Question 1

Which of the following best describes the secondary structure of proteins?

Accepted Answer

Local areas of repeating polypeptide chain structure stabilized by hydrogen bonds.

Question 2

Which statement about the rotation around bonds in a polypeptide backbone is correct?

Accepted Answer

Rotation is only allowed around the bonds adjacent to the alpha carbon, described by the angles $$\phi$$ and $$\psi.$$

Question 3

Which of the following is a correct description of the Ramachandran plot?

Accepted Answer

It displays the sterically allowed values of $$\phi$$ and $$\psi$$ angles for polypeptides.

Question 4

Which of the following secondary structures is stabilized by hydrogen bonds nearly parallel to the helix axis?

Accepted Answer

Right-handed $$\alpha-$$helix

Question 5

Collagen is unique among proteins because it contains which of the following modified amino acids?

Accepted Answer

Hydroxyproline and hydroxylysine

Question 6

A deficiency in vitamin C (ascorbic acid) leads to which of the following effects on collagen?

Accepted Answer

Impaired hydroxylation of proline residues, resulting in weakened collagen and symptoms of scurvy

Question 7

Which of the following statements about globular proteins is correct?

Accepted Answer

They have a nonpolar (hydrophobic) interior and a hydrophilic exterior.

Question 8

Which thermodynamic equation describes the free energy change associated with protein folding?

Accepted Answer

$$\Delta G = \Delta H - T\Delta S$$

Question 9

Disulfide bonds contribute to protein stability primarily by:

Accepted Answer

Reducing the number of conformations possible in the unfolded state, thus decreasing entropy.

Question 10

Which of the following best explains the 'hydrophobic effect' in protein folding?

Accepted Answer

Hydrophobic side chains cluster in the protein interior, releasing ordered water molecules and increasing solvent entropy.

Question 11

Which of the following is a function of molecular chaperones in cells?

Accepted Answer

They prevent intermolecular interactions that lead to protein aggregation, especially under stress conditions.

Question 12

Which protein folding disease is associated with amyloid $$\beta$$ peptide aggregation?

Accepted Answer

Alzheimer's disease

Question 13

Which experimental technique is commonly used to estimate the number and molecular masses of protein subunits under denaturing conditions?

Accepted Answer

SDS-PAGE (sodium dodecyl sulfate polyacrylamide gel electrophoresis)

Question 14

A protein domain is best defined as:

Accepted Answer

A compact, independently folding unit within a larger protein, often with a specific function.

Question 15

Which of the following statements about $$\beta-$$sheets is correct?

Accepted Answer

Hydrogen bonds in $$\beta-$$sheets are formed between adjacent $$\beta-$$strands and stabilize the sheet.

Question 16

Which of the following is a characteristic of fibrous proteins such as keratin?

Accepted Answer

They have elongated molecules with well-defined secondary structures.

Question 17

Which of the following is true regarding the folding pathway of a protein?

Accepted Answer

Protein folding often involves intermediate states and can be represented as a funnel-shaped energy landscape.

Question 18

Which of the following interactions is NOT a major contributor to the stabilization of protein tertiary structure?

Accepted Answer

Covalent bonds between all amino acid side chains

Question 19

Which of the following best describes quaternary structure in proteins?

Accepted Answer

The spatial arrangement of multiple polypeptide chains to form multisubunit complexes.

The Three-Dimensional Structure of Proteins

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