Free ACT Test Exam Braindumps (page: 152)

All proteins consist of a string of amino acids linked together by peptide bonds. Because of its unique sequence of amino acids, every protein is distinct. Each protein folds into a specific conformation when manufactured by cells. All proteins must attain three-dimensional structures to properly function in the cell. While the peptide bonds between the amino acids are relatively rigid, all the other chemical bonds within a protein are flexible and can contort within certain limits. The ability of a protein to fold depends on the flexibility of these chemical bonds. A small protein of about 100 amino acids could undergo an astronomical number of trials and errors before assuming its final structure. This sampling of many conformations before attaining the right one would take far too long and so scientists hypothesize that there must be pathways which guide individual proteins to the right conformations, thereby eliminating total randomness in sampling. Three pathway models of protein folding have been proposed.

Diffusion-collision model
This model suggests that an amino acid within a protein can diffuse within its environment until it collides with its specific partner amino acid, to which it adheres. When all the amino acids, are involved in favorable interactions, the protein ceases to diffuse and the proper conformation is attained.

Nucleation model
This model postulates that the acquisition of the proper fold within several amino acids would trigger the folding process. These amino acids act as nucleation centers and cause a domino effect in promoting protein folding.

The protein can be imagined to sequentially acquire its proper conformation beginning from the nucleation centers.

Hydrophobic-collapse model
Out of the 20 different amino acids, some are hydrophobic. A hydrophobic amino acid is one that does not like to be associated with water but does like to be associated with others like itself. In the hydrophobic-collapse model, hydrophobic amino acids in the protein collapse into the center of the protein leaving the hydrophilic (water-loving) amino acids to surround them and interact with water.

A certain mutation of an amino acid, which is thought to play a major role in initiating protein folding, does not affect the general structure of the protein. Which of the proposed models cannot account for this observation?

All proteins consist of a string of amino acids linked together by peptide bonds. Because of its unique sequence of amino acids, every protein is distinct. Each protein folds into a specific conformation when manufactured by cells. All proteins must attain three-dimensional structures to properly function in the cell. While the peptide bonds between the amino acids are relatively rigid, all the other chemical bonds within a protein are flexible and can contort within certain limits. The ability of a protein to fold depends on the flexibility of these chemical bonds. A small protein of about 100 amino acids could undergo an astronomical number of trials and errors before assuming its final structure. This sampling of many conformations before attaining the right one would take far too long and so scientists hypothesize that there must be pathways which guide individual proteins to the right conformations, thereby eliminating total randomness in sampling. Three pathway models of protein folding have been proposed.

Diffusion-collision model
This model suggests that an amino acid within a protein can diffuse within its environment until it collides with its specific partner amino acid, to which it adheres. When all the amino acids, are involved in favorable interactions, the protein ceases to diffuse and the proper conformation is attained.

Nucleation model
This model postulates that the acquisition of the proper fold within several amino acids would trigger the folding process. These amino acids act as nucleation centers and cause a domino effect in promoting protein folding. The protein can be imagined to sequentially acquire its proper conformation beginning from the nucleation centers.

Hydrophobic-collapse model
Out of the 20 different amino acids, some are hydrophobic. A hydrophobic amino acid is one that does not like to be associated with water but does like to be associated with others like itself. In the hydrophobic-collapse model, hydrophobic amino acids in the protein collapse into the center of the protein leaving the hydrophilic (water-loving) amino acids to surround them and interact with water.

The nucleation model suggests that some amino acids are more important than others whereas the diffusion- collision model supposes that all amino acids are equally important. Which of the following statements is NOT true?

All proteins consist of a string of amino acids linked together by peptide bonds. Because of its unique sequence of amino acids, every protein is distinct. Each protein folds into a specific conformation when manufactured by cells. All proteins must attain three-dimensional structures to properly function in the cell. While the peptide bonds between the amino acids are relatively rigid, all the other chemical bonds within a protein are flexible and can contort within certain limits. The ability of a protein to fold depends on the flexibility of these chemical bonds. A small protein of about 100 amino acids could undergo an astronomical number of trials and errors before assuming its final structure. This sampling of many conformations before attaining the right one would take far too long and so scientists hypothesize that there must be pathways which guide individual proteins to the right conformations, thereby eliminating total randomness in sampling. Three pathway models of protein folding have been proposed.

Diffusion-collision model
This model suggests that an amino acid within a protein can diffuse within its environment until it collides with its specific partner amino acid, to which it adheres. When all the amino acids, are involved in favorable interactions, the protein ceases to diffuse and the proper conformation is attained.

Nucleation model
This model postulates that the acquisition of the proper fold within several amino acids would trigger the folding process. These amino acids act as nucleation centers and cause a domino effect in promoting protein folding. The protein can be imagined to sequentially acquire its proper conformation beginning from the nucleation centers.

Hydrophobic-collapse model
Out of the 20 different amino acids, some are hydrophobic. A hydrophobic amino acid is one that does not like to be associated with water but does like to be associated with others like itself. In the hydrophobic-collapse model, hydrophobic amino acids in the protein collapse into the center of the protein leaving the hydrophilic (water-loving) amino acids to surround them and interact with water.

Implicit in the nucleation model is the assumption that:

All proteins consist of a string of amino acids linked together by peptide bonds. Because of its unique sequence of amino acids, every protein is distinct. Each protein folds into a specific conformation when manufactured by cells. All proteins must attain three-dimensional structures to properly function in the cell. While the peptide bonds between the amino acids are relatively rigid, all the other chemical bonds within a protein are flexible and can contort within certain limits. The ability of a protein to fold depends on the flexibility of these chemical bonds. A small protein of about 100 amino acids could undergo an astronomical number of trials and errors before assuming its final structure. This sampling of many conformations before attaining the right one would take far too long and so scientists hypothesize that there must be pathways which guide individual proteins to the right conformations, thereby eliminating total randomness in sampling. Three pathway models of protein folding have been proposed.

Diffusion-collision model
This model suggests that an amino acid within a protein can diffuse within its environment until it collides with its specific partner amino acid, to which it adheres. When all the amino acids, are involved in favorable interactions, the protein ceases to diffuse and the proper conformation is attained.

Nucleation model
This model postulates that the acquisition of the proper fold within several amino acids would trigger the folding process. These amino acids act as nucleation centers and cause a domino effect in promoting protein folding. The protein can be imagined to sequentially acquire its proper conformation beginning from the nucleation centers.

Hydrophobic-collapse model
Out of the 20 different amino acids, some are hydrophobic. A hydrophobic amino acid is one that does not like to be associated with water but does like to be associated with others like itself. In the hydrophobic-collapse model, hydrophobic amino acids in the protein collapse into the center of the protein leaving the hydrophilic (water-loving) amino acids to surround them and interact with water.

A molecular chaperoning is a protein that aids small proteins in establishing their structures. The chaperoning has a barrel-like cavity that provides an unfolded protein an opportunity to fold. If the hydrophobic- collapse model can be used to explain this particular folding process, what can be said about the amino acids of the molecular chaperoning that come in contact with the unfolded protein?