MBC HW 9

Hydropathy value:

A measure of the combined hydrophobicity and hydrophilicity of an amino acid residue.

Which of the following pairings of an item related to protein folding and a descriptive statement about it is INCORRECT:

Heat shock proteins (Hsp) : Catalyze the formation of native disulfide bonds.

What is the probability of refolding a denatured protein to its native conformation, in which three disulfide bonds can form randomly from 6 Cys residues?

1/15.

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

1° structure can determine 3° structure.

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

2° structure

Ribonuclease A:

A protein that can rapidly renature spontaneously.

Which of the following series of amino acids is most likely to be buried in the center of a water-soluble globular protein?

Ala, Leu, Phe

Which pairs of amino acid side chains could not interact in the interior of a protein by hydrogen bonding?

Ala, Lys Correct. The side chain of Ala is unable to make a hydrogen bond.

Metal ion:

Can stabilize folded proteins, e.g. by the tetrahedral coordination of Zn2+.

Which of statements in the following list pairing a term / structure / chemical with its definition or an effect it has on protein tertiary structure is INCORRECT:

Cosmotropic agent: Denatures proteins by increasing the solubility of nonpolar groups in water (e.g.'s include urea and the guanidinium ion).

Which statement about disulfide bonds is false?

Disulfide bonds can occur between either Cys or Met residues.

Which of the following is not a disease that is caused by protein misfolding?

Down's syndrome.

Ion pairs:

Electrostatic interactions that usually occur on the surfaces of proteins.

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

Ensure that improper aggregation of hydrophobic segments does not occur.

Which one of the following sequences of five amino acids would most likely be located on the surface of a soluble globular protein?

Glu-Asn-Ser-Thr-Gln

Which of the following sequences of amino acids is most likely to be at the surface of a water-soluble globular protein?

Glu-Asp-Lys

Which treatment is least likely to cause a protein to denature?

High concentrations of salts.

Which pair of amino acid side chains could form an ion pair?

His, Asp

The short amino acid sequence shown below occurs within the longer amino acid sequence of a large protein. This specific portion of the amino acid sequence adopts an -helical conformation.............Ala-Val-Ala-Val-Ala-Val-Ala-Val-Ala-Val...............When the protein has adopted its tertiary conformation, which of the following hydrogen bonds are most likely to be formed by groups on the amino acid residues in this short segment?

Hydrogen bonds with other residues in the same -helix.

Hydrophobic effect:

In proteins, the tendency of nonpolar side chains to minimize their contacts with water.

Detergent:

Interferes with the hydrophobic interactions responsible for a protein's native structure.

Why does a decrease in pH alter/disrupt the tertiary structure of an enzyme?

It disrupts ion pairs/salt bridges.

You have been shown the detailed 3-D structure of an unknown protein. The information indicates that the protein's non-polar amino acid side chains are all exposed on the surface, whereas its polar side chains are all "buried" in the interior. What can you conclude about this protein?

It is likely to be an integral membrane protein.

Which one of the following sequences of five amino acids would most likely be located in the interior of a water soluble globular protein?

Met-Phe-Pro-Ile-Leu

Which statement is not a consequence of the hydrophobic effect?

Metal ions can function to stabilize folded proteins.

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

Orientating amino acid groups to maximize hydrogen bonding.

What is the major factor that "drives" the folding of proteins into their tertiary structure?

Placement of hydrophobic amino acid residues within the interior of the protein.

Which of the following is TRUE about prosthetic groups?

Prosthetic groups are an integral part of the three dimensional structure of the protein.

Which of the following statements about prosthetic groups is INCORRECT?

Prosthetic groups form an integral part of the secondary structure of proteins.

Which is NOT a conclusion drawn from the experiments of Christian Anfinsen about renaturation of Ribonuclease A?

Proteins are marginally stable in solution.

Which of the following does NOT support the existence of protein folding pathways?

Proteins lose entropy when they fold into a compact conformation.

Which of the following statements about quaternary structure is FALSE?

Quaternary structure is defined as the arrangement of polypeptide backbones in proteins with four subunits.

Which of the following statements about quaternary structure is TRUE?

Quaternary structure is stabilized by the same types of noncovalent interactions as tertiary structure.

Which of the following describes the entire three-dimensional structure of a single polypeptide?

Tertiary structure

What is the primary driving force in the formation of protein tertiary structure?

The exclusion of non-polar substances from aqueous solution.

In the experiment of Christian Anfinsen, which condition permitted Ribonuclease A to renature?

The presence of O2 at pH 8.0 during renaturation.

What ultimately determines the unique three dimensional structure of soluble globular proteins?

The sequence of the amino acid residues.

Hydrogen bonds:

They fine-tune tertiary structure by selecting a unique conformation among many hydrophobically-stabilized ones

What is the major role played by prosthetic groups in proteins?

They provide reactive groups not found in amino acid side chains.

Which pairs of amino acid side chains could interact in the interior of a protein only via van der Waals interactions?

Val, Leu.

A domain is:

a folded segment of polypeptide with a separate hydrophobic core.

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

aggregation of hydrophobic regions in the protein

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

disulfide bridges

Evolutionary processes have

enhanced efficient folding pathways.

A chaperonin

helps fold some proteins in their lowest energy state.

Proteins can denature due to a change in

pH. temperature. ionic strength. ALL OF THE ABOVE

In general molecular chaperone proteins function by

preventing premature folding by binding hydrophobic regions of the protein.

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

protein denaturation

Chaperonins such as the GroEL/ES system

require ATP hydrolysis.

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

scurvy