Mastering Bio Multiple Choice

Measurements show that the pH of a particular lake is 4.0. What is the hydrogen ion concentration of the lake?

4.0 M
4%
10^-4 M
10^-10 M
10^4 M

10^-4 M

What is the molar concentration of [H3O+] in a cola that has a pH of 3.120?

7.58 × 10^−4
7.59 × 10^−4
7.6 × 10^−4
3.120 × 10^−3
0.494
1.318 × 10^3

7.59 × 10^−4

Your tank of swamp fish needs a pH of 5, and the pH is 7 at present. What should you do to the H+ concentration?

-Reduce it to 1/100 of its present value.
-Cut it in half.
-Raise it to 200 times its present value.
-Raise it to 100 times its present value.
-Double it.

-Raise it to 100 times its present value.

Which statement is true of pH buffers?

(a) They consist of strong acids and strong bases.
(b) They keep the pH of the blood constant.
(c) They consist of weak acids and weak bases.
Both (a) and (b).
Both (b) and (c).

(c) They consist of weak acids and weak bases.

A buffer consists of undissociated acid (HA) and the ion made by dissociating the acid (A-). How does this system buffer a solution against decreases in pH?

(a) HA dissociates and releases H+ and A- into solution.
(b) A- reacts with H+ to become HA.
(c) As the solution loses H+, HA replaces the lost H+.
Both (a) and (c).
None of the above.

(b) A- reacts with H+ to become HA.

Buffers work best when …

-about half of the buffer molecules are dissociated.
-5% nearly all of the buffer molecules are dissociated.
-the ratio of H+ to OH- is close to 1.0.
-the pH is nearly neutral.
-nearly all of the buffer molecules are undissociated.

-about half of the buffer molecules are dissociated.

How does the way a buffer stabilizes pH during addition of acid differ from the way the same buffer stabilizes pH during addition of base?

a. The same buffer can’t work for both acid and base.
b. In one case the buffer is strong; in the other case it’s weak.
c. It’s the same reaction running backward or forward.
d. In one case it adds H+; in the other case it adds OH-.

c. It’s the same reaction running backward or forward.

Which answer helps to explain why all living cells need pH buffers?

a. Nucleic acids must have positive charges to form double helices.
b. Amino acid side chains have many carboxyl and amino groups.
c. Hydrogen bonds only form at medium pH values.
d. ATP will not deliver energy if it is ionized.

b. Amino acid side chains have many carboxyl and amino groups.

To make a buffer, you need to …

(a) combine equal amounts of a strong acid and a strong base in water.
(b) put either a strong acid or a strong base in water.
(c) adjust the pH to 7.0.
(d) have a weak acid or a weak base half ionized in water.
Both (a) and (c).

(d) have a weak acid or a weak base half ionized in water.

If the pH of a solution is decreased from 9 to 8, it means that the concentration of _____.

a. H+ has increased tenfold (10X) compared to what it was at pH 9
b. H+ has doubled compared to what it was at pH 9
c. H+ has decreased to one-tenth (1/10) what it was at pH 9
d. OH- has increased tenfold (10X) compared to what it was at pH 9

a. H+ has increased tenfold (10X) compared to what it was at pH 9

Select the statement that best describes a buffer.

a. A buffer prevents the pH of a solution from changing when an acid or base is added.
b. A buffer stabilizes the pH of a solution by preventing acids or bases from dissociating.
c. A buffer causes acidic solutions to become alkaline, and alkaline solutions to become acidic.
d. A buffer resists change in pH by accepting hydrogen ions when acids are added to the solution and donating hydrogen ions when bases are added.
e. Buffered solutions are always neutral, with a pH of 7.

d. A buffer resists change in pH by accepting hydrogen ions when acids are added to the solution and donating hydrogen ions when bases are added.

Which of the following 3 functional groups is most likely to gain a proton and become positively charged?

a. The amino group is most likely to gain a proton.
b. The carboxyl group is most likely to gain a proton.
c. The hydroxyl group is most likely to gain a proton.

a. The amino group is most likely to gain a proton.

Which statement about a methyl functional group is correct?

a. A methyl group consists of a carbon bonded to three hydrogen atoms.
b. A methyl group is polar.
c. A methyl group may be negatively charged.

a. A methyl group consists of a carbon bonded to three hydrogen atoms.

Identify the functional groups.

a. Lipids and proteins are functional groups.
b. Amino and carboxyl are functional groups.
c. DNA and RNA are functional groups.

b. Amino and carboxyl are functional groups.

Which action could produce a carbonyl group?

a. the addition of a hydroxyl to a phosphate
b. the addition of a sulfhydryl to a carboxyl
c. the replacement of the -OH of a carboxyl group with hydrogen
d. the addition of a thiol to a hydroxyl
e. the replacement of the nitrogen of an amine with oxygen

c. the replacement of the -OH of a carboxyl group with hydrogen

Which functional group is most likely to ionize when a base is added to the solution?
a. Carbonyl group
b. Amino group
c. Carboxyl group
d. Phosphate group
e. Hydroxyl group

c. Carboxyl group. Carboxyl groups easily donate an H+ to water or to bases

Normal hemoglobin is a tetramer, consisting of two molecules of β hemoglobin and two molecules of α hemoglobin. In sickle-cell disease, as a result of a single amino acid change, the mutant hemoglobin tetramers associate with each other and assemble into large fibers. Based on this information alone, we can conclude that sickle-cell hemoglobin exhibits _____.

a. only altered primary structure
b. only altered tertiary structure
c. only altered quaternary structure
d. altered primary structure and altered quaternary structure; the secondary and tertiary structures may or may not be altered

d. altered primary structure and altered quaternary structure; the secondary and tertiary structures may or may not be altered

The helical foldings of proteins are stabilized mainly by bonds between …

a. side chains.
b. water molecules.
c. ionic groups.
d. CO and NH.
e. S and S.

d. CO and NH

The helical foldings in proteins …

a. are part of the protein’s primary structure.
b. are kept folded by forces between side chains on adjacent turns of the helix.
c. are kept folded by hydrogen bonds.
d. are kept folded by base-pairing.
e. None of the above.

c. are kept folded by hydrogen bonds.

Which fact results from the presence of both polar and nonpolar side chains in a protein?

a. Each protein has many functions.
b. Proteins ionize when they are placed in water.
c. Water has a strong effect on tertiary structure.
d. pH has a strong effect on secondary structure.
e. A protein’s folding doesn’t depend on the polarity of the environment.

c. Water has a strong effect on tertiary structure

The sequence of polar and nonpolar side chains has a strong effect on a protein’s folding mainly because …

a. polar side chains attract one another.
b. water repels nonpolar side chains.
c. nonpolar side chains repel water.
d. nonpolar side chains attract one another.
e. water attracts polar but not nonpolar groups.

e. water attracts polar but not nonpolar groups

When a protein has been unfolded enough to lose its function, the protein has been …

a. metastasized.
b. distempered.
c. denatured.
d. hydrolyzed.
e. None of the above.

c. denatured

Which factor is most important in determining a protein’s optimum pH?

a. The number of amino groups in the protein’s backbone.
b. The number of backbone carboxyl groups.
c. The sensitivity of hydrocarbon side chains to pH.
d. The locations of side-chain carboxyl groups.
e. The pH of the protein’s environment.

d. The locations of side-chain carboxyl groups The effect of pH depends on the number and locations of ionizable side chains, including those with carboxyl groups. pH affects their ionization, which determines the balance of attractions and repulsions between side chains.

Why don’t cells rely more on disulfide bridges to stabilize the folding of proteins?

a. They make the protein rigid. Many proteins change their shape as they work.
b. Though strong, disulfide bridges put a strain on the backbone.
c. Disulfide bridges are too weak. Proteins can get more stability from ionic forces.
d. Disulfide bridges can only occur just after proline in the amino acid sequence.
e. There’s no room for more disulfide bridges. Most proteins have many of them.

a. They make the protein rigid. Many proteins change their shape as they work.

To make a disulfide bridge, it’s necessary to …

a. perform a hydrolysis reaction.
b. remove an H and an OH.
c. remove two H atoms.
d. remove two OH groups.
e. None of the above.

c. remove two H atoms The two cysteines start with -SH groups. They end up linked as -S-S-

Some of the strongest biological structures (e.g., beaks and claws) are made of many molecules of the protein keratin. What else is true of structures made of keratin?

(a) Disulfide bridges bind the proteins together.
(b) Each protein is a single long alpha helix.
(c) Hair is another example.
d. Both (a) and (b).
e. (a), (b), and (c).

e. (a), (b), and (c)

Which level(s) of protein structure may be stabilized by covalent bonds?

a. Primary, tertiary and quaternary levels of protein structure
b. None of the levels of protein structure is stabilized by covalent bonds.
c. Secondary level of protein structure

a. Primary, tertiary and quaternary levels of protein structure

What type of bond joins together amino acids?

covalent peptide bonds

What stabilizes tertiary structure of proteins?

Tertiary structure, producing the unique structure of a protein, is stabilized by interactions among the R groups on each amino acid in the protein. Tertiary structure may be stabilized by covalent bonds, called disulfide bridges, that form between the sulfhydryl groups (SH) of two cysteine monomers. Tertiary structure may also be stabilized by weaker interactions, including hydrogen bonds between polar and/or charged areas, ionic bonds between charged R groups, and hydrophobic interactions and van der Waals interactions among hydrophobic R groups