BIOL 636 Chapter 2

Which of the following is true of hydrogen bonds? A. The attraction between the oxygen atom of a water molecule and the hydrogen atom of another molecule constitutes a hydrogen bond. B. Hydrogen bonds form as covalent bonds between positively and negatively charged ions. C. Hydrogen bonds form between nonpolar portions of biomolecules. D. A and B are true. E. A, B, and C are true.

A

Equilibrium constant

A constant, characteristic for each chemical reaction, that relates the specific concentrations of all reactants and products at equilibrium at a given temperature and pressure

Acidosis

A metabolic condition in which the capacity of the body to buffer H+ is diminished; usually accompanied by decreased blood pH

Alkalosis

A metabolic condition in which the capacity of the body to buffer OH- is diminished; usually accompanied by an increase in blood pH

Titration curve

A plot of pH versus the equivalents of base added during titration of an acid

Conjugate acid-base pair

A proton donor and its corresponding deprotonated species

Condensation

A reaction type in which two compounds are joined with the elimination of water

Buffer

A system capable of resisting changes in pH, consisting of a conjugate acid-base pair in which the ratio of proton acceptor to proton donor is near unity

Hydrogen bond

A weak electrostatic attraction between one electronegative atom (such as oxygen or nitrogen) and a hydrogen atom covalently linked to a second electronegative atom

Hydrophobic effect

The aggregation of nonpolar molecules in aqueous solution, excluding water molecules; caused largely by an entropic effect related to the hydrogen-bonding structure of the surrounding water

Micelle

An aggregate of amphipathic molecules in water, with the nonpolar portions in the interior and the polar portions at the exterior surface, exposed to water

Henderson-Hasselbach equation

An equation relating pH, pKa, and ratio of the concentrations of proton-acceptor (A-) and proton-donor (HA) species in a solution

The pKa values for the three ionizable groups on tyrosine are pKa (-COOH) = 2.2, pKa (-NH3+) = 9.11, and pKa (-R) = 10.07. In which pH ranges will this amino acid have the greatest buffering capacity? A. At all pH's between 2.2 and 10.07 B. At pH's near 7.1 C. At pH's between 9 and 10 D. At pH's near 5.7 E. Amino acids cannot act as buffers.

C

Osmosis

Bulk flow of water through a semipermeable membrane into another aqueous compartment containing solute at a higher concentration

As climbers approach the summit of a mountain they usually increase their rate of breathing to compensate for the "thinner air" due to the lower oxygen pressures at higher elevations. This increased ventilation rate results in a reduction in the levels of CO2 dissolved in the blood. Which of the following accurately describes the effect of lowering the [CO2]dissolved on blood pH? A. It will result in an increase in the dissociation of H2CO3 -> H+ + HCO3- and a drop in pH. B. It will result in an increase in the dissociation of H2CO3 -> H2O + CO2 and a drop in pH. C. It will result in an increase in the association of H+ + HCO3- -> H2CO3 and an increase in pH. D. It will result in a decrease in the association of H+ + HCO3- -> H2CO3 and a decrease in pH. E. Lowering [CO2]dissolved has no effect on blood pH.

C

In a typical eukaryotic cell the pH is usually around 7.4. What is the [H+] in a typical eukaryotic cell? A. 0.00000074 M B. 6.6 uM C. 4 x 10^-8 D. 2.3 nM E. 7.4 x 10^-5 M

C

You are running your first marathon on a very warm day. You start to sweat heavily and realize that you may be in danger of dehydration. Why is severe dehydration potentially life-threatening? A. Water is a solvent for many biomolecules. B. Water is a chemical participant in many biological reactions. C. Water is necessary for buffering action in the body. D. Water's attraction to itself drives hydrophobic interactions. E. All of the above are true.

C

Hydrolysis

Cleavage of a bond, such as an anhydride or peptide bond, by addition of the elements of water, yielding two or more products

Amphipathic

Containing both polar and nonpolar domains

Consider a weak acid in a solution with a pH of 5.0. Which of the following statements is true? A. The weak acid is a proton acceptor. B. The weak acid has a lower affinity for its proton than does a strong acid. C. At its pKa, the weak acid will be totally dissociated. D. The [H+] is 10^-5 M. E. All of the above are true.

D

The pH of a sample of blood is 7.4; the pH of a sample of gastric juice is 1.4. The blood sample has an [H+]: A. 5.29 times lower than that of the gastric juice B. a million times higher than that of gastric juice C. 6,000 times lower than that of the gastric juice D. a million times lower than that of the gastric juice E. 0.189 times that of the gastric juice

D

Water derives all its special properties from its: A. cohesiveness and adhesiveness. B. high boiling point and melting point. C. small degree of ionization. D. polarity and hydrogen-bonding capacity. E. high dielectric constant.

D

Which of the following is true of pH? A. pH is the negative logarithm of [OH-]. B. Lemon juice, which has a pH of 2.0, is 60 times more acidic than ammonia, which has a pH of 12.0. C. Varying the pH of a solution will alter the pKa of an ionizable group in that solution. D. Varying the pH of a solution will alter the degree of ionization of an ionizable group in that solution. E. All of the above are true.

D

You mix 100 mL of solution of pH 1 with 100 mL of a solution of pH 3. The pH of the new 200 mL solution will be: A. 1.0 B. 2.0 C. 3.0 D. between 1.0 and 2.0 E. between 2.0 and 3.0

D

Carbonic acid has a Ka of 1.70 x 10^-4 and acetic acid has a Ka of 1.74 x 10^-5. Which of the following is true? A. Carbonic acid has the higher Ka of the two and would therefore be the best buffer at pH 6. B. The acid with the larger Ka is a better proton acceptor. C. Carbonic acid is the stronger acid and has a lesser tendency to lose its proton compared to acetic acid. D. Neither carbonic acid nor acetic acid can be effective buffers at any pH. E. Acetic acid is a weaker acid and has a lesser tendency to lose its proton compared to carbonic acid.

E

(T/F) H bonds can form only between water molecules.

False

(T/F) The oxygen atom in water has a partial positive charge.

False

Hydrophobic

Nonpolar; describes molecules or groups that are insoluble in water

Hydrophilic

Polar or charged; describes molecules or groups that associate with (dissolve easily in) water

Acid dissociation constant

The dissociation constant of an acid, describing its dissociation into its conjugate base and a proton

Bond energy

The energy required to break a bond

pKa

The negative logarithm of an equilibrium constant

pH

The negative logarithm of the hydrogen ion concentration

van der Waals interactions

Weak intermolecular forces between molecules as a result of each inducing polarization in the other

Ion product of water

The product of the concentrations H+ and OH- in pure water

(T/F) Each hydrogen atom of water bears a partial positive charge.

True

(T/F) H bonds are relatively weak compared to covalent bonds.

True