Q: Which equation represents the relationship between the change in entropy of the surroundings and the enthalpy change of a system?

$$\Delta S_{\text{surroundings}} = -\frac{\Delta H_{\text{system}}}{T}$$

Q: Which of the following is the correct form of the Henderson-Hasselbalch equation?

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

Q: At what pH is a weak acid (HA) exactly 50% dissociated?

When $$\text{pH} = \text{p}K_a$$

Q: Which of the following statements about buffers is correct?

A buffer is most effective at a pH near its $$\text{p}K_a$$ value.

Question 1

Which of the following best explains the biochemical unity underlying biological diversity, as illustrated by the comparison between an elephant and E. coli?

Accepted Answer

Both organisms share similar macromolecules and key metabolic processes, suggesting a common evolutionary ancestor.

Question 2

Which statement about the structure of DNA is correct?

Accepted Answer

DNA is a double helix composed of two antiparallel strands held together by hydrogen bonds between complementary bases.

Question 3

Which of the following correctly describes a hydrogen bond in the context of DNA base pairing?

Accepted Answer

A hydrogen bond occurs between an electronegative atom and a hydrogen atom covalently bonded to another electronegative atom, stabilizing the double helix.

Question 4

Which equation represents the relationship between the change in entropy of the surroundings and the enthalpy change of a system?

Accepted Answer

$$\Delta S_{	ext{surroundings}} = -\frac{\Delta H_{	ext{system}}}{T}$$

Question 5

A reaction has a negative $$\Delta G. $$Which of the following statements is true?

Accepted Answer

The reaction is spontaneous and will proceed without the input of energy.

Question 6

Which of the following best describes the hydrophobic effect in aqueous solutions?

Accepted Answer

Nonpolar molecules aggregate in water to increase the entropy of the surrounding water molecules.

Question 7

Which of the following is the correct form of the Henderson-Hasselbalch equation?

Accepted Answer

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

Question 8

At what pH is a weak acid (HA) exactly 50% dissociated?

Accepted Answer

When $$	ext{pH} = 	ext{p}K_a$$

Question 9

Which of the following best explains why the formation of the DNA double helix does not violate the second law of thermodynamics?

Accepted Answer

The decrease in entropy of the DNA is offset by an increase in entropy of the surroundings due to heat release.

Question 10

Which of the following statements about buffers is correct?

Accepted Answer

A buffer is most effective at a pH near its $$	ext{p}K_a$$ value.

Question 11

Which of the following is the correct expression for the equilibrium constant ($$K_w) of $$water at 25°C?

Accepted Answer

$$K_w = [H^+][OH^-] = 1.0 	imes 10$$^{-14}$$

Question 12

A solution contains 0.1 M acetic acid ($$	ext{p}K_a = 4.76) $$and 0.1 M sodium acetate. What is the pH of the solution?

Accepted Answer

4.76

Question 13

Which of the following interactions is the strongest in biological systems?

Accepted Answer

Covalent bonds

Question 14

Which of the following best describes the role of water's high dielectric constant in DNA structure?

Accepted Answer

It reduces electrostatic repulsion between negatively charged phosphate groups in the DNA backbone.

Question 15

Which of the following is a correct statement about van der Waals interactions in the DNA double helix?

Accepted Answer

They occur between stacked base pairs and help stabilize the helix.

Question 16

A DNA solution is exposed to a high pH. What is the most likely molecular consequence?

Accepted Answer

Loss of hydrogen bond donors in bases, leading to disruption of base pairing and denaturation of the helix.

Question 17

Which of the following best explains why phosphoric acid is an important buffer in biological systems?

Accepted Answer

Its $$	ext{p}K_a$$ values allow it to buffer effectively near physiological pH.

Question 18

Which of the following is true regarding the specificity of DNA sequence pairing?

Accepted Answer

Hydrogen bonds between complementary bases explain the specificity of sequence pairing.

Question 19

Which of the following best describes the relationship between $$\Delta G$$, $$\Delta H$$, and $$\Delta S in $$the context of biochemical reactions?

Accepted Answer

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

Chapter 1: Biochemistry – An Evolving Science

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