrapyrole ring system.
- D) The iron in both hemoglobin and myoglobin has two coordination sites that bind to oxygen.
- E) Hydrogen bonding to a histidine residue assists stabilization of the Fe2+-O2complex in both hemoglobin and myoglobin.
Answer: D
Objective: 7.9
Global LO: G2
5) Both myoglobin and hemoglobin exhibit cooperative binding to oxygen.
Answer: FALSE
Objective: 7.9
Global LO: G2
6) The conserved residues in the hemoglobins and myoglobins include the ________ proximal and distal to the heme iron.
Answer: histidines
Objective: 7.9
Global LO: G7
7) The ________ binding of oxygen to hemoglobin is facilitated by changes in protein conformation upon oxygen binding to one subunit that affect the binding of oxygen to another subunit.
Answer: cooperative
Objective: 7.12
Global LO: G2
8) Which of the following observations helps to explain the conformational changes that occur in hemoglobin upon binding to oxygen?
- A) The four heme groups are positioned close to the surface of the molecule.
- B) An αβ dimer rotates and slides with respect to the other dimer upon binding oxygen.
- C) Neither the heme nor the iron ion in the deoxy conformation is in a planar conformation.
- D) All of the above
- E) B and C
Answer: E
Objective: 7.14
Global LO: G2
9) Fetal hemoglobin has a higher affinity for oxygen than does maternal hemoglobin because it has a higher affinity for the allosteric regulator 2,3-bisphosphoglycerate.
Answer: FALSE
Objective: 7.16
Global LO: G7
10) The production of carbon dioxide during respiration in aerobic tissues lowers the pH in erythrocytes, which in turn ________ the affinity of oxygen binding to hemoglobin.
Answer: decreases
Objective: 7.18
Global LO: G2
11) Comparison of globin sequences from many different species suggests that myoglobin and hemoglobin have evolved from a single myoglobin-like protein.
Answer: TRUE
Objective: 7.21
Global LO: G7
12) The sickle cell mutation causes oxyhemoglobin molecules to ________ due to hydrophobic interactions because a glutamate residue is replaced with a valine.
Answer: aggregate
Objective: 7.22
Global LO: G7
13) Which of the following statements about muscle contraction is TRUE?
- A) ATP hydrolysis releases myosin from actin.
- B) ATP hydrolysis results in strong binding of myosin to actin.
- C) ATP hydrolysis causes a conformational change in the myosin head.
- D) Muscle contraction occurs as ATP is hydrolyzed.
- E) ATP hydrolysis must occur before the actin-binding site closes.
Answer: C
Objective: 7.23
Global LO: G7
14) The heavy chain of the muscle form of myosin:
- A) forms a coiled-coil structure with a globular head domain.
- B) contains the motor domain within the C-terminal region.
- C) is a complex of 540 kDa.
- D) binds ATP near the C-termini.
- E) has two covalently bound light chains.
Answer: A
Objective: 7.24
Global LO: G7
15) F-actin is a polymer of G-actin monomers and exhibits symmetry.
Answer: FALSE
Objective: 7.24
Global LO: G7
16) The A band of skeletal muscle is formed by noncovalent cross-bridges between the thin filaments that are mainly ________ and the thick filaments that are mainly ________.
Answer: actin, myosin
Objective: 7.25
Global LO: G7
17) The most critical substance in stimulating muscle contraction is:
- A) ATP.
- B) Ca2+.
- C) tropomyosin.
- D) troponin C.
- E) troponin T.
Answer: B
Objective: 7.27
Global LO: G7
18) Calcium regulates muscle contraction by binding to:
- A) actin.
- B) myosin.
- C) tropomyosin.
- D) troponin C.
- E) troponin T.
Answer: D
Objective: 7.27
Global LO: G7
19) The greatest conformational change in the neck piece of myosin occurs during ATP hydrolysis.
Answer: FALSE
Objective: 7.27
Global LO: G7
20) The concentration of Ca2+ in the myoplasm can increase as much as 10,000 fold in response to a motor nerve impulse.
Answer: TRUE
Objective: 7.27
Global LO: G7
21) Antibodies cannot be used to purify proteins because the antibody-antigen interaction is too strong.
Answer: FALSE
Objective: 7.28
Global LO: G9
22) Enzyme-linked immunosorbent assay, western blotting and immunofluorescent light microscopy all make use of the specific interaction between an antigen and an ________.
Answer: antibody
Objective: 7.28
Global LO: G9
