Question 1

Which of the following best describes the structure of an amino acid found in human proteins?

Accepted Answer

A central carbon atom bonded to an amino group (NH2), a carboxyl group (COOH), a hydrogen atom, and a variable R-side chain.

Question 2

At physiological pH (around 7.4), most amino acids exist as zwitterions. Which of the following best describes a zwitterion?

Accepted Answer

A molecule with both a positive and a negative charge, but overall neutral.

Question 3

Which of the following statements about the stereochemistry of amino acids in human proteins is correct?

Accepted Answer

Only L-amino acids are incorporated into human proteins.

Question 4

Which of the following best explains why amino acids are excellent buffers in biological systems?

Accepted Answer

They contain both acidic (COOH/COO−) and basic (NH2/NH3+) groups that can donate or accept protons depending on the pH.

Question 5

A patient with sickle-cell anemia has a single amino acid substitution in the β-chain of hemoglobin. Which level of protein structure is directly altered by this mutation?

Accepted Answer

Primary structure

Question 6

Which of the following bonds is responsible for stabilizing the α-helix structure in proteins?

Accepted Answer

Hydrogen bonds between the N-H and C=O groups of the peptide backbone.

Question 7

Which of the following treatments would most likely disrupt the hydrophobic interactions in a protein, leading to denaturation?

Accepted Answer

Heating the protein above its optimal temperature.

Question 8

A protein is hydrolyzed in the stomach by the enzyme pepsin. What is the chemical result of this hydrolysis?

Accepted Answer

The peptide bonds are broken, resulting in smaller peptides and free amino acids.

Question 9

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

Accepted Answer

The arrangement and interaction of multiple polypeptide subunits.

Question 10

A newborn is diagnosed with Maple Syrup Urine Disease (MSUD) due to a defect in the breakdown of branched-chain amino acids. Which amino acids are primarily affected?

Accepted Answer

Leucine, isoleucine, and valine

Question 11

Which of the following is a real-life example of how a single amino acid change can lead to disease?

Accepted Answer

A mutation in the β-globin gene causing sickle-cell anemia.

Question 12

Which of the following best explains why changes in body temperature or pH can be detrimental to protein function?

Accepted Answer

They disrupt non-covalent interactions that maintain protein structure, leading to denaturation.

Question 13

Which of the following is NOT a function of proteins in the human body?

Accepted Answer

Energy storage as the main long-term reserve

Question 14

Which of the following best describes the process of forming a peptide bond between two amino acids?

Accepted Answer

A condensation reaction where a molecule of water is removed.

Question 15

Which of the following statements about immunoglobulins is correct?

Accepted Answer

They are proteins involved in defence, and their antigen-binding sites are determined by their amino acid sequence.

Question 16

A patient presents with symptoms of phenylketonuria (PKU). Which enzyme is most likely deficient, and what is the consequence?

Accepted Answer

Phenylalanine hydroxylase; inability to convert phenylalanine to tyrosine.

Question 17

Which of the following best explains why leucine, isoleucine, and valine are affected by the same enzyme defect in MSUD?

Accepted Answer

They all have similar branched-chain R-groups and are substrates for the same enzyme.

Question 18

Which of the following is a correct statement about the isoelectric point ($$pI) of an $$amino acid?

Accepted Answer

At $$pH = pI$$, the amino acid exists as a zwitterion with no net charge.

Question 19

Which of the following best describes the role of disulfide bonds in protein structure?

Accepted Answer

They are covalent bonds that stabilize tertiary and quaternary structures.

Amino Acids and Proteins: Structure, Function, and Clinical Relevance

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