FORM A

BCH 3053 Introductory Biochemistry Summer, 2015

Exam 1, May 29, 2015

Choose the best answer from the multiple choices.

Question #21 and 22 are Extra Credit

pH+pOH =14

𝑝𝐻 = 𝑝𝐾𝑎 + log[𝑐𝑜𝑛𝑗𝑢𝑔𝑎𝑡𝑒 𝑏𝑎𝑠𝑒]

[𝐶𝑜𝑛𝑗𝑢𝑔𝑎𝑡𝑒 𝑎𝑐𝑖𝑑]

𝑝𝐻 = − log[𝐻+]

∆𝐺 = 𝐻 − 𝑇∆𝑆

FORM A

FORM A

1. The equation below describes the free energy change for a reaction. Which of the following statements is

always true?

∆𝐺 = 𝐻 − 𝑇∆𝑆

a) When a reaction results in an increase in entropy G is always positive.

b) When a reaction results in an increase in entropy G is always negative.

c) When H is negative the reaction is always spontaneous.

d) When G =0 the rates of the forward and reverse reactions are always equal.

e) When G is positive the reaction is spontaneous.

2. The compound below is an example of what class of compounds?

a) ketone

a) ether

c) aldehyde

d) carboxylic acid

e) ester

3. Consider the ionization of phosphoric acid:

H3PO4 H+ + H2PO4- pK1=2.15

H2PO4- H+ + HPO4

2- pK2=7.20

HPO4-2 H+ + PO4

3- pK3=12.40

What is the predominant ion form at pH=8.20?

a) H3PO4

b) H2PO4-

c) HPO42-

d) PO43-

e) PO42-

FORM A

4.The pKa of compound is 3.57. The pH of a solution of the compound is 7.4.The concentration of the conjugate

base is 14mM.What is the concentration of the conjugate acid?

a) 2.1 micromolar

b) 4.9 micromolar

c) 1.1 micromolar

d) 6.1micromolar

e) 5.5 micromolar

5. Hydrophobic interactions are

a) enthalpy driven

b) driven by the tendency for water to form ordered structures to lower the free energy of the system

c) driven by the tendency of water to interact with nonpolar molecules

d) entropy driven

e) driven by the attraction of nonpolar molecules with other nonpolar molecules

6. The pH of 7 x 10-5 M NaOH is:

a) 4.15

b) 7.34

c) 9.85

d) 10.98

e) 12.5

7. Micelles are held together by:

a) covalent bonds

b) hydrogen bonds

c) ion-dipole forces

d) induced dipoles

e) ionic interactions

FORM A

8. Each of the molecules (Compounds 1, 2, 3, and 4) below is dissolved in a buffered solution of pH 8.The

acidic hydrogens are labeled with a star. The correct charges on the molecules are:

Compound

1. Compound

2. Compound

3. Compound

4.

a) 0 +1 +1 0

b) -1 +0 +1 0

c) 0 +1 +1 -1

d) -1 0 0 -1

e) +1 0 0 0

9. What is the ratio of conjugate base to conjugate acid when threonine is in solution at pH 9.85?

a) 1.04

b) 0.589

c) 0.786

d) 0.403

e) 1.70

1. pKa = 4.0 2. pK

a=7.0 3. pK

a=9. 5 4. pK

a=9.6

FORM A

10. Refer to the table and the titration curve below. Which compound is illustrated by the titration curve?

Compound pK1 pK

2 pK

3

Phosphoric acid

2.15 7.20 12.15

Acetic acid 4.76

Succinic acid

4.21 5.46

Boric acid 9.24 12.74

Glycine 2.4 9.8

a) phosphoric acid

b) acetic acid

c) succinic acid

d) boric acid

e) glycine

FORM A

11. What is the isoelectric point of the structure below. The structure is drawn at pH 7.

pK3 =10.9 pK1=2.09 pK2=9.6

a) 5.46

b) 10.25

c) 8.90

d) 11.38

e) 7.33

12.What is the charge on the following peptide at pH 12?

Gly-Ala-Trp-Ala-Glu-Gln-Ser

a) -1

b) -2

c) 0

d) +1

d) +2

e) -3

FORM A

13. The three-dimensional structure and folding of a protein is determined by;

a) the primary structure, or sequence of the amino acids

b) the covalent bonds formed between the secondary structures

c) the covalent bonds formed between the tertiary structures

d) the arrangement of the monomer units with respect to each other

e) the interactions with other protein chains

14. Ramachandran plots reveal:

a) the sequences of the amino acids in proteins that are sterically allowed

b) the noncovalent interactions among tertiary structures in proteins

c) the conformations that are sterically allowed in secondary structures

d) the quaternary structures in proteins that that yield stable conformations

e) the covalent bonds that form between tertiary structures in proteins

15. In the alpha helix:

a) the hydrogen bonds are within one molecule and parallel to the axis of the helix

b) the hydrogen bonds are between adjacent strands and parallel to the axis of the helix

c) hydrogen bonds are between adjacent strands that are arranged in an antiparallel manner

d) the hydrogen bonds are between adjacent strands that are arranged in a parallel manner

e) the sidechains radiate into the center of the helix

16. Which of the following statement is true?

a) The quaternary structure of myoglobin is largely responsible for oxygen binding

b) Plots of % saturation versus partial pressure of oxygen in hemoglobin are hyperbolic.

c) H+, CO2, Cl-, and 2,3-bisphosphoglycerate (BPG) affect the ability of hemoglobin to bind and

transport oxygen.

d) H+, CO2, Cl-, and 2,3-bisphosphoglycerate (BPG) affect the ability of myoglobin to bind and transport

oxygen.

e) The oxygen binding exhibited by hemoglobin exhibits a negative cooperativity.

FORM A

17. Which of the following statements is false?

a) Collagen is rich in glycine and proline

b) Collagen forms left handed single helices

c) Collagen forms right handed superhelices when three left handed single helices intertwine

d) Collagen is a fibrous protein

e) Collagen winds into a quaternary structure with 4 monomer units.

18. Which of the following explains the binding behavior of oxygen to the protein in question?

a) The sigmoidal binding curve from oxygen in myoglobin explains why it is easily saturated at low oxygen

pressures.

b) Myoglobin exhibits cooperativity in oxygen binding as a result of conformational changes that occur when

the first oxygen is bound to the hemoglobin.

c) Both hemoglobin and myoglobin exhibit allosteric control in oxygen binding.

d) Oxygen exhibits cooperative binding in hemoglobin as a result of conformational changes in its

quaternary structure.

e) Hyperbolic binding curves in hemoglobin indicate allosteric control.

19. Antiparallel β-sheets have:

a) sheets that progress from N to C termini in the same direction.

b) usually all of their hydrophobic residues on one side of the sheet.

c) long sequences of proline residues.

d) all hydrophilic residues.

e) fibers that can be highly stretched and elongated.

20. Polylysine is a random structure when the pH is less than 11, while it forms an alpha-helix if the pH is

raised to greater than 12. This is because at pH 12:

a) the lysine residues are negatively charged which electrostatically stabilizes the helix.

b) the positive charges on the lysine residues stabilize the alpha-helix.

c) the lysine residues are neutral which eliminates electrostatic repulsion between the R groups.

d) the high concentration of OH- ions in solution reduces the electrostatic repulsion between the R-groups.

e) the lysine side chain changes configuration with pH.

FORM A

21. Histidine has a low pKa compared to Lysine and Arginine. Why?

a. It is more basic that arginine and lysine.

b. It is more stable when the side chain is protonated.

c. The neutral form of the side chain tautomerizes.

d. The charged form of the side chain tautomerizes.

e. The side chain remains protonated at pHs that approach 10.0.

22. What does region III in the plot below denote?

a) The region where neither the amino group nor the carboxylic acid group are charged.

b) The region where both the amino group and the carboxylic acid group have lost their acidic hydrogens

c) The region of maximum buffering capacity

d) The region where the conjugate base concentration = the conjugate acid concentration.

e) The region where the amino acid does not migrate in an electric field.