Quiz 2 Flashcards
All of the following are important for enzyme-substrate interactions EXCEPT
A) hydrogen bonds
B) ionic interactions
C) van der waals interactions
D) covalent bonds
D) covalent bonds
NOTE: Covalent bonds are important for linking the monomers of biomolecules, such as nucleic acids and proteins. More complex intramolecular and intermolecular interactions need to be reversible and weaker to allow for flexibility. Hydrogen bonds, ionic interactions, and van der Waals interactions are weaker interactions.
For ATP (shown below), cleavage of the bond between __________ has the largest ΔG°′.
A) adenine and ribose
B) ribose and a phosphate
C) a phosphate and B phosphate
D) B phosphate and y phosphate
C) a phosphate and B phosphate
NOTE: The phosphoanhydride linkages between the phosphate groups of ATP have high potential energy and result in the largest ΔG°′ values. The bond between the α and β phosphate is slightly more energetic because the resulting pyrophosphate is stabilized by resonance and also still contains an energetic phosphoanhydride bond.
For the reaction: A + B ↔ C + D, which of the following is correct?
A) Keq = [C][D]/[A][B]
B) Keq = [A][B]/[C][D]
C) ΔG° = -RT log Keq
D) ΔG° = RT ln Keq
A) Keq = [C][D]/[A][B]
NOTE: Keq, or the equilibrium constant, is the ratio of products to reactants at equilibrium. The standard free energy change is related to Keq via the equation ΔG° = -RT ln Keq.
If a cell is placed in a hypotonic solution, then
A) water will flow into the cell
B) water will flow out of the cell
C) solutes in the solution will enter the cell
D) there will be no net change in flow of water into or out of the cell
A) water will flow into the cell
NOTE: When a cell is placed in a hypotonic solution, the solution contains fewer solutes than the cell. To compensate and relieve the osmotic pressure, water will enter the cell to equilibrate the solute concentrations. The flow of too much water into the cell can lead the cell to burst. Hypertonic solutions lead to water flowing out of the cell to compensate for the unequal solute concentrations. Solutes are not being exchanged as freely as water. An isotonic solution is completely balanced and thus there is no known net change in water volume.
in the figure below, where is a hydrogen bond acceptor located?
A) A
B) B
C) C
D) D
C) C
NOTE:Water can be a hydrogen bond donor or acceptor, depending on its interaction with which molecule. Oxygen and nitrogen are both hydrogen bond acceptors, while hydrogen attached to nitrogen or oxygen can be donated.
In which case will a reaction be spontaneous only above a certain temperature according to the Gibbs free energy equation?
A) ΔH < 0; ΔS > 0
B) ΔH > 0; ΔS < 0
C) ΔH < 0; ΔS < 0
D) ΔH > 0; ΔS > 0
D) ΔH > 0; ΔS > 0
NOTE: The Gibbs free energy change (ΔG) is a way to determine if a chemical reaction is spontaneous under a particular set of conditions. It takes into account the enthalpy (ΔH), the entropy (ΔS), and temperature, as seen in the equation ΔG = ΔH – TΔS. When ΔH is negative and ΔS is positive, a reaction is spontaneous at all temperatures. In the opposition situation, a reaction is never spontaneous at all temperatures. If ΔH is negative and ΔS is negative, the reaction is only spontaneous when T is less than ΔH/ΔS. If ΔH is positive and ΔS is positive, the reaction is only spontaneous when T is greater than ΔH/ΔS.
The following molecules participate in oxidation-reduction reactions EXCEPT
A) plastoquinone.
B) ATP.
C) NAD+.
D) FADH2.
B) ATP.
NOTE: Plastoquinone, NAD+, and FADH2 undergo oxidation and reduction, which allows them to serve as electron carriers. ATP is an energy carrier in cells, but does not participate in redox reactions.
What is the concentration of [OH-] in a solution of 0.025 M HCl?
A) 2.5 × 10-2 M
B) 4.0 × 10-13 M
C) 1.0 × 10-14 M
D) 4.1 × 10-13 M
B) 4.0 × 10-13 M
NOTE: HCl is a strong acid, which means it will completely dissociate in water. This means the concentration of H+ will be equal to the concentration of HCl, or 0.025 M in this case. The concentration of OH- is related to the concentration of H+ via the water ionization constant, Kw. The concentration of OH- is equal to Kw/[H+].
When a protein enzyme folds in an aqueous solution, which of the following is correct?
A) Water is always excluded from the active site in the interior of the protein.
B) Polar amino acids are found in the interior of the protein.
C) Non-polar amino acids are found in the interior of the protein.
D) A mixture of polar and non-polar amino acids is found in the interior of the protein.
C) Non-polar amino acids are found in the interior of the protein.
NOTE: A major driving force for protein folding is the burying of non-polar amino acids in the interior of the protein to avoid interactions between these hydrophobic amino acids and water. Polar amino acids are typically found on the exterior of the protein. Water is not always completely excluded from the interior of a protein and can play an important role in the active site of an enzyme.
Which membrane structure is only found in plants?
A) Plasma membrane
B) Endomembranes
C) Inner membrane cristae
D) Thylakoid membrane
D) thylakoid membrane
NOTE: All cells are surrounded by a plasma membrane. Endomembranes are important for exchanging materials via vesicles. These membranes also interconnect various organelles in the eukaryotic cell. The inner membrane cristae are found in mitochondria. Thylakoids are unique to chloroplasts and are thus only found in plants.
Which of the following differentiates the biochemical standard state from the standard state when discussing standard free energy changes?
A) Constant pressure of 1 atm
B) Temperature of 298 K
C) 1 M concentrations for all reactants and products
D) pH of 7
D) pH of 7
NOTE: Biological systems operate near the standard state conditions of 1 atm and 298 K. Standard state conditions could be at different pH values, depending on the reactants involved. Biological systems operate at near neutral conditions, so the biological standard state is defined for pH 7.
Which of the following is an example of a heterotroph?
A) Yeast
B) Plants
C) Single-cell algae
D) Cyanobacteria
A) yeast
NOTE: Heterotrophs are unable to convert solar energy into chemical energy directly. Yeast is not capable of photosynthesis and is a heterotroph. Plants, single-cell algae, and photosynthetic bacteria like cyanobacteria are autotrophs capable of converting solar energy into chemical energy.
Which of the following is an example of a weak acid?
A) HCl
B) NaOH
C) Vinegar, CH3COOH
D) Ammonia, NH3
C) Vinegar, CH3COOH
NOTE: HCl and NaOH completely dissociate in water and are examples of a strong acid and a strong base, respectively. Weak acids and bases only partially dissociate in water. Vinegar, or acetic acid, is an example of a weak acid. Ammonia is an example of a weak base.
Which of the following is correct about biological membranes?
A) Biological membranes are made up of a lipid monolayer.
B) Phospholipid tails are directed toward the aqueous environment.
C) Phospholipid head groups are directed toward the aqueous environment.
D) Molecules freely pass through the membrane.
C) Phospholipid head groups are directed toward the aqueous environment.
NOTE: Biological membranes are lipid bilayers, with the polar head groups directed toward the aqueous environments contained within the cell and outside the cell. The tails are directed toward the middle of the bilayers, forming a barrier that does not allow for free movement of molecules across the membrane.
Which of the following is correct concerning the first law of thermodynamics in biological systems?
A) ΔH < 0 for endothermic reactions.
B) ΔH > 0 for exothermic reactions.
C) Pressure and volume do not change.
D) The value of ΔH for a particular reaction depends on the path taken.
C) Pressure and volume do not change.
NOTE: H, or enthalpy, is a state function, so ΔH is independent of the path taken. ΔH is positive for endothermic reactions and negative for exothermic reactions. In biological systems, the pressure and volume do not change.
