Question 1

Christian Anfinsen showed in a famous experiment that it is possible to unfold a protein and refold it to obtain a functional protein.Which two reagents were used in this experiment to unfold the protein?
A) detergent and salt
B) urea and -mercaptoethanol
C) acid and base
D) ethanol and -mercaptoethanol

Accepted Answer

Anfinsen used urea and 11ea8d43_ab6d_b417_b445_f15da46cf882_TB6697_11_TB6697_11-mercaptoethanol to unfold the protein in his experiment. Urea helps to disrupt the hydrogen bonds and other non-covalent interactions that stabilize the protein's structure, while 11ea8d43_ab6d_b417_b445_f15da46cf882_TB6697_11_TB6697_11-mercaptoethanol breaks down disulfide bonds. By removing these stabilizing forces, the protein can be unfolded and then refolded into a functional protein.

Question 2

What is a current hypothesis that explains the infectious nature of prion diseases?
A) The virus responsible for prion diseases is transmissible.
B) Unfavorable environmental factors negatively influence healthy cells.
C) The small molecule denaturants found in infected cells are passed on to healthy cells.
D) The presence of an improperly folded prion protein promotes the misfolding of normal prion proteins.

Accepted Answer

The hypothesis currently accepted to explain the infectious nature of prion diseases postulates that the presence of an improperly folded prion protein promotes the misfolding of normal prion proteins, leading to the spread of the disease. This theory suggests that prion diseases are caused by a protein rather than by a virus or another infectious agent.

Question 3

In multi-subunit proteins,such as hemoglobin,the different subunits are usually bound to one another by all of the following EXCEPT
A) hydrogen bonds.
B) electrostatic interactions.
C) hydrophobic interactions.
D) peptide bonds.

Accepted Answer

Peptide bonds join together amino acids within a single protein subunit, but they do not directly bind different subunits to each other. Instead, different subunits are typically held together by noncovalent interactions such as hydrogen bonding, electrostatic interactions, and hydrophobic interactions.

Question 4

Cells deal with misfolded proteins by
A) storing them for later energy use.
B) collecting and excreting them from the cell.
C) aggregating them to maintain the cell's structural integrity.
D) degrading them to individual amino acids.

Accepted Answer

Cells deal with misfolded proteins by degrading them to individual amino acids through a process called proteolysis. This helps maintain the proper functioning of the cell and prevents the accumulation of toxic proteins. Storing or aggregating misfolded proteins can lead to cell dysfunction and disease, so this is not typically a strategy used by cells. Excreting misfolded proteins is also not a common method of dealing with them.

Question 5

In the Anfinsen experiment with the unfolding of RNaseA,what order could the chemical reagents be removed in order to achieve an inactive protein?
A) Remove denaturant first and reductant second.
B) Simultaneously remove denaturant and reductant.
C) Remove reductant first, denaturant second, and then finally add back reductant.
D) Remove reductant first and denaturant second.

Accepted Answer

In the Anfinsen experiment, removing the reductant first and denaturant second is the best choice as this would result in the protein being left in its oxidized, disulfide-bonded inactive form. This is because the disulfide bonds are formed between cysteine residues in a protein via oxidation, and the reducing agent would have been used to break these bonds and disrupt the protein structure. Removing the denaturant alone would not be sufficient to inactivate the protein. Similarly, simultaneous removal of both denaturant and reductant may not yield the same result as sequential removal. Finally, adding back the reductant after removing both the denaturant and reductant would only serve to activate the protein again by breaking the disulfide bonds.

Question 6

Draw the structure of the amino acid glutamate showing the predominant form found at pH 7.0 (assume NH₃₊ pKa 9.0; Glu pK_R 4.0; COOH pKa 2.0).

Accepted Answer

The answer of Draw the structure of the amino acid...

Question 7

Calculate the pI for the following dipeptide using the pKas shown.

Accepted Answer

The answer of Calculate the pI for the following dipeptide...

Question 8

The following amino acid is discovered in a newly isolated protein.What would it be called,and does it represent a new amino acid?

Accepted Answer

The answer of The following amino acid is discovered in...

Question 9

The essential amino acids in adult humans are those that are required in our diet because of a lack of the biosynthetic pathway in our cells.The single-letter abbreviations for these amino acids are WVMILKFHT.Name these amino acids.

Accepted Answer

The answer of The essential amino acids in adult humans...

Question 10

At the interface between subunits of a protein with quaternary structure,which of the following interactions between amino acid side chains would contribute to the stability of the dimer?
A) glutamate-aspartate.
B) leucine-aspartate.
C) glutamate-lysine.
D) phenylalaninelysine.

Accepted Answer

Glutamate and lysine can form a salt bridge due to the attraction between the negatively charged side chain of glutamate and the positively charged side chain of lysine, contributing to the stability of the protein dimer.

Question 11

Shown is the titration curve for the amino acid aspartic acid.Draw the predominant protonation state of aspartic acid found at point A in the curve.

Accepted Answer

The answer of Shown is the titration curve for the...

Question 12

Of the three proposed models of globular protein folding,which one describes formation of an initial disordered protein interior,followed next by ordering of secondary and tertiary structures?
A) mutant globule
B) hydrophobic collapse model
C) framework model
D) nucleation model

Accepted Answer

The hydrophobic collapse model suggests that folding begins with the collapse of the protein's hydrophobic core, resulting in an initially disordered interior. The secondary and tertiary structures then form as the polar residues are forced to the surface and form stabilizing interactions with water molecules. The other models do not describe this specific sequence of events.

Question 13

Cystic fibrosis results from the misfolding of proteins that never get the chance to properly insert into the membranes of lung epithelial cells and perform their function.This is generally referred to as a __________ disease.
A) loss-of-function protein folding
B) chaperonin-unassisted folding
C) gain-of-function protein folding
D) amyloid plaque-forming

Accepted Answer

Cystic fibrosis is a classic example of a loss-of-function protein folding disease because the misfolded proteins do not properly insert into the lung epithelial cell membranes and perform their normal function, ultimately leading to the disease phenotype.

Question 14

It is important for cells to degrade misfolded proteins.If misfolded proteins are not degraded,the misfolded proteins may
A) waste excessive ATP in attempts to refold them.
B) aggregate and interfere with normal cellular function.
C) eventually refold, but not until excessive and sometimes fatal levels of cellular energy are spent.
D) be excreted from the cell rather than recycled for building blocks.

Accepted Answer

Misfolded proteins can aggregate and interfere with normal cellular function if they are not degraded. This can lead to diseases such as Alzheimer's and Parkinson's. Wasting excessive ATP in attempts to refold them (A) and spending excessive and sometimes fatal levels of cellular energy to refold them (C) are also possible consequences, but the primary concern is the interference with cellular function. Excreting the misfolded proteins from the cell (D) is not a viable option as it does not address the underlying issue of misfolded proteins and can lead to a loss of important building blocks for the cell.

Question 15

Of the three proposed models of globular protein folding,which one describes the initial formation of all secondary structures,followed by the arrangement of those secondary structures into a final tertiary structure?
A) mutant globule
B) hydrophobic collapse model
C) framework model
D) nucleation model

Accepted Answer

The framework model describes protein folding as the initial formation of secondary structures, which then arrange into the final tertiary structure.

Question 16

Which of the following statements about the clamp-type chaperone protein Hsp70 is correct?
A) Hsp70 uses ATP binding and hydrolysis energy to assist in the folding of a protein.
B) Hsp70 is a multi-subunit protein shaped like a large barrel, inside of which the folding protein is protected.
C) Hsp70 is most active during cell division phases.
D) Hsp70 assists in protein unfolding by hydrolyzing and remaking the protein peptide bonds.

Accepted Answer

Hsp70 uses ATP binding and hydrolysis energy to assist in the folding of a protein. It binds to exposed hydrophobic regions of the substrate protein, preventing aggregation and facilitating proper folding. The ATP-dependent cycle of binding and release helps to drive the folding reaction. None of the other answer choices accurately describe Hsp70.

Question 17

What is the difference between clamp-type and chamber-type chaperone proteins?
A) One uses ATP and the other does not.
B) One folds proteins, whereas the other just protects them from unfolding.
C) They are shaped differently.
D) One type is found extracellularly and one intracellularly.

Accepted Answer

Clamp-type and chamber-type chaperone proteins differ in their structure; clamp-type chaperones have a clamp-like shape, while chamber-type chaperones have a chamber-like structure.

Question 18

Which of the following statements about the chamber-type chaperone protein GroEL-GroES is correct?
A) GroEL-GroES requires the hydrolysis of multiple ATPs to assist in the folding of a protein.
B) GroEL-GroES recycles misfolded proteins by recovering individual amino acids.
C) GroEL-GroES assists in protein unfolding by hydrolyzing and remaking the protein peptide bonds.
D) GroEL-GroES uses GroEL as a cap, trapping an unfolded protein in the GroES chamber.

Accepted Answer

GroEL-GroES requires the hydrolysis of multiple ATPs to assist in the folding of a protein by providing the energy needed for conformational changes that facilitate proper protein folding.

Question 19

Which gives rise to a favorable enthalpic (  S)driving force for protein folding?
A) The lining up of hydrogen bonds as the protein folds.
B) The limiting of possible conformations as the protein folds.
C) The decrease in ordered water molecules as hydrophobic amino acids pack together.
D) The stabilization caused by favorable electrostatic interactions of amino acid side chains.

Accepted Answer

The decrease in ordered water molecules as hydrophobic amino acids pack together gives rise to a favorable enthalpic driving force for protein folding. This is because the hydrophobic effect drives hydrophobic molecules (like hydrophobic amino acids) together in aqueous environments, minimizing contact with ordered water molecules, which increases entropy and is energetically favorable. This enthalpic driving force is in addition to entropy-driven forces that arise from limiting the possible conformations (choice B) as the protein folds. The lining up of hydrogen bonds (choice A) and stabilization caused by favorable electrostatic interactions of amino acid side chains (choice D) are also important driving forces for protein folding but do not necessarily give rise to a favorable enthalpic driving force.

Question 20

What is believed to be the underlying cause of prion protein plaque formation? A) The PrP^Sc proteins are misfolded and aggregated from PrP^c proteins. B) The unstructured N-terminal region of PrP^c is thought to remain unfolded. C) The normal PrP^c proteins are aggregated. D) The PrP^Sc protein adheres to and inhibits cell membranes.

Accepted Answer

The misfolding and aggregation of PrP^c proteins into PrP^Sc proteins is believed to be the underlying cause of prion protein plaque formation.

Quiz 4: Protein Structure

Christian Anfinsen showed in a famous experiment that it is possible to unfold a protein and refold it to obtain a functional protein.Which two reagents were used in this experiment to unfold the protein?

What is a current hypothesis that explains the infectious nature of prion diseases?

In multi-subunit proteins,such as hemoglobin,the different subunits are usually bound to one another by all of the following EXCEPT

Cells deal with misfolded proteins by

In the Anfinsen experiment with the unfolding of RNaseA,what order could the chemical reagents be removed in order to achieve an inactive protein?

Draw the structure of the amino acid glutamate showing the predominant form found at pH 7.0 (assume NH₃₊ pKa 9.0; Glu pK_R 4.0; COOH pKa 2.0).

Calculate the pI for the following dipeptide using the pKas shown.

The following amino acid is discovered in a newly isolated protein.What would it be called,and does it represent a new amino acid?

The essential amino acids in adult humans are those that are required in our diet because of a lack of the biosynthetic pathway in our cells.The single-letter abbreviations for these amino acids are WVMILKFHT.Name these amino acids.

At the interface between subunits of a protein with quaternary structure,which of the following interactions between amino acid side chains would contribute to the stability of the dimer?

Shown is the titration curve for the amino acid aspartic acid.Draw the predominant protonation state of aspartic acid found at point A in the curve.

Of the three proposed models of globular protein folding,which one describes formation of an initial disordered protein interior,followed next by ordering of secondary and tertiary structures?

Cystic fibrosis results from the misfolding of proteins that never get the chance to properly insert into the membranes of lung epithelial cells and perform their function.This is generally referred to as a __________ disease.

It is important for cells to degrade misfolded proteins.If misfolded proteins are not degraded,the misfolded proteins may

Of the three proposed models of globular protein folding,which one describes the initial formation of all secondary structures,followed by the arrangement of those secondary structures into a final tertiary structure?

Which of the following statements about the clamp-type chaperone protein Hsp70 is correct?

What is the difference between clamp-type and chamber-type chaperone proteins?

Which of the following statements about the chamber-type chaperone protein GroEL-GroES is correct?

Which gives rise to a favorable enthalpic ( S) driving force for protein folding?

What is believed to be the underlying cause of prion protein plaque formation?

Quiz 4: Protein Structure

Christian Anfinsen showed in a famous experiment that it is possible to unfold a protein and refold it to obtain a functional protein.Which two reagents were used in this experiment to unfold the protein?

What is a current hypothesis that explains the infectious nature of prion diseases?

In multi-subunit proteins,such as hemoglobin,the different subunits are usually bound to one another by all of the following EXCEPT

Cells deal with misfolded proteins by

In the Anfinsen experiment with the unfolding of RNaseA,what order could the chemical reagents be removed in order to achieve an inactive protein?

Draw the structure of the amino acid glutamate showing the predominant form found at pH 7.0 (assume NH3+ pKa 9.0; Glu pKR 4.0; COOH pKa 2.0).

Calculate the pI for the following dipeptide using the pKas shown.

The following amino acid is discovered in a newly isolated protein.What would it be called,and does it represent a new amino acid?

The essential amino acids in adult humans are those that are required in our diet because of a lack of the biosynthetic pathway in our cells.The single-letter abbreviations for these amino acids are WVMILKFHT.Name these amino acids.

At the interface between subunits of a protein with quaternary structure,which of the following interactions between amino acid side chains would contribute to the stability of the dimer?

Shown is the titration curve for the amino acid aspartic acid.Draw the predominant protonation state of aspartic acid found at point A in the curve.

Of the three proposed models of globular protein folding,which one describes formation of an initial disordered protein interior,followed next by ordering of secondary and tertiary structures?

Cystic fibrosis results from the misfolding of proteins that never get the chance to properly insert into the membranes of lung epithelial cells and perform their function.This is generally referred to as a __________ disease.

It is important for cells to degrade misfolded proteins.If misfolded proteins are not degraded,the misfolded proteins may

Of the three proposed models of globular protein folding,which one describes the initial formation of all secondary structures,followed by the arrangement of those secondary structures into a final tertiary structure?

Which of the following statements about the clamp-type chaperone protein Hsp70 is correct?

What is the difference between clamp-type and chamber-type chaperone proteins?

Which of the following statements about the chamber-type chaperone protein GroEL-GroES is correct?

Which gives rise to a favorable enthalpic ( S) driving force for protein folding?

What is believed to be the underlying cause of prion protein plaque formation?

Draw the structure of the amino acid glutamate showing the predominant form found at pH 7.0 (assume NH₃₊ pKa 9.0; Glu pK_R 4.0; COOH pKa 2.0).