Introduction to Biochemistry Questions

Introduction to BiochemistryOld Exam Questions
Dr. Gustin
Exam 1
1. Which of the following only hydrogen bonding as its strongest intermolecular force?
a.
b.
c.
d.
e.
CH4
CH3NH2
HI
HCl
All except d
2. Which of the following is hydrophobic?
a.
b.
c.
d.
e.
CH3OH
CH2NH2
C8H18
NaCl
All except d
3. Which of the following is true at equilibrium for a weak acid such as HC2H3O2(aq) at 25oC?
HC2H3O2(aq) + H2O(l) H3O+(aq) + C2H3O2-(aq)
a.
b.
c.
d.
There are equal amounts of acid and ions at equilbrium.
There is more HC2H3O2(aq) than H3O+(aq) and C2H3O2-(aq) at equilibrium.
There is more H3O+ and C2H3O2- than HC2H3O2 at equilibrium.
Ka for the acid is very large.
4. Which is the best buffer solution for resisting pH changes at 4.00?
Buffer solution 1:
Buffer solution 2:
Buffer solution 3:
Buffer solution 4:
a.
b.
c.
d.
H3PO4/H2PO4H2CO3/HCO3NH3/NH4+
HF/F-
pKa = 2.14
pKa = 6.35
pKa=9.25
pKa = 3.17
Solution 1
Solution 2
Solution 3
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?
a.
b.
c.
d.
e.
2.3
5.0
7.5
10.0
13.0
6. Which species exists at pH=10.0?
a.
b.
c.
d.
H2A
HAA250% HA- and A2-
7. What is approximately pKa2 of the acid?
a.
b.
c.
d.
e.
2.3
5.0
7.5
10.0
13.0
8. Which of the following is the conjugate base of H2PO4-?
a.
b.
c.
d.
e.
H2PO4HPO42PO43H3PO4
None of the above
9. Which acid is the strongest of the following choices?
H3PO4
H2CO3
NH3
HF
pKa = 2.14
pKa = 6.35
pKa=9.25
pKa = 3.17
a. 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
10. Removal of glucose 6-phosphate will cause
a. the reaction to shift right
b. the reaction to shift left
c. the reaction to stop
d. the reaction form more reactant
11. The ΔG for the reaction is -7.5 kJ/mol. What is true about the reaction?
a.
b.
c.
d.
The reaction is not spontaneous.
The reaction requires free energy.
The reaction is spontaneous.
The reaction favors the formation of glucose 1-phosphate.
12. Which of the following are buffered solution that will have pH=pKa?
a.
b.
c.
d.
e.
3.0 M HCl
3.0 M HC2H3O2 + 3.0 M C2H3O21.0 M HC2H3O2 + 3.0 M C2H3O22. 0 M HC2H3O2 + 3.0 M C2H3O2All 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 ____________.
a.
b.
c.
d.
Endothermic
Endergonic
Exothermic
Exergonic
14.If the ΔH=0 and if the entropy of the system increases, ΔG will be
a.
b.
c.
d.
Negative and free energy will be released.
Positive and free energy will be released.
Positive and free energy will be required.
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?
a.
b.
c.
d.
The strongest intermolecular force in the molecule is van der waals forces.
Glucose can hydrogen bond with water and it is water soluble.
Glucose is a carboxylic acid.
Glucose is non-polar.
17. Which of the following is true about amino acids?
a.
b.
c.
d.
e.
All amino acids are essential.
At pH=7.00, all amino acids are in Zwitterion form.
Amino acids in proteins are found in the D configuration.
There are 22 amino acids.
All amino acids except glycine are chiral.
18. Which of the following amino acids has a hydrophobic side chain?
a. 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?
a. Ser
b. Ala c. Leu
d. Phe
e. Ile
.
20. Which of the following amino acids has an acidic R group?
a. Lys
b. Arg
c. His d. Asp e. Trp
21. Which amino acid can form disulfide linkages?
a. 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?
a. 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.
a. 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?
a.
b.
c.
d.
Dehydration
Peptide bond
Zwitterion
Glycosidic linkage
25. Which of the following is false?
a.
b.
c.
d.
e.
The amino group is called the N-terminus.
The carboxylate group is called the C-terminus.
There is resonance in the bond.
There is free rotation between the C-N in the peptide bond.
None of the above
26.Which amino acid is rarely found in an alpha helix?
a.
b.
c.
d.
methionine
glutamate
proline
none of the above
27.Which of the following refers to the amino acid sequence of a protein?
a.
b.
c.
d.
primary structure
secondary structure
tertiary structure
quaternary structure
28.Which of the following refers to all aspects of the three-dimensional folding of a polypeptide?
a.
b.
c.
d.
primary structure
secondary structure
tertiary structure
quaternary structure
29.Which of the following stabilizes the correct protein structure after folding?
a.
b.
c.
d.
e.
disulfides
hydrogen bonds
van der waals
salt bridges
all of the above
30.The main factor that explains why proteins fold is
a.
b.
c.
d.
e.
the stabilization of the protein due to hydrogen bonds.
the increase in entropy of the surroundings due to increased randomness of water molecules
the formation of covalent bonds between different amino acid residues
the decrease in organization when the protein folds
none of the above
For question 31, refer to Diagram A that is attached to the test.
31.The diagram above represents
a.
b.
c.
d.
e.
alpha helix
beta sheets
beta turn
beta barrel
collagen helix
32.Which of the following is true about an alpha helix?
a.
b.
c.
d.
e.
Many charged amino acids in a successive pattern will stabilize the alpha helix.
Bulky R groups on amino acids will stabilize the alpha helix.
The polypeptide chain is the backbone for the helix with the R groups protruding outward from this
backbone.
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.
Both c and d
33. Which of the following is true for hemoglobin?
a.
b.
c.
d.
e.
The binding of one oxygen molecule makes it more difficult for the other oxygen molecules to
bind.
It contains a prosthetic group that contains Ca2+ ion.
The R state is the high affinity state of the protein.
The protein consists of four polypeptide chains that each can bind one molecule of oxygen.
Both c and d
34. Which of the following is false about myoglobin?
a.
b.
c.
d.
e.
It is found primarily in muscle tissue.
It has a heme group.
It consists of 1 polypeptide with eight alpha helical segments
It shows a sigmoidal curve for binding oxygen
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
a. Write the K expression for the reaction of carbon dioxide and water to form carbonic
acid. (K1).
b. Write the K expression for the ionization of carbonic acid. (K2).
c. 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.
pH
Volume of NaOH
(mL)
a. Label the three pKa’s on the graph.
b. Determine the pH at the first two equivalence points.
c. What is Zwitterion of the amino acid? Identify the pI.
d. 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.
b. Label the regions where the pressure of O2 are high and low.
c. Label the region where the hemoglobin in its high affinity state for O2 or low affinity state for
O2. Is this scenario present in the tissues or lungs? Explain.
d. Label the region where the hemoglobin in its high affinity state for O2 or low affinity state for
O2. Is this scenario present in the tissues or lungs? Explain.
To answer e, refer to the following reaction: CO2 + H2O → H+ + HCO3e. 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?