CHEM 135 MIDTERM EXAM
• London dispersion forces are attractive forces that arise due to
A) infinitesimal dipoles generated by the constant random motion of electrons.
B) permanent dipoles of molecules containing covalent bonds between atomsof very different
electronegativities.
C) the hydrophobic effect.
D) ion pairing between oppositely charged functional groups.: A) Infinitesimaldipoles
generated by the constant random motion of electrons.
• The three dimensional structure of most proteins is largely determined by
A) other proteins which fold them.
B) weak noncovalent interactions.
C) denaturation.
D) hydrogen bonds.
E) All of the above.: B) Weak noncovalent interactions
• The oxygen atom of water is nucleophilic because
A) it has a negative oxidation number.
B) it carries a partial positive charge.
C) it has two unshared pair of electrons.
D) it seeks electron-rich molecules.
E) All of the above.: C) it has two unshared pair of electrons.
• Water is a nucleophile, yet it does not usually hydrolyze macromoleculesin cells because
A) covalent bonds linking macromolecule subunits are stable at cell pH.
B) covalent bonds linking macromolecule subunits are stable at cell temper-ature.
C) the concentration of water is much too small in cells.
D) A and B.: D) A and B.
• What are the 4 levels of protein structure? Describe each level.: 1) Primary
,- amino acid squence
2) Secondary- local, regular pattern
3) Tertiary- how secondary structure pack together
4) Quaternary - how each subunit in a multisubunit protein pack together
• The ion-product constant for water, Kw, isA) 1 × 10-7 M2.
B) 1 × 10-7 M.
C) 1 × 10-14 M2.
D) 1 × 10-14 M.: 1 × 10-14 M2.
• Water molecules clustered about nonpolar molecules contribute to hy-drophobic
interactions because
A) their number is minimized to increase the total entropy of water.
B) nonpolar molecules are more highly organized than polar molecules.
C) water molecules in the cell are more organized in the regions away from thenonpolar
molecule.
D) All of the above.
E) B and C.: A) their number is minimized to increase the total entropy of water.
• The pKa of lactic acid is 3.9. A lactate buffer will be useful from pH values
A) 3.5 through 4.4.
B) 3.0 through 4.5.
C) 2.9 through 4.9.
D) 3.8 through 4.0.: C) 2.9 through 4.9.
• pKa values of phosphoric acid are 2.2, 7.2 and 12.7. A phosphate buffer ofpH = 7.4 can be
prepared using
A) H2PO4- and HPO42-.
B) HPO42- and PO43-.
C) H3PO4 and HCl.
D) None of the above.: B) H2PO4- and HPO42-.
,• Acetic acid has a pKa of 4.8. How many milliliters of 0.2 M acetic acid and
0.2 M sodium acetate are required to prepare 1 liter of 0.1 M buffer solutionhaving a pH of
4.8?
A) 500 ml acetic acid and 500 ml sodium acetate.
B) 250 ml acetic acid and 250 ml sodium acetate, then 500 ml water.
C) 250 ml acetic acid and 500 ml sodium acetate, then 250 ml water.
D) 500 ml acetic acid and 250 ml sodium acetate, then 250 ml water.: B) 250 mlacetic acid and
250 ml sodium acetate, then 500 ml water.
• List the anions in the Hofmeister Series from highest enhance proteinstability, highest
charge density, and highest bound water.: HPO4^-2 SO4^-2
C2H3O2 -F-
Cl-
Br-
I- ClO4-SCN-
• The polarity of small molecules is a result of....
a) the presence of oxygen
b) the geometry of the bonds in the molecule
c) the polar covalent bonds
d) all of the above
e) B and C: e) B and C
• Which statement is true about hydrogen bonds between water molecule?
A) They are about as strong as the covalent bonds in a water molecule
B) They arise because of the linear geometry of water
C) They cause water to have an unusually low freezing point for its molecularweight.
D) They involve the unequal sharing of a proton between water molecules: D)They involve
the unequal sharing of a proton between water molecules
• What is the maximum number of hydrogen bonds that one water moleculecan have with
neighboring water molecules?: 4
, • Which substance do you expect to be most soluble in water?
a) Ammonia, NH3
b) Methane, CH4
c) Carbon dioxide, C02
d) Nitrogen, N2: A) Ammonia, NH3 (because both molecules are polar. polar am-monia
molecules in water facilitated by strong interactions with the polar molecules)
• Which amino acid is unique for its ability to form cross linking disulfidebonds with
another molecule of itself?: Cys
• In the Mercedes-Benz 2-dimensional model of ice, how many perfectH-bonds does each
water molecule make?: 3
• What are some organic compounds?: - alcohol (R-OH)
- aldehyde
- ketone
- carboxylic acid
- thiol
- amine (primary R-NH2, secondary & tertiary)
• What is the concentration of pure water?: 55 M
• What are the four non-covalent weak interactions in biochemistry?: 1. saltbridge (- and + )
• hydrogen bonds
• van der waals interactions (weakest = London dispersion)4.hydrophobic "interaction"
• For ion exchange chromatography, how should the mobile phase be mod-ified to release
the subset of proteins that are most strongly bound to the stationary phase?: Increase the
concentration of NaCl
• Ala-Phe-Met-Val-Ile-Arg-Ala-Lys-Thr-Asp-Leu-Gly
For the polypeptide sequence given above, how many fragments will beobtained if it is
digested...
A) with trypsin?
B) with chymotrypsin?
C) with CNBr?: A) 3
B) 2
• London dispersion forces are attractive forces that arise due to
A) infinitesimal dipoles generated by the constant random motion of electrons.
B) permanent dipoles of molecules containing covalent bonds between atomsof very different
electronegativities.
C) the hydrophobic effect.
D) ion pairing between oppositely charged functional groups.: A) Infinitesimaldipoles
generated by the constant random motion of electrons.
• The three dimensional structure of most proteins is largely determined by
A) other proteins which fold them.
B) weak noncovalent interactions.
C) denaturation.
D) hydrogen bonds.
E) All of the above.: B) Weak noncovalent interactions
• The oxygen atom of water is nucleophilic because
A) it has a negative oxidation number.
B) it carries a partial positive charge.
C) it has two unshared pair of electrons.
D) it seeks electron-rich molecules.
E) All of the above.: C) it has two unshared pair of electrons.
• Water is a nucleophile, yet it does not usually hydrolyze macromoleculesin cells because
A) covalent bonds linking macromolecule subunits are stable at cell pH.
B) covalent bonds linking macromolecule subunits are stable at cell temper-ature.
C) the concentration of water is much too small in cells.
D) A and B.: D) A and B.
• What are the 4 levels of protein structure? Describe each level.: 1) Primary
,- amino acid squence
2) Secondary- local, regular pattern
3) Tertiary- how secondary structure pack together
4) Quaternary - how each subunit in a multisubunit protein pack together
• The ion-product constant for water, Kw, isA) 1 × 10-7 M2.
B) 1 × 10-7 M.
C) 1 × 10-14 M2.
D) 1 × 10-14 M.: 1 × 10-14 M2.
• Water molecules clustered about nonpolar molecules contribute to hy-drophobic
interactions because
A) their number is minimized to increase the total entropy of water.
B) nonpolar molecules are more highly organized than polar molecules.
C) water molecules in the cell are more organized in the regions away from thenonpolar
molecule.
D) All of the above.
E) B and C.: A) their number is minimized to increase the total entropy of water.
• The pKa of lactic acid is 3.9. A lactate buffer will be useful from pH values
A) 3.5 through 4.4.
B) 3.0 through 4.5.
C) 2.9 through 4.9.
D) 3.8 through 4.0.: C) 2.9 through 4.9.
• pKa values of phosphoric acid are 2.2, 7.2 and 12.7. A phosphate buffer ofpH = 7.4 can be
prepared using
A) H2PO4- and HPO42-.
B) HPO42- and PO43-.
C) H3PO4 and HCl.
D) None of the above.: B) H2PO4- and HPO42-.
,• Acetic acid has a pKa of 4.8. How many milliliters of 0.2 M acetic acid and
0.2 M sodium acetate are required to prepare 1 liter of 0.1 M buffer solutionhaving a pH of
4.8?
A) 500 ml acetic acid and 500 ml sodium acetate.
B) 250 ml acetic acid and 250 ml sodium acetate, then 500 ml water.
C) 250 ml acetic acid and 500 ml sodium acetate, then 250 ml water.
D) 500 ml acetic acid and 250 ml sodium acetate, then 250 ml water.: B) 250 mlacetic acid and
250 ml sodium acetate, then 500 ml water.
• List the anions in the Hofmeister Series from highest enhance proteinstability, highest
charge density, and highest bound water.: HPO4^-2 SO4^-2
C2H3O2 -F-
Cl-
Br-
I- ClO4-SCN-
• The polarity of small molecules is a result of....
a) the presence of oxygen
b) the geometry of the bonds in the molecule
c) the polar covalent bonds
d) all of the above
e) B and C: e) B and C
• Which statement is true about hydrogen bonds between water molecule?
A) They are about as strong as the covalent bonds in a water molecule
B) They arise because of the linear geometry of water
C) They cause water to have an unusually low freezing point for its molecularweight.
D) They involve the unequal sharing of a proton between water molecules: D)They involve
the unequal sharing of a proton between water molecules
• What is the maximum number of hydrogen bonds that one water moleculecan have with
neighboring water molecules?: 4
, • Which substance do you expect to be most soluble in water?
a) Ammonia, NH3
b) Methane, CH4
c) Carbon dioxide, C02
d) Nitrogen, N2: A) Ammonia, NH3 (because both molecules are polar. polar am-monia
molecules in water facilitated by strong interactions with the polar molecules)
• Which amino acid is unique for its ability to form cross linking disulfidebonds with
another molecule of itself?: Cys
• In the Mercedes-Benz 2-dimensional model of ice, how many perfectH-bonds does each
water molecule make?: 3
• What are some organic compounds?: - alcohol (R-OH)
- aldehyde
- ketone
- carboxylic acid
- thiol
- amine (primary R-NH2, secondary & tertiary)
• What is the concentration of pure water?: 55 M
• What are the four non-covalent weak interactions in biochemistry?: 1. saltbridge (- and + )
• hydrogen bonds
• van der waals interactions (weakest = London dispersion)4.hydrophobic "interaction"
• For ion exchange chromatography, how should the mobile phase be mod-ified to release
the subset of proteins that are most strongly bound to the stationary phase?: Increase the
concentration of NaCl
• Ala-Phe-Met-Val-Ile-Arg-Ala-Lys-Thr-Asp-Leu-Gly
For the polypeptide sequence given above, how many fragments will beobtained if it is
digested...
A) with trypsin?
B) with chymotrypsin?
C) with CNBr?: A) 3
B) 2
