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Questions in this quiz (50)
1In a protein, the most conformationally restricted amino acid is ______; the least conformationally restricted is
- ATrp, Gly
- BMet, Cys
- CPro, Gly
- DIle, Ala
- EAla, Pro
2Which one of these characteristics is not true for the helix?
- AThere are 3.6 amino acids per turn.
- BThere is a requirement for glycine every third amino acid residue.
- CA 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.
- DProline is typically not found in the helix.
- EIt is right-handed.
3Which of these characteristics does not describe the sheet?
- AAmino acid side chains are located both above and below the sheet.
- BB-sheets have a pleated edge-on appearance.
- CThey can exist in either parallel or antiparallel configurations.
- DThe sheets contain as few as two and as many as 22 polypeptide chains.
- EParallel B-sheets containing fewer than five chains are the most common
4Which statement below does not describe fibrous proteins?
- ADomains have a globular fold
- BThese proteins usually contain only one type of secondary structure.
- CThese proteins usually exhibit structural or protective characteristics.
- DThese proteins have usually elongated hydrophilic surfaces.
- EThese proteins are usually insoluble in water.
5Which of the following changes would not alter the functional characteristics of α keratin?
- AIncreasing the number of residues per turn to 4.1 while maintaining the same amino acid sequence.
- BSubstitution of a hydrophilic amino acid for a hydrophobic amino acid at position a and d of the 7-residue pseudorepeat.
- CDecreasing the number of cysteine amino acids within each protofilament
- DChanging the environment surrounding the protein to one that is more reductive
- EAll of the above would alter the functional characteristics of keratin
6Which of the following statements is true regarding collagen?
- AThe inability to hydroxylate proline results in the inability to synthesize collagen.
- BThe α helical structure is ideal for intertwining 3 filaments.
- CHydrogen bonds between the ─OH groups of Hyp residues stabilize the helix.
- DThe requirement for glycine every 3rd amino acid is essential for the triplet helix formation.
- EOn average, there is one proline for every hydroxyproline.
7Which of the following gives the best example of a nonrepetitive structure in a protein?
- Aa random sequence of 12 amino acids with high Pα values forming an α helix
- Ban amino acid sequence with the following pattern "…a-b-c-d-e-a-b-c-d-a-b-c-d…"
- Ca 13 residue α helix with a Gln at position n+12 which hydrogen bonds to a residue at position n+10
- DAll of the above statements describe nonrepetitive protein structures.
- ENone of the above describe nonrepetitive protein structures.
8In the absence of ascorbic acid, prolyl oxidase is unable to oxidize proline residues in collagen to hydroxyproline, resulting in:
- Alathyrism
- Bprion diseases
- Camyloid formation
- Dscurvy
- Eallysine
9Of the following, which amino acid is most likely to be found in position 1 or 4 on α keratin?
- Aphe
- Bala
- Clys
- Dtrp
- Epro
10Which of the following amino acids combinations have side chains with groups that have the greatest ability to stabilize the tertiary structure of a protein?
- ALys and Arg
- BCys and Glu
- CGlu and Lys
- DGln and Glu
- EPro and Asp
11The low pH found in the gut can enhance the digestibility of dietary protein by causing
- Aamide hydrolysis
- Bprotein denaturation
- Cdisulfide reduction
- Dprion formation
- Ecysteine oxidation
12Which of the following occurs first when folding a disordered polypeptide chain into a stable protein formation?
- Aformation of a low energy state
- Bassociation of ordered subunits
- Caggregation of hydrophobic regions in the protein
- Dtertiary structure refinement
- Eformation of a low entropy state
13Imagine 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?
I. Nonpolar portions of the protein become more soluble.
II. The protein begins to denature ,
III. The protein stability increases due to hydrophobic collapse- AI,II,III
- BI, II
- CII, III
- DI, III
- EII
14For B-sheets, the terms ‘parallel’ and ‘antiparalllel’ refer to ___________.
- Athe ‘direction’ of the associated peptide strands
- Bthe orientation of the amide cross-links
- Cthe quaternary structure of the protein
- Dthe orientation of the hydrogen bonding
- Ethe topology of the reverse turns
15In general molecular chaperone proteins function by
- Amediating disulfide bond formation
- Bsynthesizing new proteins when one is misfolded.
- Cpreventing premature folding by binding hydrophobic regions of the protein.
- Denhancing salt bridge formation.
- Enone of the above
16When comparing similarities among multiple protein structures, which of the following is false?
- AProteins with the same function from a different species are likely to have similar motifs.
- BProteins with the same function from different species are likely to be more similar in sequence than in structure.
- CAn effective protein motif isl likely be observed in multiple proteins.
- DProteins with the same motifs are likely to perform similar functions.
- ENone of the above statements are false
17The structure and sequence of a protein of unknown function was examined. Which of the following provides the best prediction of the protein's function?
- Athe observation of several disordered α helical domains.
- Bthe observation of multiple protein subunits.
- Cthe observation of motif known as the Rossmann fold.
- Dthe observation of a large number of random coil regions.
- EAll of the above offer excellent prediction of the protein's function
18Noncovalent forces that stabilize protein structure include all of the following except
- Athe hydrophobic effect
- Bsalt bridges
- Celectrostatic interactions with metal ions
- Dhydrogen bonding
- Edisulfide bridges
19The classic experiment demonstrating that reduced and denatured RNase A could refold into the native form demonstrates that:
- A1° structure can determine 3° structure
- Bdenaturation does not disrupt protein 2° structure
- Cdisulfide bonds do not stabilize folded proteins
- DAll of the above.
- ENone of the above
20The first step in the folding of disordered polypeptides into ordered functional protein is the formation of ______.
- A1 structure
- B2 structure
- C3 structure
- D4 structure
- Ehydrogen bonds
21Evolutionary processes have
- Aincreased the stability of 4° structures.
- Bdecreased the number of subunits.
- Cincreased similarity amount 1° structures.
- Denhanced efficient folding pathways.
- Eall of the above
22Chaperonins such as the GroEL/ES system
- Afunction with thermophilic proteins only.
- Bare required at low pH
- Crequire ATP hydrolysis
- Din vitro only.
- Efunction in a nonaqueous environment.
23Protein diseases can be caused by which of the following
- Amutations affecting the 1° structure.
- Bmutations affecting the 3° structure.
- Cchanges in the post-synthetic processing of proteins.
- DAll of the above are potential causes.
- ENone of the above are potential causes
24Which of the following would be most stable based on the information you have learned about protein structure?
- Aa loop region with 8 amino acids
- Ba β sheet region made up of amino acids Val, Ile, Phe
- Can α helix made up of Cys, Pro, and Phe
- Da β hairpin with 12 amino acids
- EAll have equal stability.
25Hydrogen bonds and maximum separation of amino acid side chains make the _____very stable and energetically ______________.
- Aα helix and β sheet, favorable
- Bα helix, unfavorable
- Cβ sheet, unfavorable
- Dα helix, favorable
- Eβ sheet, favorable
26A chaperonin
- Ahelps fold some proteins in their lowest energy state.
- Bis required for all proteins to fold properly.
- Cmediates the unfolding of proteins.
- Dis required for protein denaturation
- Ecounteracts the laws of thermodynamics.
27A 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?
- AIt has 3.6 residues per turn.
- BIt is a random coil, not a helix.
- CIt is an α helix.
- DIt has more residues per turn than an α helix.
- EIt has fewer residues per turn than an α helix.
28Which of the following contribute to the minimization of energy that occurs with protein folding?
- Aorientating amino acid groups to maximize hydrogen bonding
- Bfolding hydrophobic groups towards the exterior of the protein
- Cburying polar groups towards the interior of the protein
- Dextensive cavity formation
- Eall of the above
29Which 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)?
- Aaggregation of a misfolded protein
- Baggregation of random coil regions on a protein
- Cingestion of ammonium salts
- Dthe serious side effects of experimental treatment with Quinacrine
- EAll are potential causes Creutzfeld-Jakob disease.
30Proteins can denature due to a change in
- ApH
- Btemperature
- Cionic strength
- Dall of the above
- Enone of the above
3148. 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)
I. Pro-Hyp-Gly-Pro-Hyp-Gly-Pro-Hyp-Gly
II. Pro-Flp-Gly-Pro-Flp-Gly-Pro-Flp-Gly
III. Gly-Pro-Thr-Gly-Pro-Thr-Gly-Pro-Thr- A“1” because Hyp has OH groups
- B“1” because the electronegativity of oxygen is greater
- C“2” because the electronegativity of proline is greater
- D“3” because Thr is a small amino acid which allows close packing
32Based 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- Aalpha-keratin
- Bbeta-keratin
- Ccollagen
- Dpleated collagen
33Which of the following structural proteins has the greatest elasticity?
- Aalpha-keratin
- Bbeta-keratin
- Ccollagen
- Dpleated collagen
34Noncovalent interactions account for the strength of which of the following structural proteins?
- Aalpha-keratin
- Bcollagen
- Cpleated collagen
- DA and B
- EB and C
35When considering fibrous proteins, which of the following statements is TRUE?
- Anoncovalent interactions contribute to the strength of all these proteins
- Ball of them consist of alpha-helix structure
- Call of them require vit C
- Ddecrease in amounts of any of them cause scurvy
- Eall of these are true of fibrous proteins
36Which of the characteristics of collagen structure listed below contrubute to the tensi
le strength of collagen?
I. Collagen is made up of a triplet helix where 3 left-handed helices twist together in a right handed sense.
II. 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.- AI
- BI, II
- CI, II, III
- DII, III
- EI, III
37Molecular chaperones bind to unfolded or partially folded polypeptide chains in order to accomplish which of the following?
- Aensure that improper aggregation of hydrophobic segments does not occur
- Bengulf the protein in order to ensure that the protein is not damaged by heat denaturation
- Cfacilitate native folding by exposing hydrophobic segments of the protein as it is synthesized
- Dfacilitate aggregation of multiple subunits of a protein during synthesis
- EAll of the above are accomplished by molecular chaperones.
38What observation about protein refolding or renaturation helped to solidify the connection between primary amino acid sequence and 3-D structure?
- ASpontaneous refolding of proteins into their native state under physiologic conditions.
- BAssisted refolding of proteins into their native state under laboratory conditions.
- CIdentification of thermostable proteins than maintain their native state in adverse temperatures.
- DA and B
- EB and C
39Native 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?
- AProteins with hydrophobic groups on the interior would maintain their native state.
- BProteins with hydrophilic groups on the exterior would denature and likely precipitate
- CProteins with exposed hydrophobic groups would maintain their structure and remain in solution
- DBoth A and B would occur.
- EBoth B and C would occur.
40When 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?
I. Leucine vs. Isoleucine
II. Phenylalanine vs. Alanine
III. Glutamate vs. Glutamic acid- AThose in both groups I and II could be differentiated
- BThose in both groups I and III could be differentiated
- COnly those in group II could be differentiated
- DOnly those in group III could be differentiated
- EOnly those in groupI could be differentiated
41The most important contribution to the stability of a protein’s conformation appears to be the:
- Aentropy increase from the decrease in ordered water molecules forming a solvent shell around it.
- Bmaximum entropy increase from ionic interactions between the ionized amino acids in a protein.
- Csum of free energies of formation of many weak interactions among the hundreds of amino acids in a protein
- Dsum of free energies of formation of many weak interactions between its polar amino acids and surrounding water
- Estabilizing effect of hydrogen bonding between the carbonyl group of one peptide bond and the amino group of another.
42In an aqueous solution, protein conformation is determined by two major factors. One is the formation of the maximum number of hydrogen bonds. The other is the:
- Aformation of the maximum number of hydrophilic interactions.
- Bmaximization of ionic interactions.
- Cminimization of entropy by the formation of a water solvent shell around the protein.
- Dplacement of hydrophobic amino acid residues within the interior of the protein.
- Eplacement of polar amino acid residues around the exterior of the protein.
43In an alpha-helix, the R groups on the amino acid residues:
- Aalternate between the outside and the inside of the helix.
- Bare found on the outside of the helix spiral.
- Ccause only right-handed helices to form.
- Dgenerate the hydrogen bonds that form the helix.
- Estack within the interior of the helix.
44The major reason that antiparallel beta-stranded protein structures are more stable than parallel beta-stranded structures is that the latter:
- Aare in a slightly less extended configuration than antiparallel strands.
- Bdo not have as many disulfide crosslinks between adjacent strands.
- Cdo not stack in sheets as well as antiparallel strands.
- Dhave fewer lateral hydrogen bonds than antiparallel strands.
- Ehave weaker hydrogen bonds laterally between adjacent strands.
45The three-dimensional conformation of a protein may be strongly influenced by amino acid residues that are very far apart in sequence. This relationship is in contrast to secondary structure, where the amino acid residues are:
- Aalways side by side
- Bgenerally near each other in sequence
- Cinvariably restricted to about 7 of the 20 standard amino acids
- Doften on different polypeptide strands
- Eusually near the polypeptide chain’s amino terminus or carboxyl terminus
46Proteins often have regions that show specific, coherent patterns of folding or function. These regions are called:
- Adomains
- Boligomers
- Cpeptides
- Dsites
- Esubunits
47An average protein will not be denatured by
- Aa detergent such as sodium dodecyl sulfate.
- Bheating to 90°C
- Ciodoacetic acid
- DpH 10.
- Eurea.
48Which of the following is least likely to result in protein denaturation?
- Aaltering net charge by changing pH
- Bchanging the salt concentration
- Cdisruption of weak interactions by boiling
- Dexposure to detergents
- Emixing with organic solvents such as acetone
49Protein S will fold into its native conformation only when protein Q is also present in the solution. However, protein Q can fold into its native conformation without protein S. Protein Q, therefore, may function as a ____________ for protein S.
- Aligand
- Bmolecular chaperone
- Cprotein precursor
- Dstructural motif
- Esupersecondary structural unit
50Which of the following is not known to be involved in the process of assisted folding of proteins?
- Achaperonins
- Bdisulfide interchange
- Cheat shock proteins
- Dpeptide bond hydrolysis
- Epeptide bond isomerization
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- prot 3d
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- Aly Lzo
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