Unit 1 - Lecture Quizzes Flashcards
what is the enthalpy ot a chemical reaction that is spontaneous at 3/°C and has an entropy change of 35 J^-1mol^-1?
a) 5.6 kJ/mol
b) 10.8 kJ/mol
c) 35 kJ/mol
d) 62.4 kJ/mol
e) Not enough information is given to answer this question.
e) Not enough information is given to answer this question.
For a given reaction, 18.6 kJ × mol^-1 of heat is absorbed and the change in entropy is 62 J × K^-1 × mol^-1. What is the lowest temperature above which the reaction will be spontaneous?
a) 43 k
b) 294 K
c) 300 K
d) 3K
e) 308 k
c) 300 K
Which of the following statements is false?
a) Hydrogen bonding strength depends on the orientation of the atoms involved
b) lonic interactions are stronger in non-polar environments than in polar
environments.
c) Ionic interactions do not depend on the relative orientation of the ions
d) Hydrogen bonds are weaker than covalent bonds
e) Van der Waals interactions are too weak to be a significant attractive force.
e) Van der Waals interactions are too weak to be a significant attractive force.
Which one of the following is NOT an example of a hydrogen bond?
a) -C-H—–O
b) -O-H—–N
c) -N-H—– O
d) -N-H—–N
e) -O-H——O
a) -C-H—–O
Which molecule would you expect to be non-polar?
A. H2O
B. CO2
C. NH3
D. CHCl3
E. These molecules have equal polarity
B. CO2
For a chemical reaction, if the change in enthalpy is negative and the change in entropy is positive, the reaction will be:
A. Never spontaneous
B. Always spontaneous
C. Sometimes spontaneous
D. Not enough information is given
B. Always spontaneous
Which compound is the most acidic?
A. Acetic acid (pKa = 4.76)
B. Trifluoroacetic acid ( pKa = 0.18)
C. Phosphate (pKa = 6.82)
D. Boric acid (pKa=9.24)
E. Sodium hydroxide
B. Trifluoroacetic acid ( pKa = 0.18)
If your kidneys are unable to function properly, you may expect to have:
A. Decreased levels of HCO 3- in the blood, resulting in a decrease of blood pH
B. Increased levels of HCO 3- in the blood, resulting in a decrease of blood pH
C. Decreased levels of HCO 3- in the blood, resulting in an increase of blood pH
D. Decreased levels of HCO 3- in the blood, resulting in an increase of CO 2 concentration
E. None of the above
A. Decreased levels of HCO 3- in the blood, resulting in a decrease of blood pH
Note:
- Equilibrium shifts left due to insufficient HCO 3- (renal problems) or high CO 2 (poor lung function)
A solution contains a typical protein containing many acidic and basic amino acid residues. If the pH of the solution is less than the pI of the protein:
A. The protein will tend to be deprotonated, causing it to have a net positive charge
B. The protein will tend to be protonated, causing it to have a net positive charge
C. The protein will tend to be deprotonated, causing it to have a net negative charge
D. The protein will tend to be protonated, causing it to have a net negative charge
E. The protein will have a net charge of 0.
B. The protein will tend to be protonated, causing it to have a net positive charge
What is the approximate isoelectric point of the following hexapeptide. Consult your notes to obtain relevant pKa values.
Asp-Leu-Ile-Glu-Lys-Gly?
Which of these statements about protein folding is
false?
A. The native state is stabilized by the high entropy of water (hydrophobic effect)
B. The native state is destabilized by the low entropy of protein
C. Certain residue orientations (phi/psi angles) are more favourable than others
D. When folding, a protein samples all possible conformations to find the native state
E. The native state is stabilized by favourable enthalpic interactions, such as hydrogen bonds
D. When folding, a protein samples all possible conformations to find the native state
..false, proteins don’t randomly test of states they are guided through various conformations that are unstable until it finds stable structure..
Which DNA sequence would you expect to have the
highest melting temperature?
A. GCCGCGGCCCGG
B. ATCAATACTTAT
C. GCAACTACTGCA
D. AACCTTGGAAAG
E. Not enough information is given
A. GCCGCGGCCCGG
Which of the following mutations cannot result in a
frameshift?
A. Insertion
B. Deletion
C. Substitution
D. Dinucleotide repeat expansion
E. All of these mutations can results in a frameshift
C. Substitution
What would be the resulting pH if one drop (0.05 ml) of 1.0 M HCI were added to one liter of pure water (assume initial pH 7.0?
a) 2.7
b) 4.3
c) 5.0
d) 9.7
e) 7.0 (there would be no significant change)
b) 4.3
What is the resulting pH if 1 mL of 10 M HCI is added to 1 liter of 0.1 M sodium phosphate buffer (pH 7.00). The pKa of sodium phosphate is 6.82.
a) 6.82
b) 6.98
c) 7.01
d) 7.19
e) Cannot be determined
a) 6.82
Which of the below statements is false?
a) Bicarbonate is an important extracellular buffer.
b) A buffer is the least effective when the solution pH is the same as the buffer’s pKa.
c) Phosphate is an important intracellular buffer.
d) Many biomolecules can behave as buffers.
e) Le Chatelier’s principle is important for pH regulation in the body.
b) A buffer is the least effective when the solution pH is the same as the buffer’s pKa.
…false, that’s when its most effective..
Which of the below statements is false?
a) A buffer is the most effective when the solution pH is the same as the buffer’s pKa.
b) In aqueous solutions the concentration of OH and H* is always equal to 10-7 M.
c) Carbon, nitrogen, oxygen, and hydrogen are some of the most abundant elements in living things.
b) In aqueous solutions the concentration of OH and H* is always equal to 10-7 M.
..Its actually equal to 10^14M…
What would be the resulting pH if one drop (0.05 ml) of 1.0 M HCI were added to one liter of pure water (assume initial pH 7.0)?
a) 2.7
b) 4.3
c) 5.0
d) 9.7
e) 7.0 (there would be no significant change)
b) 4.3
Why?
- As HCI is a strong acid, the final concentration of (H*] would be the same as the concentration of HCI added, i.e. 1.0 M × (0.05 ml)(1000 ml) = 5x10-S M. Taking the negative log, the pH would be 4.3.
What is the resulting pH if 1 mL of 10 M HCI is added to 1 liter of 0.1 M sodium phosphate buffer (pH 7.00). The pKa of sodium phosphate is 6.82.
a) 6.82
b) 6.98
c) 7.01
d) 7.19
e) Cannot be determined
a) 6.82
Why?
- Initially, 7.00 = 6.82 + log(HPO42-1/H-PO4 )), thus [HPO47-11H2P04] = 1.51.
- Since the total buffer concentration (HPO43-1+(H,PO4] = 0.1 M, then solving for (HPO-j: 0.1 M = (H-PO41+
(1.51)(HPO42-J, thus [HyPO4] = 0.IM/2.51 = 0.04 M, or 0.04 mol in 1 litre. Thus, [HPO42-J= 0.1 - 0.04 = 0.06 M
(0.06 mol in 1 litre).
- Adding 10 mmol (0.01 mol) of HCI will titrate that amount of (HO 2- to [HyPO4 1, so the final ratio will be (0.06-0.01)/(0.04+0.01) = 0.05/0.05 = 1.
- Since log(1) = 0, the final pH will be 6.82 (which happens to be equal to the pK).
The hydrophobic effect is largely responsible for correct protein folding and the association of lipids into bilayers and other structures. The basis of the hydrophobic effect is:
a) Increased dielectric constant of water relative to non-polar solvents.
b) Increased water entropy due to minimized contact of water with non-polar groups.
c) Increased hydrogen bonding in water molecules surrounding non-polar molecules.
d) Vibration of water molecules adjacent to non-polar molecules.
e) Attraction of closely packed non-polar groups due to van der Waals interactions.
b) Increased water entropy due to minimized contact of water with non-polar groups.
The side chain of aspartic acid normally has a pK of 3.9. At which pH value would you expect about 90% of the Asp side chains to be in the negatively charged (COO) form?
a) рн 2.9
b) рн 3.9
c) pH 4.9
d) рн 5.9
e) pH 8.6
c) pH 4.9
Why?
- According to the Henderson-Hasselbalch equation, the value of log[A*J/ [HA] would be +1 when the ratio of [A”/[HA] is 10, or about 90% of Asp side chains in the carboxylate form, corresponding to a pH value one unit above the pK.
Only the amino acid can spontaneously form covalent bonds between two different polypeptide chains, while
is often used to monitor protein purification because of its ability to absorb ultraviolet light.
a) proline; tyrosine
b) cysteine, tryptophan
c) methionine; cysteine
d) glutamic acid; valine
e) methionine, histidine
b) cysteine, tryptophan
Why?
- When oxidized, two cysteine residues can form a disulfide bond between (or within) polypeptide chains, while tryptophan has the highest UV absorbance of all the amino acids (at 280 m).
What is the approximate net charge of the pentapeptide Ala-Arg-Ser-Glu-Asn at pH 7?
a) -2
b) -1
c) 0
d) +1
e) +2
c) 0
Why?
- At this pH, the charged groups will consist of the N-terminal amino group (+), the guanidinium side chain of Arg (+), the Glu carboxyl side chain (-), and the C-terminal carboxy group (-). Note that peptide bonds are not charged. Thus, the net charge of the peptide is zero, as these all cancel out. N.B. while you are not expected to memorize exact pK values, you should know the amino acid side chain structures and thus which are negative, neutral, and positive at pH 7.
What is the approximate isoelectric point of the following hexapeptide. Consult your notes to obtain relevant pKa values.
Asp-Leu-lle-Glu-Lys-Gly?
a) 3.7
b) 4.0
c) 6.55
d) 9.75
b) 4.0
Why?
- There are 5 protons that can be dissociated from this functional group (the side chains of Asp, Glu, and Lys, as we as the N- and C- terminus).
- The isoelectric point of this peptide is enclosed by two pa values (3.9 and 4.1). The average of these two values is 4.0, which is the isoelectric point.