UBCH 240 Chapter 2

What is the pH of an aqueous solution with the hydronium ion concentration [H3O+] = 2 x 10-14 M ?

13.7

Which of the following statements about macroions, large polyelectrolyte molecules, is NOT true? A) Maximum solubility is achieved when the solution containing such a molecule is near the pI for that molecule. B) Concentrations of salts that mimic the ionic strength of cells tend to keep macromolecules in solution. C) These large molecules can often interact tightly with other molecules of opposite net charge. D) At high pH, macromolecules often carry net negative charges and therefore repel each other.

A) Maximum solubility is achieved when the solution containing such a molecule is near the pI for that molecule.

Hydrogen bonds share features of both covalent and noncovalent bonds. A) True B) False

A) True

Water is both a hydrogen bond donor and acceptor. A) True B) False

A) True

Atoms with the same number of protons but with different electrical charges _____. A) are different ions B) have different numbers of neutrons C) have different atomic numbers D) have different atomic masses E) are different isotopes

A) are different ions

Each water molecule is joined to _____ other water molecules by ____ bonds. A) four ... hydrogen B) three ... ionic C) four ... polar covalent D) two ... hydrogen E) two ... polar covalent

A) four ... hydrogen

What name is given to the bond between water molecules? A) hydrogen B) hydrophobic C) single (nonpolar) covalent D) polar covalent E) ionic

A) hydrogen

Which statements regarding the Henderson-Hasselbalch equation are true? 1) If the pH of the solution is known as is the pKa for the acid, the ratio of conjugate base to acid can be determined. 2) At pH = pK a for an acid, there is an equal amount of conjugate base to acid in solution. 3) At pH >> pK a for an acid, the acid will be mostly ionized. 4) At pH << pK a for an acid, the acid will be mostly ionized. A) 2, 3, and 4 are true. B) 1, 2, and 3 are true. C) 1, 2, and 4 are true. D) All of the listed statements are true.

B) 1, 2, and 3 are true.

Which statements about hydrogen bonds are correct? 1) Hydrogen bonds are the interaction between a hydrogen atom bonded to an electronegative element and the lone pair of electrons on a nearby electronegative atom. 2) The atom to which the hydrogen atom is covalently bonded is the hydrogen-bond donor. 3) The distance between the covalently bound H atom and its hydrogen-bonding donor is the sum of its van der Waals radii. 4) Hydrogen bonds can be stronger interactions than even charge-charge interactions. A) 1, 2, and 3 are correct. B) 1, 2, and 4 are correct. C) 2, 3, and 4 are correct. D) All of the listed statements are correct.

B) 1, 2, and 4 are correct.

Which statements about hydrogen bonds are correct? 1) Hydrogen bonds are the interaction between a hydrogen atom bonded to an electronegative element and the lone pair of electrons on a nearby electronegative atom. 2) The atom to which the hydrogen atom is covalently bonded is the hydrogen-bond donor. 3) The distance between the covalently bound H atom and its hydrogen-bonding donor is the sum of its van der Waals radii. 4) Hydrogen bonds can be stronger interactions than even charge-charge interactions. A) 2, 3, and 4 are correct. B) 1, 2, and 4 are correct. C) 1, 2, and 3 are correct. D) All of the listed statements are correct.

B) 1, 2, and 4 are correct.

Carbonated cola is more acidic than coffee or even orange juice because cola contains phosphoric acid. What is the molar concentration of [H3O+] in a cola that has a pH of 3.120? (For help with significant figures, see Hint 3.) A) 7.58 × 10−4 B) 7.59 × 10−4 C) 7.6 × 10−4 D) 3.120 × 10−3 E) 0.494 F) 1.318 × 103

B) 7.59 × 10−4

What pH gradient would you choose for this experiment? A) A pH gradient between 8.0 to 12.0. B) A pH gradient between 2.0 to 7.0. C) A pH gradient between 2.0 to 5.0. D) A pH gradient between 7.0 to 10.0.

B) A pH gradient between 2.0 to 7.0.

For molecules with multiple ionizable groups, such as glycine, which of the following statements is true? A) When the pH is near the pI, the solution is near its maximum buffering ability. B) At pH near the pI, nearly all the molecules carry no net charge. C) At a pH near the pI, nearly all the molecules carry a net negative charge. D) At a pH near the pI, nearly all the molecules carry a net positive charge.

B) At pH near the pI, nearly all the molecules carry no net charge.

Amphipathic molecules are not able to interact via van der Waals forces. A) True B) False

B) False

Glycine cannot serve as a buffer because it has two ionizable groups. A) True B) False

B) False

The average charge on an amino acid below its pI will be positive. A) True B) False

B) False

The pKa of each amino acid residue in a protein will not be influenced by the adjacent residue. A) True B) False

B) False

Which of the following statements about acids and bases is INCORRECT? A) Bases need not contain -OH directly; instead, they can increase the concentration of -OH by deprotonating water. B) Water acts as a weak acid. C) A Brønsted base is a proton acceptor. D) A strong acid has a weak conjugate base.

B) Water acts as a weak acid.

Which would be better for separation: gel electrophoresis or isoelectric focusing? A) gel electrophoresis B) isoelectric focusing

B) isoelectric focusing

In gel electrophoresis DNA molecules migrate from _____ to _____ ends of the gel. A) acidic ... basic B) negative ... positive C) basic ... acidic D) long ... short E) positive ... negative

B) negative ... positive

Many proteins interact with DNA at physiological pH because: A) both proteins and DNA are at their isoelectric points at physiological pH and tend to aggregate. B) the negatively charged DNA is electrostatically attracted to positively charged regions on proteins. C) proteins are naturally attracted to DNA regardless of the pH. D) proteins and DNA interact using mainly hydrophobic interactions. D) the positively charged DNA is electrostatically attracted to negatively charged regions on proteins.

B) the negatively charged DNA is electrostatically attracted to positively charged regions on proteins.

Which of the following in biological compounds are sufficiently electronegative to serve as strong donors in a hydrogen bond? A) Nitrogen and hydrogen B) Hydrogen and oxygen C) Oxygen and nitrogen D) Nitrogen and carbon E) Hydrogen and carbon

C) Oxygen and nitrogen

Which of the following properties of water make(s) life possible? A) Water has strong hydrogen bonding interactions between molecules, which allow it to exist at ambient temperature as a liquid. B) Water's high dielectric constant allows it to dissolve polar and charged molecules alike. C) Water is less dense as a solid than as a liquid. D) All of the listed properties of water make life possible.

D) All of the listed properties of water make life possible.

Which statements about lipid bilayers are true? 1) Their formation is driven by the hydrophobic effect. 2) The amphipathic molecules that make up the bilayers orient themselves such that their polar head groups point out toward the aqueous solvent and their hydrophobic tails are pointed toward the interior of the bilayer. 3) They serve the role of physical compartmentalization of components within a cell. 4) They are made primarily from phospholipids. A) 1, 2, and 3 are true. B) 1, 2, and 4 are true. C) 1, 3, and 4 are correct. D) All of the listed statements are true.

D) All of the listed statements are true.

Noncovalent bonds are critically important to the function of biomolecules. Which of the following is/are (a) valid reason(s) for this importance? A) Noncovalent interactions are made up of hydrogen bonding, electrostatic interactions, and dispersion forces. B) Their bond energies are ~10-100 times weaker than ordinary covalent bonds. C) The effect of these weak interactions is cumulative. D) All of the listed statements are valid reasons for this importance.

D) All of the listed statements are valid reasons for this importance.

Which of the following statements about noncovalent bonding interactions is NOT true? A) Van der Waals interactions, also known as dispersion forces, are the weakest of the attractive noncovalent bonding interactions. B) All noncovalent bond interactions are inherently electrostatic in nature. C) A charge may induce formation of a dipole in a nearby polarizable molecule. D) Charge-induced dipole interactions are inversely proportional to the square of the distance between the two atoms.

D) Charge-induced dipole interactions are inversely proportional to the square of the distance between the two atoms. SubmitMy AnswersGive Up

Each of the following is a noncovalent interaction EXCEPT: A) a van der Waals interaction. B) the interaction between an amino and a carboxylate group. C) a hydrogen bond. D) a carbon-hydrogen bond. E) an interaction between NH3+ and a water molecule.

D) a carbon-hydrogen bond.

An ionic bond involves _____. A) water avoidance B) the unequal sharing of an electron pair C) no atoms other than sodium and chlorine D) an attraction between ions of opposite charge E) the sharing of a single pair of electrons

D) an attraction between ions of opposite charge

The tendency of an atom to pull electrons toward itself is referred to as its _____. A) tonicity B) ionic potential C) polarity D) electronegativity E) covalency

D) electronegativity

The unequal sharing of electrons within a water molecule makes the water molecule _____. A) hydrophobic B) change easily from a liquid to gaseous form C) have a low surface tension D) polar E) ionic

D) polar

Which of the following is TRUE of hydrophobic molecules? A) Dissolving in water decreases the entropy of the mixture. B) Water forms a cage-like structure around them. C) They have limited solubility in water. D) They self-associate by releasing some of the surrounding water molecules. E) All of the above

E) All of the above

In salt, what is the nature of the bond between sodium and chlorine? A) polar covalent B) nonpolar covalent C) hydrogen D) hydrophobic E) ionic

E) ionic

The most important noncovalent interaction in biochemistry is the ________ bond.

hydrogen

The single-charge difference would result in a _______ difference in mobility in a normal ____________ experiment (which separates chains based on size), but would make a detectable difference in pI.

small, gel electrophoresis