Proteins：练习题

In the hierarchy of protein structure, a specific globular protein is found to contain multiple polypeptide chains. Which of the following statements correctly identifies the highest level of structure and the specific bonds that maintain the 3D conformation of its individual subunits?

The induced-fit model is an essential concept in understanding enzyme action. Which statement best describes how the interaction between an enzyme and its substrate lowers the activation energy?

A globular protein is subjected to a solution with a very high concentration of urea, which is known to disrupt hydrogen bonds. Which levels of protein structure would be directly affected by this treatment?

In the structure of proteins, different types of bonds stabilize the various levels of folding. Which type of bond is specifically responsible for the formation of \(\alpha\)-helices and \(\beta\)-pleated sheets?

Consider a protein consisting of a single polypeptide chain. If a mutation changes one amino acid in the primary structure, but the protein's function remains unchanged, which of the following is the most likely explanation?

The primary structure of a protein consists of a specific sequence of amino acids. Explain how a change in this sequence can lead to a non-functional enzyme by describing the impact on the tertiary structure and the formation of the enzyme-substrate complex.

Explain the role of hydrogen bonds, ionic bonds, and disulfide bridges in maintaining the tertiary structure of a functional enzyme.

The general structure of an amino acid contains a central carbon atom. State the chemical groups that are common to all 20 amino acids found in organisms, and explain how the R-group leads to the variety of proteins observed in nature.

A specific functional protein consists of two identical polypeptide chains, each containing 120 amino acids. During the formation of this protein from its constituent amino acids, a series of chemical reactions occur to establish its final 3D shape.

a) Calculate the total number of water molecules that are eliminated during the condensation reactions required to form the primary structure of this entire protein. (2 points)
b) A scientist treats the protein with a chemical that specifically breaks disulfide bridges but leaves hydrogen bonds and ionic bonds intact. Explain the likely effect of this treatment on the protein's tertiary structure and its subsequent quaternary structure. (3 points)
c) Describe how the induced-fit model of enzyme action differs from the lock-and-key model, and explain how the change in the shape of the active site contributes to lowering the activation energy of a reaction. (3 points)