Question 1

An  α\alphaα helix would be destabilized most by:

Accepted Answer

A)  an electric dipole spanning several peptide bonds throughout the  α\alphaα  helix.
B)  interactions between neighboring Asp and Arg residues.
C)  interactions between two adjacent hydrophobic Val residues.
D)  the presence of an Arg residue near the carboxyl terminus of the  α\alphaα  helix.
E)  the presence of two Lys residues near the amino terminus of the  α\alphaα  helix. F) A) and C)
G) C) and D)

Question 2

Why is silk fibroin so strong,but at the same time so soft and flexible?

Accepted Answer

Unlike collagen and keratin,silk fibroin...

Question 3

Pauling and Corey's studies of the peptide bond showed that:

Accepted Answer

A)  at pH 7,many different peptide bond conformations are equally probable.
B)  peptide bonds are essentially planar,with no rotation about the C-N axis.
C)  peptide bonds in proteins are unusual,and unlike those in small model compounds.
D)  peptide bond structure is extraordinarily complex.
E)  primary structure of all proteins is similar,although the secondary and tertiary structure may differ greatly.F) D) and E)
G) B) and D)

Question 4

Proteins often have regions that can fold and function as an independent entity from the whole protein.These regions are called:

Accepted Answer

A)  domains.
B)  oligomers.
C)  peptides.
D)  sites.
E)  subunits.F) A) and C)
G) A) and B)

Question 5

What are two mechanisms by which "chaperone" proteins assist in the correct folding of polypeptides?

Accepted Answer

Chaperones protect unfolded po...

Question 6

Explain (succinctly)the theoretical and/or experimental arguments in support of this statement: "The primary sequence of a protein determines its three-dimensional shape and thus its function."

Accepted Answer

Anfinsen showed that a complet...

Question 7

Thr and/or Leu residues tend to disrupt an  α\alphaα  helix when they occur next to each other in a protein because:

Accepted Answer

A)  an amino acids like Thr is highly hydrophobic.
B)  covalent interactions may occur between the Thr side chains.
C)  electrostatic repulsion occurs between the Thr side chains.
D)  steric hindrance occurs between the bulky Thr side chains.
E)  the R group of Thr can form a hydrogen bond. F) B) and E)
G) B) and D)

Question 8

Experiments on denaturation and renaturation after the reduction and reoxidation of the -S-S- bonds in the enzyme ribonuclease (RNase) have shown that:

Accepted Answer

A)  folding of denatured RNase into the native,active conformation,requires the input of energy in the form of heat.
B)  native ribonuclease does not have a unique secondary and tertiary structure.
C)  the completely unfolded enzyme,with all -S-S- bonds broken,is still enzymatically active.
D)  the enzyme,dissolved in water,is thermodynamically stable relative to the mixture of amino acids whose residues are contained in RNase.
E)  the primary sequence of RNase is sufficient to determine its specific secondary and tertiary structure.F) A) and D)
G) B) and E)

Question 9

Describe three of the important features of a $\beta$ sheet polypeptide structure.Provide one or two sentences for each feature.

Accepted Answer

In the <img  loading="lazy" src="/assets/images/blured-textbook.svg" class="d-inline m-1" alt="blured image" width="139" height="30"> sheet structure,several extended...

Question 10

Which of the following is not an appropriate description for van der Waals interactions?

Accepted Answer

A)  They involve dipole-dipole interactions.
B)  Their strength depends on the distance between the two interacting atoms.
C)  They are highly specific.
D)  An individual van der Waals interaction does not contribute significantly to the stability of a protein.
E)  They can involve hydrophobic amino acids.F) B) and E)
G) None of the above

Question 11

Which of the following statements concerning protein domains is true?

Accepted Answer

A)  They are a form of secondary structure.
B)  They are examples of structural motifs.
C)  They consist of separate polypeptide chains (subunits) .
D)  They have been found only in prokaryotic proteins.
E)  They may retain their correct shape even when separated from the rest of the protein.F) A) and B)
G) B) and E)

Question 12

What is typically found in the interior of a water-soluble globular protein?

Accepted Answer

Hydrophobic amino acid residues cluster ...

Question 13

Each of the following reagents or conditions will denature a protein.For each,describe in one or two sentences what the reagent/condition does to destroy native protein structure.
(a)urea
(b)high temperature
(c)detergent
(d)low pH

Accepted Answer

(a)Urea acts primarily by disrupting hyd...

Question 14

Describe a reservation about the use of x-ray crystallography in determining the three-dimensional structures of biological molecules.

Accepted Answer

To obtain an x-ray picture of a biomolec...

Question 15

Any given protein is characterized by a unique amino acid sequence (primary structure)and three-dimensional (tertiary)structure.How are these related?

Accepted Answer

The three-dimensional structure is deter...

Question 16

In superhelical proteins,such as collagen,several polypeptide helices are intertwined.What is the function of this superhelical twisting?

Accepted Answer

The superhelical twisting of m...

Question 17

Which of the following statements concerning the process of spontaneous folding of proteins is false?

Accepted Answer

A)  It may be an essentially random process.
B)  It may be defective in some human diseases.
C)  It may involve a gradually decreasing range of conformational species.
D)  It may involve initial formation of a highly compact state.
E)  It may involve initial formation of local secondary structure.F) A) and D)
G) A) and B)

Question 18

An average protein will not be denatured by:

Accepted Answer

A)  a detergent such as sodium dodecyl sulfate.
B)  heating to 90°C.
C)  iodoacetic acid.
D)  pH 10.
E)  urea.F) C) and D)
G) A) and E)

Question 19

A sequence of amino acids in a certain protein is found to be -Ser-Gly-Pro-Gly-.The sequence is most probably part of a(n) :

Accepted Answer

A)  antiparallel  β\betaβ  sheet.
B)  parallel  β\betaβ  sheet.
C)  ( α\alphaα  helix.) 
D)  ( α\alphaα  sheet.) 
E)  ( β\betaβ turn.)  F) B) and E)
G) B) and D)

Question 20

How can changes in pH alter the conformation of a protein?

Accepted Answer

Changes in pH can influence the extent t...

Exam 4: The Three-Dimensional Structure of Proteins

Why is silk fibroin so strong,but at the same time so soft and flexible?

Correct AnswerverifiedUnlike collagen and keratin,silk fibroin...View AnswerShow Answer

Experiments on denaturation and renaturation after the reduction and reoxidation of the -S-S- bonds in the enzyme ribonuclease (RNase) have shown that:

Correct AnswerverifiedShow Answer

Which of the following is not an appropriate description for van der Waals interactions?

Correct AnswerverifiedShow Answer

Proteins often have regions that can fold and function as an independent entity from the whole protein.These regions are called:

Correct AnswerverifiedShow Answer

Describe three of the important features of a β\betaβ sheet polypeptide structure.Provide one or two sentences for each feature.

Correct AnswerverifiedIn the sheet structure,several extended...View AnswerShow Answer

An average protein will not be denatured by:

Correct AnswerverifiedShow Answer

Thr and/or Leu residues tend to disrupt an α\alphaα helix when they occur next to each other in a protein because:

Correct AnswerverifiedShow Answer

Describe a reservation about the use of x-ray crystallography in determining the three-dimensional structures of biological molecules.

Correct AnswerverifiedTo obtain an x-ray picture of a biomolec...View AnswerShow Answer

A sequence of amino acids in a certain protein is found to be -Ser-Gly-Pro-Gly-.The sequence is most probably part of a(n) :

Correct AnswerverifiedShow Answer

Which of the following statements concerning the process of spontaneous folding of proteins is false?

Correct AnswerverifiedShow Answer

Which of the following statements concerning protein domains is true?

Correct AnswerverifiedShow Answer

Each of the following reagents or conditions will denature a protein.For each,describe in one or two sentences what the reagent/condition does to destroy native protein structure. (a)urea (b)high temperature (c)detergent (d)low pH

Correct Answerverified(a)Urea acts primarily by disrupting hyd...View AnswerShow Answer

What is typically found in the interior of a water-soluble globular protein?

Correct AnswerverifiedHydrophobic amino acid residues cluster ...View AnswerShow Answer

An α\alphaα helix would be destabilized most by:

Correct AnswerverifiedShow Answer

Explain (succinctly)the theoretical and/or experimental arguments in support of this statement: "The primary sequence of a protein determines its three-dimensional shape and thus its function."

Correct AnswerverifiedAnfinsen showed that a complet...View AnswerShow Answer

Pauling and Corey's studies of the peptide bond showed that:

Correct AnswerverifiedShow Answer

In superhelical proteins,such as collagen,several polypeptide helices are intertwined.What is the function of this superhelical twisting?

Correct AnswerverifiedThe superhelical twisting of m...View AnswerShow Answer

Any given protein is characterized by a unique amino acid sequence (primary structure)and three-dimensional (tertiary)structure.How are these related?

Correct AnswerverifiedThe three-dimensional structure is deter...View AnswerShow Answer

How can changes in pH alter the conformation of a protein?

Correct AnswerverifiedChanges in pH can influence the extent t...View AnswerShow Answer

What are two mechanisms by which "chaperone" proteins assist in the correct folding of polypeptides?

Correct AnswerverifiedChaperones protect unfolded po...View AnswerShow Answer

Correct Answer
verified
Unlike collagen and keratin,silk fibroin...
View Answer

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Describe three of the important features of a $\beta$ sheet polypeptide structure.Provide one or two sentences for each feature.

Correct Answer
verified
In the sheet structure,several extended...
View Answer

Correct Answer
verified

Thr and/or Leu residues tend to disrupt an $\alpha$ helix when they occur next to each other in a protein because:

Correct Answer
verified

Correct Answer
verified
To obtain an x-ray picture of a biomolec...
View Answer

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified
(a)Urea acts primarily by disrupting hyd...
View Answer

Correct Answer
verified
Hydrophobic amino acid residues cluster ...
View Answer

An $\alpha$ helix would be destabilized most by:

Correct Answer
verified

Correct Answer
verified
Anfinsen showed that a complet...
View Answer

Correct Answer
verified

Correct Answer
verified
The superhelical twisting of m...
View Answer

Correct Answer
verified
The three-dimensional structure is deter...
View Answer

Correct Answer
verified
Changes in pH can influence the extent t...
View Answer

Correct Answer
verified
Chaperones protect unfolded po...
View Answer