Question 1

Which of the following best explains why proteins are considered informational macromolecules, while polysaccharides are not?

Accepted Answer

Proteins have a unique sequence of monomers that determines their structure and function, whereas polysaccharides typically consist of repeating units and do not encode information.

Question 2

A mutation causes the substitution of valine for glutamate at position 6 in the β-chain of hemoglobin. Which property of valine most directly leads to the symptoms of sickle-cell anemia?

Accepted Answer

Valine is nonpolar and hydrophobic, causing hemoglobin molecules to aggregate via hydrophobic interactions.

Question 3

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

Accepted Answer

Disulfide bonds are covalent bonds formed between cysteine residues, stabilizing tertiary and quaternary structure.

Question 4

A scientist is studying the conversion of glucose-6-phosphate to fructose-6-phosphate in red blood cells. The equilibrium constant for this reaction at 25°C is $$Keq = 0.5. If $$the concentrations in the cell are $$[G6P] = 83 \, \mu M$$ and $$[F6P] = 14 \, \mu M$$, what is the sign of $$\Delta G'$$ for this reaction, and what does it indicate?

Accepted Answer

$$\Delta G' is $$negative, indicating the reaction is thermodynamically feasible and can proceed as written.

Question 5

Which of the following statements about enzyme catalysis is correct?

Accepted Answer

Enzymes lower the activation energy ($$E_A) $$required for the reaction, allowing more substrate molecules to reach the transition state.

Question 6

A researcher measures the initial velocity ($$v_0) of an $$enzyme-catalyzed reaction at various substrate concentrations and finds that $$v_0$$ approaches a maximum value ($$V_{max}) as $$substrate concentration increases. What kinetic model best describes this behavior, and what is the substrate concentration at which $$v_0$$ = \frac{V_{max}}{2}$$?

Accepted Answer

Michaelis–Menten kinetics; substrate concentration equals the Michaelis constant ($$K_m).$$

Question 7

Which of the following equations correctly relates the change in free energy ($$\Delta G) to $$enthalpy ($$\Delta H$$), entropy ($$\Delta S$$), and temperature ($$T$$)?

Accepted Answer

$$\Delta G = \Delta H - T\Delta S$$

Question 8

Which of the following best explains why increasing temperature is not a viable strategy for increasing reaction rates in living cells?

Accepted Answer

Most biological systems are isothermal, and high temperatures can denature enzymes, disrupting their structure and function.

Question 9

Which of the following is a major difference between competitive and noncompetitive enzyme inhibition?

Accepted Answer

Competitive inhibitors increase $$K_m$$ without affecting $$V_{max}$$, while noncompetitive inhibitors decrease $$V_{max}$$ without affecting $$K_m.$$

Question 10

A cell maintains reactions in a steady state far from equilibrium. Why is this essential for life?

Accepted Answer

At equilibrium, $$\Delta G' = 0$$ and no net work can be done, so maintaining a steady state allows continuous energy release and cellular work.

Question 11

Which of the following statements about the endosymbiont theory is supported by evidence from mitochondria and chloroplasts?

Accepted Answer

Mitochondria and chloroplasts contain circular DNA, bacterial-type ribosomes, and double membranes, supporting their origin from ancient bacteria.

Question 12

Which of the following best describes the effect of a positive $$\Delta G'$$ for a reaction under cellular conditions?

Accepted Answer

The reaction is not thermodynamically feasible as written, but can proceed if product concentration is kept low enough to make $$\Delta G'$$ negative.

Question 13

Which of the following is a correct statement about the Michaelis–Menten equation for enzyme kinetics?

Accepted Answer

At very low substrate concentration ($$[S] \ll K_m$$), the initial velocity $$v_0 is $$proportional to $$[S].$$

Question 14

Which of the following is a real-world example of feedback inhibition in a biosynthetic pathway?

Accepted Answer

The end product isoleucine inhibits threonine deaminase, the first enzyme in the pathway for isoleucine synthesis.

Question 15

Which of the following best describes the role of ribozymes in cells?

Accepted Answer

Ribozymes are RNA molecules with catalytic activity, such as peptidyl transferase in ribosomes.

Question 16

Which of the following is a consequence of the second law of thermodynamics for biological systems?

Accepted Answer

Spontaneous reactions in cells are always accompanied by an increase in the entropy of the universe and a decrease in the free energy of the system.

Question 17

A scientist is using isothermal titration calorimetry (ITC) to study ligand binding to a protein. Which thermodynamic parameters can be directly determined from ITC data?

Accepted Answer

The change in enthalpy ($$\Delta H$$), equilibrium constant ($$K_{eq}$$), and, from these, the change in free energy ($$\Delta G) $$and entropy ($$\Delta S).$$

Question 18

Which of the following statements about the structure and function of the plasma membrane is correct?

Accepted Answer

The plasma membrane is a lipid bilayer with hydrophobic tails facing inward and hydrophilic heads facing outward, forming a permeability barrier.

Cell Biology Study Guide: Macromolecules, Cell Structure, Bioenergetics, and Enzyme Function

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