Aly Lzo
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Aly Lzo
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Question 1 of 50

1

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

Select one of the following:

  • Trp, Gly

  • Met, Cys

  • Pro, Gly

  • Ile, Ala

  • Ala, Pro

Explanation

Question 2 of 50

1

Which one of these characteristics is not true for the  helix?

Select one of the following:

  • There are 3.6 amino acids per turn.

  • There is a requirement for glycine every third amino acid residue.

  • 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.

  • Proline is typically not found in the  helix.

  • It is right-handed.

Explanation

Question 3 of 50

1

Which of these characteristics does not describe the  sheet?

Select one of the following:

  • Amino acid side chains are located both above and below the sheet.

  • B-sheets have a pleated edge-on appearance.

  • They can exist in either parallel or antiparallel configurations.

  • The sheets contain as few as two and as many as 22 polypeptide chains.

  • Parallel B-sheets containing fewer than five chains are the most common

Explanation

Question 4 of 50

1

Which statement below does not describe fibrous proteins?

Select one of the following:

  • Domains have a globular fold

  • These proteins usually contain only one type of secondary structure.

  • These proteins usually exhibit structural or protective characteristics.

  • These proteins have usually elongated hydrophilic surfaces.

  • These proteins are usually insoluble in water.

Explanation

Question 5 of 50

1

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

Select one of the following:

  • Increasing the number of residues per turn to 4.1 while maintaining the same amino acid sequence.

  • Substitution of a hydrophilic amino acid for a hydrophobic amino acid at position a and d of the 7-residue pseudorepeat.

  • Decreasing the number of cysteine amino acids within each protofilament

  • Changing the environment surrounding the protein to one that is more reductive

  • All of the above would alter the functional characteristics of keratin

Explanation

Question 6 of 50

1

Which of the following statements is true regarding collagen?

Select one of the following:

  • The inability to hydroxylate proline results in the inability to synthesize collagen.

  • The α helical structure is ideal for intertwining 3 filaments.

  • Hydrogen bonds between the ─OH groups of Hyp residues stabilize the helix.

  • The requirement for glycine every 3rd amino acid is essential for the triplet helix formation.

  • On average, there is one proline for every hydroxyproline.

Explanation

Question 7 of 50

1

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

Select one of the following:

  • a random sequence of 12 amino acids with high Pα values forming an α helix

  • an amino acid sequence with the following pattern "…a-b-c-d-e-a-b-c-d-a-b-c-d…"

  • a 13 residue α helix with a Gln at position n+12 which hydrogen bonds to a residue at position n+10

  • All of the above statements describe nonrepetitive protein structures.

  • None of the above describe nonrepetitive protein structures.

Explanation

Question 8 of 50

1

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

Select one of the following:

  • lathyrism

  • prion diseases

  • amyloid formation

  • scurvy

  • allysine

Explanation

Question 9 of 50

1

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

Select one of the following:

  • phe

  • ala

  • lys

  • trp

  • pro

Explanation

Question 10 of 50

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?

Select one of the following:

  • Lys and Arg

  • Cys and Glu

  • Glu and Lys

  • Gln and Glu

  • Pro and Asp

Explanation

Question 11 of 50

1

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

Select one of the following:

  • amide hydrolysis

  • protein denaturation

  • disulfide reduction

  • prion formation

  • cysteine oxidation

Explanation

Question 12 of 50

1

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

Select one of the following:

  • formation of a low energy state

  • association of ordered subunits

  • aggregation of hydrophobic regions in the protein

  • tertiary structure refinement

  • formation of a low entropy state

Explanation

Question 13 of 50

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?
I. Nonpolar portions of the protein become more soluble.
II. The protein begins to denature ,
III. The protein stability increases due to hydrophobic collapse

Select one of the following:

  • I,II,III

  • I, II

  • II, III

  • I, III

  • II

Explanation

Question 14 of 50

1

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

Select one of the following:

  • the ‘direction’ of the associated peptide strands

  • the orientation of the amide cross-links

  • the quaternary structure of the protein

  • the orientation of the hydrogen bonding

  • the topology of the reverse turns

Explanation

Question 15 of 50

1

In general molecular chaperone proteins function by

Select one of the following:

  • mediating disulfide bond formation

  • synthesizing new proteins when one is misfolded.

  • preventing premature folding by binding hydrophobic regions of the protein.

  • enhancing salt bridge formation.

  • none of the above

Explanation

Question 16 of 50

1

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

Select one of the following:

  • Proteins with the same function from a different species are likely to have similar motifs.

  • Proteins with the same function from different species are likely to be more similar in sequence than in structure.

  • An effective protein motif isl likely be observed in multiple proteins.

  • Proteins with the same motifs are likely to perform similar functions.

  • None of the above statements are false

Explanation

Question 17 of 50

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?

Select one of the following:

  • the observation of several disordered α helical domains.

  • the observation of multiple protein subunits.

  • the observation of motif known as the Rossmann fold.

  • the observation of a large number of random coil regions.

  • All of the above offer excellent prediction of the protein's function

Explanation

Question 18 of 50

1

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

Select one of the following:

  • the hydrophobic effect

  • salt bridges

  • electrostatic interactions with metal ions

  • hydrogen bonding

  • disulfide bridges

Explanation

Question 19 of 50

1

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

Select one of the following:

  • 1° structure can determine 3° structure

  • denaturation does not disrupt protein 2° structure

  • disulfide bonds do not stabilize folded proteins

  • All of the above.

  • None of the above

Explanation

Question 20 of 50

1

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

Select one of the following:

  • 1 structure

  • 2 structure

  • 3 structure

  • 4 structure

  • hydrogen bonds

Explanation

Question 21 of 50

1

Evolutionary processes have

Select one of the following:

  • increased the stability of 4° structures.

  • decreased the number of subunits.

  • increased similarity amount 1° structures.

  • enhanced efficient folding pathways.

  • all of the above

Explanation

Question 22 of 50

1

Chaperonins such as the GroEL/ES system

Select one of the following:

  • function with thermophilic proteins only.

  • are required at low pH

  • require ATP hydrolysis

  • in vitro only.

  • function in a nonaqueous environment.

Explanation

Question 23 of 50

1

Protein diseases can be caused by which of the following

Select one of the following:

  • mutations affecting the 1° structure.

  • mutations affecting the 3° structure.

  • changes in the post-synthetic processing of proteins.

  • All of the above are potential causes.

  • None of the above are potential causes

Explanation

Question 24 of 50

1

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

Select one of the following:

  • a loop region with 8 amino acids

  • a β sheet region made up of amino acids Val, Ile, Phe

  • an α helix made up of Cys, Pro, and Phe

  • a β hairpin with 12 amino acids

  • All have equal stability.

Explanation

Question 25 of 50

1

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

Select one of the following:

  • α helix and β sheet, favorable

  • α helix, unfavorable

  • β sheet, unfavorable

  • α helix, favorable

  • β sheet, favorable

Explanation

Question 26 of 50

1

A chaperonin

Select one of the following:

  • helps fold some proteins in their lowest energy state.

  • is required for all proteins to fold properly.

  • mediates the unfolding of proteins.

  • is required for protein denaturation

  • counteracts the laws of thermodynamics.

Explanation

Question 27 of 50

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?

Select one of the following:

  • It has 3.6 residues per turn.

  • It is a random coil, not a helix.

  • It is an α helix.

  • It has more residues per turn than an α helix.

  • It has fewer residues per turn than an α helix.

Explanation

Question 28 of 50

1

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

Select one of the following:

  • orientating amino acid groups to maximize hydrogen bonding

  • folding hydrophobic groups towards the exterior of the protein

  • burying polar groups towards the interior of the protein

  • extensive cavity formation

  • all of the above

Explanation

Question 29 of 50

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)?

Select one of the following:

  • aggregation of a misfolded protein

  • aggregation of random coil regions on a protein

  • ingestion of ammonium salts

  • the serious side effects of experimental treatment with Quinacrine

  • All are potential causes Creutzfeld-Jakob disease.

Explanation

Question 30 of 50

1

Proteins can denature due to a change in

Select one of the following:

  • pH

  • temperature

  • ionic strength

  • all of the above

  • none of the above

Explanation

Question 31 of 50

1

48. 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

Select one of the following:

  • “1” because Hyp has OH groups

  • “1” because the electronegativity of oxygen is greater

  • “2” because the electronegativity of proline is greater

  • “3” because Thr is a small amino acid which allows close packing

Explanation

Question 32 of 50

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

Select one of the following:

  • alpha-keratin

  • beta-keratin

  • collagen

  • pleated collagen

Explanation

Question 33 of 50

1

Which of the following structural proteins has the greatest elasticity?

Select one of the following:

  • alpha-keratin

  • beta-keratin

  • collagen

  • pleated collagen

Explanation

Question 34 of 50

1

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

Select one of the following:

  • alpha-keratin

  • collagen

  • pleated collagen

  • A and B

  • B and C

Explanation

Question 35 of 50

1

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

Select one of the following:

  • noncovalent interactions contribute to the strength of all these proteins

  • all of them consist of alpha-helix structure

  • all of them require vit C

  • decrease in amounts of any of them cause scurvy

  • all of these are true of fibrous proteins

Explanation

Question 36 of 50

1

Which 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.

Select one of the following:

  • I

  • I, II

  • I, II, III

  • II, III

  • I, III

Explanation

Question 37 of 50

1

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

Select one of the following:

  • ensure that improper aggregation of hydrophobic segments does not occur

  • engulf the protein in order to ensure that the protein is not damaged by heat denaturation

  • facilitate native folding by exposing hydrophobic segments of the protein as it is synthesized

  • facilitate aggregation of multiple subunits of a protein during synthesis

  • All of the above are accomplished by molecular chaperones.

Explanation

Question 38 of 50

1

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

Select one of the following:

  • Spontaneous refolding of proteins into their native state under physiologic conditions.

  • Assisted refolding of proteins into their native state under laboratory conditions.

  • Identification of thermostable proteins than maintain their native state in adverse temperatures.

  • A and B

  • B and C

Explanation

Question 39 of 50

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?

Select one of the following:

  • Proteins with hydrophobic groups on the interior would maintain their native state.

  • Proteins with hydrophilic groups on the exterior would denature and likely precipitate

  • Proteins with exposed hydrophobic groups would maintain their structure and remain in solution

  • Both A and B would occur.

  • Both B and C would occur.

Explanation

Question 40 of 50

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?
I. Leucine vs. Isoleucine
II. Phenylalanine vs. Alanine
III. Glutamate vs. Glutamic acid

Select one of the following:

  • Those in both groups I and II could be differentiated

  • Those in both groups I and III could be differentiated

  • Only those in group II could be differentiated

  • Only those in group III could be differentiated

  • Only those in groupI could be differentiated

Explanation

Question 41 of 50

1

The most important contribution to the stability of a protein’s conformation appears to be the:

Select one of the following:

  • entropy increase from the decrease in ordered water molecules forming a solvent shell around it.

  • maximum entropy increase from ionic interactions between the ionized amino acids in a protein.

  • sum of free energies of formation of many weak interactions among the hundreds of amino acids in a protein

  • sum of free energies of formation of many weak interactions between its polar amino acids and surrounding water

  • stabilizing effect of hydrogen bonding between the carbonyl group of one peptide bond and the amino group of another.

Explanation

Question 42 of 50

1

In 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:

Select one of the following:

  • formation of the maximum number of hydrophilic interactions.

  • maximization of ionic interactions.

  • minimization of entropy by the formation of a water solvent shell around the protein.

  • placement of hydrophobic amino acid residues within the interior of the protein.

  • placement of polar amino acid residues around the exterior of the protein.

Explanation

Question 43 of 50

1

In an alpha-helix, the R groups on the amino acid residues:

Select one of the following:

  • alternate between the outside and the inside of the helix.

  • are found on the outside of the helix spiral.

  • cause only right-handed helices to form.

  • generate the hydrogen bonds that form the helix.

  • stack within the interior of the helix.

Explanation

Question 44 of 50

1

The major reason that antiparallel beta-stranded protein structures are more stable than parallel beta-stranded structures is that the latter:

Select one of the following:

  • are in a slightly less extended configuration than antiparallel strands.

  • do not have as many disulfide crosslinks between adjacent strands.

  • do not stack in sheets as well as antiparallel strands.

  • have fewer lateral hydrogen bonds than antiparallel strands.

  • have weaker hydrogen bonds laterally between adjacent strands.

Explanation

Question 45 of 50

1

The 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:

Select one of the following:

  • always side by side

  • generally near each other in sequence

  • invariably restricted to about 7 of the 20 standard amino acids

  • often on different polypeptide strands

  • usually near the polypeptide chain’s amino terminus or carboxyl terminus

Explanation

Question 46 of 50

1

Proteins often have regions that show specific, coherent patterns of folding or function. These regions are called:

Select one of the following:

  • domains

  • oligomers

  • peptides

  • sites

  • subunits

Explanation

Question 47 of 50

1

An average protein will not be denatured by

Select one of the following:

  • a detergent such as sodium dodecyl sulfate.

  • heating to 90°C

  • iodoacetic acid

  • pH 10.

  • urea.

Explanation

Question 48 of 50

1

Which of the following is least likely to result in protein denaturation?

Select one of the following:

  • altering net charge by changing pH

  • changing the salt concentration

  • disruption of weak interactions by boiling

  • exposure to detergents

  • mixing with organic solvents such as acetone

Explanation

Question 49 of 50

1

Protein 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.

Select one of the following:

  • ligand

  • molecular chaperone

  • protein precursor

  • structural motif

  • supersecondary structural unit

Explanation

Question 50 of 50

1

Which of the following is not known to be involved in the process of assisted folding of proteins?

Select one of the following:

  • chaperonins

  • disulfide interchange

  • heat shock proteins

  • peptide bond hydrolysis

  • peptide bond isomerization

Explanation

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