Question 1

Which of the following statements best explains why proteins are considered the most functionally diverse molecules in living systems?

Accepted Answer

Proteins perform a wide variety of functions, including catalysis, structure, transport, movement, and regulation, due to their diverse amino acid sequences and structures.

Question 2

Which of the following is a correct example of a fibrous protein and its primary function?

Accepted Answer

Collagen; structural support in connective tissues

Question 3

Amino acids are classified based on the polarity of their side chains. Which of the following amino acids is correctly matched with its group?

Accepted Answer

Glutamic acid – Acidic side chain

Question 4

Which of the following best describes the structure and function of a zwitterion at physiological pH?

Accepted Answer

A molecule with a positively charged amino group ($$\mathrm{NH_3$^+}) $$and a negatively charged carboxyl group ($$\mathrm{COO^-}$$), resulting in no net charge.

Question 5

Which of the following amino acids is unique because its side chain forms a covalent bond with the amino group, resulting in a secondary amine?

Accepted Answer

Proline

Question 6

A patient is diagnosed with maple syrup urine disease. Which amino acids are most likely to accumulate due to this metabolic disorder?

Accepted Answer

Valine, Leucine, Isoleucine

Question 7

Which of the following statements about the peptide bond is correct?

Accepted Answer

It is a rigid and planar bond with partial double-bond character, usually in the trans configuration.

Question 8

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

Accepted Answer

The local folding of the polypeptide backbone into structures such as $$\alpha-$$helices and $$\beta-$$pleated sheets stabilized by hydrogen bonds.

Question 9

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

Accepted Answer

Hydrogen bonds between backbone atoms in $$\alpha-$$helices

Question 10

Hemoglobin is an example of a protein with quaternary structure. Which of the following statements about hemoglobin is correct?

Accepted Answer

It is composed of two alpha and two beta chains, each surrounding a heme group.

Question 11

Which of the following best explains why proteins are least soluble in water at their isoelectric point ($$pI$$)?

Accepted Answer

At $$pI$$, proteins have no net charge, leading to minimal electrostatic repulsion and increased aggregation.

Question 12

A mutation in the $$\beta-$$globin gene leads to sickle cell anemia. What is the specific amino acid substitution responsible for this disease?

Accepted Answer

Glutamate is replaced by valine at position 6 of the $$\beta-$$globin chain.

Question 13

Which post-translational modification is correctly matched with its amino acid and cellular location?

Accepted Answer

N-linked glycosylation; asparagine; endoplasmic reticulum

Question 14

Which of the following best describes the effect of denaturation on a protein?

Accepted Answer

It disrupts secondary and tertiary structures, leading to loss of biological activity, but leaves the primary structure intact.

Question 15

Which of the following amino acids can form disulfide bonds, and what is the significance of these bonds?

Accepted Answer

Cysteine; they stabilize the tertiary and quaternary structures of proteins.

Question 16

A solution contains an amino acid at a pH below its isoelectric point ($$pI). $$What will be the net charge on the amino acid?

Accepted Answer

Net positive charge

Question 17

Which of the following is a correct statement about the relationship between the stereochemistry of amino acids and monosaccharides in nature?

Accepted Answer

Naturally occurring amino acids have L-configuration, while monosaccharides have D-configuration.

Question 18

Which of the following best describes the difference between a dipeptide and a protein?

Accepted Answer

A dipeptide contains two amino acids joined by a peptide bond, while a protein contains at least 30–50 amino acids joined by peptide bonds.

Question 19

Which of the following clinical conditions is associated with the accumulation of misfolded proteins forming insoluble aggregates, often affecting the nervous system?

Accepted Answer

Amyloidosis

Chapter 19: Proteins – Structure, Function, and Clinical Aspects

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