$$\text{pH} = -\log_{10}[\text{H}^+]$$

Question 1

Which of the following statements best explains why water is considered the 'universal solvent' in biological systems?

Accepted Answer

Water's polarity allows it to surround and stabilize ionic and polar solutes, keeping them in solution.

Question 2

A patient presents with a blood pH of 7.28. Which acid-base disorder is most likely present, and what is the physiological consequence?

Accepted Answer

Acidosis; disruption of protein structure and impaired cellular function.

Question 3

Which equation correctly represents the relationship between hydrogen ion concentration and pH?

Accepted Answer

$$	ext{pH} = -\log_{10}[	ext{H}^+]$$

Question 4

Which of the following best describes the structural difference between L-amino acids and D-amino acids?

Accepted Answer

L-amino acids are incorporated into human proteins, while D-amino acids are rare and found in some bacterial products.

Question 5

Amino acids act as excellent buffers in biological systems. Which property allows them to resist changes in pH?

Accepted Answer

They can both accept and donate hydrogen ions due to their amino and carboxyl groups.

Question 6

Which of the following best describes the effect of increasing substrate concentration in the presence of a competitive inhibitor?

Accepted Answer

The reaction rate increases as the substrate outcompetes the inhibitor for the active site.

Question 7

Which enzyme class catalyzes the joining of two molecules using energy from ATP, and what is a classic example?

Accepted Answer

Ligases; DNA ligase

Question 8

A mutation in the phenylalanine hydroxylase enzyme prevents the conversion of phenylalanine to tyrosine. What is the most likely outcome?

Accepted Answer

Accumulation of phenylalanine in the blood, causing intellectual disability if untreated.

Question 9

Which of the following statements about protein denaturation is correct?

Accepted Answer

Denaturation disrupts non-covalent interactions, altering secondary, tertiary, and quaternary structures but not the primary structure.

Question 10

Which of the following is a correct description of a zymogen?

Accepted Answer

A zymogen is an inactive enzyme precursor that is activated by proteolytic cleavage.

Question 11

Which of the following best explains the physiological importance of maintaining plasma pH within the range of 7.35–7.45?

Accepted Answer

It maintains optimal protein structure, enzyme activity, ion transport, and cellular metabolism.

Question 12

Which of the following is NOT a property shared by all biomolecules?

Accepted Answer

They exist only in non-isomeric forms.

Question 13

Which of the following best describes the induced-fit model of enzyme-substrate interaction?

Accepted Answer

The enzyme's active site changes shape to better fit the substrate, stabilizing the transition state.

Question 14

Which of the following is a major intracellular cation, and what is its primary role?

Accepted Answer

Potassium (K⁺); maintains electrical potential and osmotic balance inside cells.

Question 15

Which of the following best describes the effect of non-competitive reversible inhibition on enzyme activity?

Accepted Answer

The inhibitor binds to an allosteric site, altering the enzyme's shape and reducing activity regardless of substrate concentration.

Question 16

Which of the following is a correct sequence for the formation of a peptide bond between two amino acids?

Accepted Answer

Condensation reaction removes water, joining the carboxyl group of one amino acid to the amino group of another.

Question 17

Which of the following is a real-life example of the importance of protein structure in determining function?

Accepted Answer

A single amino acid substitution in haemoglobin exposes hydrophobic regions, causing sickle-cell anaemia.

Question 18

Which of the following best describes the effect of temperature on enzyme activity in humans?

Accepted Answer

Enzyme activity increases with temperature up to an optimum (around 37°C), then decreases rapidly due to denaturation.

Question 19

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

Accepted Answer

Storage and transmission of genetic information.

Foundations of Biochemistry: Body Fluids, Biomolecules, Amino Acids, Proteins, and Enzymes

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