Question 1

Which of the following best describes the primary structure of a protein?

Accepted Answer

The sequence of amino acids in a polypeptide chain held together by peptide bonds.

Question 2

What type of bonding is primarily responsible for the formation of an alpha helix in the secondary structure of proteins?

Accepted Answer

Hydrogen bonds between the oxygen of the $\mathrm{C}=\mathrm{O}$ group and the hydrogen of the $\mathrm{N}-\mathrm{H}$ group in the next turn.

Question 3

A patient with Alzheimer's disease has beta-amyloid proteins in the brain that have changed from their normal structure. What is the structural change that occurs?

Accepted Answer

Alpha helices become sticky beta-pleated sheets, forming insoluble plaques.

Question 4

Which interaction is responsible for stabilizing the tertiary structure of a protein by forming a covalent bond between two cysteine residues?

Accepted Answer

Disulfide bond ($\mathrm{S}-\mathrm{S}$)

Question 5

Which of the following is a real-world example of protein denaturation?

Accepted Answer

The formation of a scab on a burn after applying tannic acid.

Question 6

Which of the following interactions is NOT involved in stabilizing the tertiary structure of proteins?

Accepted Answer

Peptide bonds

Question 7

Sickle-cell anemia is caused by a mutation in hemoglobin. What is the specific amino acid substitution that leads to this disease?

Accepted Answer

Glutamic acid (polar) is replaced by valine (nonpolar) in the $\beta$-chain.

Question 8

Which of the following best describes a beta-pleated sheet in protein secondary structure?

Accepted Answer

Polypeptide chains held side by side by hydrogen bonds between carbonyl oxygen and amide hydrogen atoms.

Question 9

Which type of tertiary interaction occurs between the $\mathrm{NH}_4^+$ group of a basic amino acid and the $\mathrm{COO}^-$ group of an acidic amino acid?

Accepted Answer

Salt bridge (ionic bond)

Question 10

Which structural level of protein is directly affected when heat causes the disruption of hydrogen bonds and hydrophobic interactions?

Accepted Answer

Secondary, tertiary, and quaternary structures

Question 11

Hemoglobin is an example of a protein with quaternary structure. What is the minimum number of polypeptide chains required for a protein to have quaternary structure?

Accepted Answer

Two

Question 12

Which of the following agents can cause denaturation of proteins by reacting with $\mathrm{S}-\mathrm{S}$ bonds?

Accepted Answer

Heavy metal ions such as $\mathrm{Ag}^+$, $\mathrm{Pb}^{2+}$, and $\mathrm{Hg}^{2+}$

Question 13

Which of the following is a correct match between protein structure and its description?

Accepted Answer

Secondary structure: Beta-pleated sheet formed by hydrogen bonds

Question 14

Which type of tertiary interaction is most likely to occur between two nonpolar amino acids?

Accepted Answer

Hydrophobic interaction

Question 15

A protein is exposed to agitation, such as whipping, which causes it to lose its native structure. What is the term for this process?

Accepted Answer

Denaturation

Question 16

Which of the following is a consequence of the abnormal hemoglobin structure in sickle-cell anemia?

Accepted Answer

Red blood cells become crescent-shaped and clog capillaries.

Question 17

Which of the following is NOT a type of interaction that stabilizes the quaternary structure of proteins?

Accepted Answer

Peptide bonds between subunits

Question 18

Which protein structure level is directly responsible for the biological activity of enzymes and antibodies?

Accepted Answer

Tertiary structure

Question 19

Which of the following best explains why boiling an egg causes it to harden?

Accepted Answer

Heat causes denaturation, breaking hydrogen bonds and hydrophobic interactions in the protein's tertiary structure.

Question 20

Which of the following statements about protein structural levels is correct?

Accepted Answer

Quaternary structure is the combination of two or more protein subunits stabilized by the same interactions as tertiary structure.

Protein Structure: Primary, Secondary, Tertiary, and Quaternary Levels, and Denaturation

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