Question 1

Which of the following statements best explains why living systems require a constant input of energy?

Accepted Answer

Because living systems are highly ordered and must oppose entropy, which requires work and energy input.

Question 2

Which equation describes the relationship between pH, pKa, and the ratio of conjugate base to weak acid in a buffer system?

Accepted Answer

$$\mathrm{pH} = \mathrm{p}K_a + \log\left(\frac{[A^-]}{[HA]}\right)$$

Question 3

A patient is experiencing metabolic acidosis. Which of the following best describes how the blood buffering system responds?

Accepted Answer

The concentration of $$[$$HCO_3$$^-]$$ decreases as it neutralizes excess $$H^+$$, and respiration rate increases to expel more $$CO_2.$$

Question 4

Which of the following is TRUE regarding the role of enzymes in biochemical reactions?

Accepted Answer

Enzymes lower the activation energy but do not change the overall free energy ($$\Delta G) of $$the reaction.

Question 5

Given the reaction: $$\mathrm{Glucose} + \mathrm{ATP} ightarrow \mathrm{Glucose	ext{-}6	ext{-}phosphate} + \mathrm{ADP}$$, which enzyme catalyzes this reaction?

Accepted Answer

Hexokinase

Question 6

Why is the carbonic acid-bicarbonate buffer system effective in blood, even though its pKa (6.1) is not equal to the physiological pH (7.4)?

Accepted Answer

Because the system is open and $$CO_2$$ can be regulated by respiration, allowing dynamic adjustment of $$[$$HCO_3$$^-]$$ and $$[CO_2$].$$

Question 7

Which of the following best describes the relationship between $$\Delta G_1$, $$\Delta $$G_2$$, and $$\Delta G_3$ in a coupled reaction system?

Accepted Answer

$$\Delta G_3 = \Delta G_1 + \Delta G_2$$

Question 8

A buffer is prepared with equal concentrations of acetic acid ($$CH_3COOH) $$and acetate ($$CH_3COO^-). $$What is the pH of the solution if the $$pK_a of $$acetic acid is 4.76?

Accepted Answer

4.76

Question 9

Which property of water is most critical for the aqueous environment of biochemical reactions?

Accepted Answer

Its ability to form hydrogen bonds, making it an excellent solvent for polar and charged molecules.

Question 10

Which of the following best explains why enzyme malfunction can lead to disease?

Accepted Answer

Enzymes catalyze essential biochemical reactions, so their malfunction disrupts metabolic pathways and homeostasis.

Question 11

If a buffer has a total concentration of 0.1 M and is composed of 0.06 M $$HA$$ and 0.04 M $$A^-$$, what is the mole fraction of $$A^-$$?

Accepted Answer

0.4

Question 12

Which of the following is a correct statement about the titration curve of a weak acid?

Accepted Answer

The buffering region is centered around the $$pK_a$$ and extends approximately $$\pm 1 pH $$unit.

Question 13

Which of the following best describes the effect of pH on enzyme activity?

Accepted Answer

Each enzyme has an optimal pH at which its activity is maximal; deviations from this pH reduce activity.

Question 14

Which of the following is NOT a property of biological buffers?

Accepted Answer

They are strong acids that completely dissociate in water.

Question 15

A solution contains $$[$$HCO_3$$^-] = 24 mM $$and $$[CO_2$] = 1.2 mM. $$Using the modified Henderson-Hasselbalch equation for blood, what is the pH?

Accepted Answer

$$\mathrm{pH} = 6.1 + \log\left(\frac{24}{1.2}\right) = 6.1 + \log(20) \approx 7.4$$

Question 16

Which of the following best explains why the pH of lysosomes is much lower than that of the cytoplasm?

Accepted Answer

Lysosomal enzymes require an acidic environment for optimal activity.

Question 17

Which of the following is a consequence of adding a strong base to a buffer system composed of $$HA$$ and $$A^-$$?

Accepted Answer

The $$HA$$ will donate protons to neutralize the base, converting to $$A^-$$ and minimizing the pH change.

Question 18

Which of the following is a reason why understanding biochemistry is foundational for medicine?

Accepted Answer

Most drugs target proteins, and many diseases result from aberrant proteins.

Lecture 1: Introduction to Protein Structure & Metabolism

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