Biochemistry   

Introduction to Biochemistry       Old Exam Questions     Dr. Gustin             Exam 1

 

1. Which of the following only hydrogen bonding as its strongest intermolecular force?

 

1. CH₄
2. CH₃NH₂
3. HI
4. HCl
5. All except d

 

2. Which of the following is hydrophobic?

 

1. CH₃OH
2. CH₂NH₂
3. C₈H₁₈
4. NaCl
5. All except d

 

3. Which of the following is true at equilibrium for a weak acid such as HC₂H₃O₂(aq) at 25^oC?

 

HC₂H₃O₂(aq)  +  H₂O(l) <-> H₃O⁺(aq)  +  C₂H₃O₂^–(aq)

 

1. There are equal amounts of acid and ions at equilbrium.
2. There is more HC₂H₃O₂(aq) than H₃O⁺(aq) and C₂H₃O₂^–(aq) at equilibrium.
3. There is more H₃O⁺ and C₂H₃O₂^– than HC₂H₃O₂ at equilibrium.
4. K_a for the acid is very large.

 

4. Which is the best buffer solution for resisting pH changes at 4.00?

 

Buffer solution 1:  H₃PO₄/H₂PO4^–   pKa = 2.14

Buffer solution 2:   H₂CO₃/HCO₃^–  pKa = 6.35

Buffer solution 3:   NH₃/NH₄⁺             pKa=9.25

Buffer solution 4:   HF/F^–                pK_a = 3.17

 

1. Solution 1
2. Solution 2
3. Solution 3
4. Solution 4

For questions 5-7, please refer to the following titration curve of a weak acid (H₂A) and strong base.

 

5. What is approximately the pH at the first equivalence?

 

1. 2.3
2. 5.0
3. 7.5
4. 10.0
5. 13.0

 

6. Which species exists at pH=10.0?

 

1. H₂A
2. HA^–
3. A^2-
4. 50% HA^– and A^2-

 

7. What is approximately pKa₂ of the acid?

 

1. 2.3
2. 5.0
3. 7.5
4. 10.0
5. 13.0

 

8. Which of the following is the conjugate base of H₂PO₄^–?

 

1. H₂PO₄^–
2. HPO₄^2-
3. PO₄^3-
4. H₃PO₄
5. None of the above

 

9. Which acid is the strongest of the following choices?

 

H₃PO₄              pKa = 2.14

H₂CO₃              pKa = 6.35

NH₃                      pKa=9.25

HF                    pK_a = 3.17

 

1. H₃PO₄      b. H₂ CO₃    c. NH₃   d. HF

 

For questions 10-11, refer to the conversion of glucose 1-phosphate to glucose 6-phosphate is an equilibrium.

 

Glucose 1-phosphate  <-> glucose 6-phosphate

 

1. Removal of glucose 6-phosphate will cause

 

 

1. 1. the reaction to shift right
   2. the reaction to shift left
   3. the reaction to stop
   4. the reaction form more reactant

 

1. The ΔG for the reaction is -7.5 kJ/mol. What is true about the reaction?

 

1. 1. The reaction is not spontaneous.
   2. The reaction requires free energy.
   3. The reaction is spontaneous.
   4. The reaction favors the formation of glucose 1-phosphate.

 

1. Which of the following are buffered solution that will have pH=pKa?

 

1. 3.0 M HCl
2. 3.0 M HC₂H₃O₂  +  3.0 M C₂H₃O₂^–
3. 1.0 M HC₂H₃O₂  +  3.0 M C₂H₃O₂^–
4. 2. 0 M HC₂H₃O₂  +  3.0 M C₂H₃O₂^–
5. All of the above

 

For questions 13-14, refer to the following equation:

 

ΔG = ΔH- TΔS

 

13.If a reaction releases free energy, the reaction is ____________.

 

1. 1. Endothermic
   2. Endergonic
   3. Exothermic
   4. Exergonic

 

14.If the ΔH=0 and if the entropy of the system increases, ΔG will be

 

1. Negative and free energy will be released.
2. Positive and free energy will be released.
3. Positive and free energy will be required.
4. Negative and free energy will be required.

 

15.The pI of valine is

 

a.2.3      b. 9.7   c. 1.0    d. 6.0     e. None of the above

 

 

16.The following is the structure for glucose.

a.

Which of the following is true about glucose?

 

1. The strongest intermolecular force in the molecule is van der waals forces.
2. Glucose can hydrogen bond with water and it is water soluble.
3. Glucose is a carboxylic acid.
4. Glucose is non-polar.

 

17. Which of the following is true about amino acids?

 

1. All amino acids are essential.
2. At pH=7.00, all amino acids are in Zwitterion form.
3. Amino acids in proteins are found in the D configuration.
4. There are 22 amino acids.
5. All amino acids except glycine are chiral.

 

18. Which of the following amino acids has a hydrophobic side chain?

 

1. K   b W    c. S    d. T    e. none of the above

 

19. Which of the following would be attracted to water on the outside of a protein?

 

1. Ser    b.  Ala   c.  Leu     d.   Phe     e. Ile

.

20. Which of the following amino acids has an acidic R group?

 

1. Lys     b. Arg     c. His    d. Asp   e. Trp

 

21. Which amino acid can form disulfide linkages?

 

1. Thr     b. Lys    c. His     d. Cys      e. Ser

 

22. Which of the following amino acids is in its Zwitterion form at pH=7.4?

 

1. Arg      b. Asp      c.  Pro     d. Glu   e.Lys

 

23. Which of the following amino acids has a fully protonated R group at pH=7.4.

 

1. His    b. Lys   c. Glu   d. Asp   e. none of the above

 

For questions 24-25, refer to the following diagram.

 

 

 

24. What is the name of the bond highlighted?

 

1. Dehydration
2. Peptide bond
3. Zwitterion
4. Glycosidic linkage

 

25. Which of the following is false?

 

1. The amino group is called the N-terminus.
2. The carboxylate group is called the C-terminus.
3. There is resonance in the bond.
4. There is free rotation between the C-N in the peptide bond.
5. None of the above

 

26.Which amino acid is rarely found in an alpha helix?

 

1. methionine
2. glutamate
3. proline
4. none of the above

 

27.Which of the following refers to the amino acid sequence of a protein?

 

1. primary structure
2. secondary structure
3. tertiary structure
4. quaternary structure

 

28.Which of the following refers to all aspects of the three-dimensional folding of a polypeptide?

 

1. primary structure
2. secondary structure
3. tertiary structure
4. quaternary structure

 

29.Which of the following stabilizes the correct protein structure after folding?

 

1. disulfides
2. hydrogen bonds
3. van der waals
4. salt bridges
5. all of the above

 

30.The main factor that explains why proteins fold is

 

1. the stabilization of the protein due to hydrogen bonds.
2. the increase in entropy of the surroundings due to increased randomness of water molecules
3. the formation of covalent bonds between different amino acid residues
4. the decrease in organization when the protein folds
5. none of the above

 

 

For question 31, refer to Diagram A that is attached to the test.

 

31.The diagram above represents

 

1. alpha helix
2. beta sheets
3. beta turn
4. beta barrel
5. collagen helix

 

 

32.Which of the following is true about an alpha helix?

 

1. Many charged amino acids in a successive pattern will stabilize the alpha helix.
2. Bulky R groups on amino acids will stabilize the alpha helix.
3. The polypeptide chain is the backbone for the helix with the R groups protruding outward from this backbone.
4. The structure is stabilized by hydrogen bonds between the H atom attached to the nitrogen atom of a peptide linkage and the carbonyl group of the fourth amino acid on the amino terminal side of the peptide bond.
5. Both c and d

 

33. Which of the following is true for hemoglobin?

 

1. The binding of one oxygen molecule makes it more difficult for the other oxygen molecules to bind.
2. It contains a prosthetic group that contains Ca²⁺ ion.
3. The R state is the high affinity state of the protein.
4. The protein consists of four polypeptide chains that each can bind one molecule of oxygen.
5. Both c and d

 

34. Which of the following is false about myoglobin?

 

1. It is found primarily in muscle tissue.
2. It has a heme group.
3. It consists of 1 polypeptide with eight alpha helical segments
4. It shows a sigmoidal curve for binding oxygen
5. Both c and d

 

Write directly on the exam

 

 

35. The blood is buffered with H₂CO₃ and HCO₃^– according to the following equation:

 

CO₂(g)  + H₂O(l)  <-> H₂CO₃(aq) + H­₂O (l)  <-> H₃O⁺ (aq)  +  HCO₃^–(aq)

                               K₁                                                          K₂

 

1. Write the K expression for the reaction of carbon dioxide and water to form carbonic acid. (K₁).

 

 

 

 

 

1. Write the K expression for the ionization of carbonic acid. (K₂).

 

 

 

 

 

1. Using Le Chatelier’s Principle, explain how the reactions shift when there is increase in CO₂ as occurs in the tissues. How does this affect blood acidity? What does it do to the pH of blood? Explain how the acidity level and pH of the blood changes as CO₂ is expelled in the lungs.

 

 

 

 

 

 

 

 

 

 

36. Write the tripeptide chain for D-A-K at pH=7.4.

 

 

 

 

 

 

 

 

 

 

37. For the amino acid glutamic acid, draw the titration curve (pH vs. Volume of OH^– added) for the amino acid starting at a low pH.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1. Label the three pKa’s on the graph.

 

 

 

 

1. Determine the pH at the first two equivalence points.

 

 

 

 

 

1. What is Zwitterion of the amino acid? Identify the pI.

 

 

 

 

1. Write the structure or structures present at the following pH’s:

 

 

pH=2.13

 

 

 

 

 

 

pH=5.00

 

 

 

 

 

 

pH=10.20

 

 

 

 

 

38a. Draw the graph for the binding of hemoglobin vs. pO₂.

 

 

 

 

 

 

1. Label the regions where the pressure of O₂ are high and low.

 

 

 

 

 

2. Label the region where the hemoglobin in its high affinity state for O₂ or low affinity state for O_2. Is this scenario present in the tissues or lungs? Explain.

 

 

 

 

2. Label the region where the hemoglobin in its high affinity state for O₂ or low affinity state for O_2. Is this scenario present in the tissues or lungs? Explain.

 

 

 

 

To answer e, refer to the following reaction:  CO₂ +  H₂O à H⁺  +  HCO₃^–

 

1. As the [H⁺] increases, the pH ______________. The amount of carbon dioxide ___________

due to _____________ Principle. Carbon dioxide binds to the hemoglobin at different site of the protein. What happens to hemoglobin’s affinity for O₂ when CO₂ bind? Does this scenario happen in the tissues or the lungs? Explain.

 

 

 

 

 

 

 

 

39. What is the role of 2,3-BPG in hemoglobin binding of oxygen?