BIOC 384 ACTUAL FINAL PAPER QUESTIONS AND
ANSWERS GRADED A+
✔✔what does it mean for a molecule to be amphipathic? why are amphipathic lipids
important for life? - ✔✔Amphipathic molecules contain a hydrophobic and hydrophilic
region. they form biological membranes, whose hydrophobic core is relatively
impermeable to polar molecules. this maintains separation of the inside of cells from the
environment and allows compartmentalization within cells where specific rxns can occur
✔✔name and describe four complexes of phospholipids formed in aq environments.
what role does the hydrophobic effect play in the formation of these complexes? - ✔✔1.
phospholipid monolayers have polar head groups pointed toward the water and tails
pointed towards the air
2. phospholipid bilayers form a hydrophobic barrier between 2 aq compartments
3. micelles have hydrophobic tails packed in the center of a sphere and polar head
groups facing outward toward water
4. liposomes are spherical structures bound by a lipid bilayer with an aq center
all these are organized to increase entropy, consistent with the hydrophobic effect
✔✔name and briefly describe the 3 major classes of eukaryotic biological membranes -
✔✔1. the plasma membrane is the lipid bilayer surrounding a cell
2. the endomembrane consists of structurally related intracellular membrane networks
and vesicles
3. cholorplast and mitochondrial membranes enclose enzymes that perform energy
conversions and separate the environment inside these organelles from the cytoplasm
✔✔explain why plants at night can be thought of as animals in terms of the similarities
in their bioenergetic needs - ✔✔plants and animals metabolize nutrients by the process
of anerobic respiration
✔✔how does the 2nd law of thermo apply to energy conversion systems in a living
organism? - ✔✔all natural processes in the universe tend toward dispersal of energy in
the absence of energy input. many biochemical rxns are maintained at a steady state
far from eqilibrium; they use chemical energy to limit entropy and avoid reaching
equilibrium with the environment
✔✔the change in free energy between reactants and products can use used to
determine if a rxn is spontaneous. (a) what is meant by free energy ΔG and ΔG'? (b)
write an eq that describes ΔG' when a rxn is at equilibrium (c) what effects are there on
ΔG, ΔG', or Keq if an enzyme is present in the rxn - ✔✔(a) ΔG' refers to the biochemical
standard free energy change of a rxn. change from initial reactant and product [c] of 1M
each. ΔG is the actual free energy change in a rxn
(b) ΔG' = -RT(ln(B/A))
, (c) enzymes are catalysts and only affect the rates if chemical rxns. they are all
unchanged in the presence of an enzyme
✔✔Keq for the rxn A--B is 1E10^5 at 25 dC. (a) if you started with a solution containing
1.000 M of A and 1 mM or B and let the rxn proceeed to eqilibrium, what would be the
[c] of A and B? (b) calculate the ΔG' (c) in cells at steady state, the [c] of A is 0.05 mM
and the [c] of B is 15mM. Calculate ΔG for the rx A--B - ✔✔(a) Keq = [B] / [A] = 1E10^5.
rearrange to get [B] = 100,000[A]. the total number of moles of A plus B must stay
constant throughout the rxn. [A] + [B] = 1.000M + 0.001M = 1.001M and now [A] +
100,000[A] = 1.001M. [A] = 1.000989E^-5M and thus [B] = 1.000989M
(b) ΔG =ΔG' + RTln(Q) = 0; ΔG' = -(8.3E10^-3)(298)ln(1E10^5) = -28.5 kJ/mol
(c) ΔG =ΔG' + RTln(Q); ΔG = -28.5 + (8.3E10^-3)(298)ln(1.5E10^-E10^-5) = -28.5 +
14.1 = -14.4 kJ/mol
✔✔the EC of a cell reflects the amount of phosphoryl transfer energy available from
ATP. the levels of ATP, ADP, and AMP in a cell are maintained in part by the adenylate
kinase rxn, which interconverts ATP + AMP -- ADP + ADP.
(a) calculate the EC in a cultured cancer cell line found to have the following: 1.25 mM
ATP, 0.35 mM ADP, and 0.12 mM AMP
(b) what is the Keq of the rxn ? - ✔✔(a) EC = [ATP] + 0.5[ADP] / [ATP] + [ADP] +
[AMP]; EC = 0.83
(b) Keq = [ADP][ADP]/[ATP][AMP] = 0.81
✔✔explain how EC affects metabolic flux through anabolic and catabolic pathways -
✔✔the EC of the cell refers to the relative [c] of ATP, ADP, and AMP. at high EC, ATP
[c] are high relative to AMP and ADP. Anabolic pathways require ATP, so a high EC
leads to increased flux through anabolic pathways. In contrast, at low EC, flux is
increased through catabolic pathways to replenish ATP levels
✔✔Why is entropy negative when a nonploar molecule (like limonene) is dissolved in
H2O? - ✔✔the H2O molecules H-bond inot a cage-like structure around the
hydrophobic limonene, increasing the order of the H2O molecules. this is entropically
unfavorable and therefor entropy is negative
✔✔in solid NaCl, both the Na and the Cl ions are held in a rigid crystalline lattice and
are immobile in an electric field. Ice also forms a lattice structe; however, in the
presence of an electric field, significant proton mobility occurs in ice. explain - ✔✔H2O
molecules in ice are oriented such that maximum H-bonding between H2O molecules
occurs. protons move through ice and water via proton hopping
✔✔name the 4 noncovalent interactions. which of these directly or indirectly involve
H2O molecules? - ✔✔1. H-bonds
2. ionic interactions
3. van der Waals interactions
4. hydrophobic effect
ANSWERS GRADED A+
✔✔what does it mean for a molecule to be amphipathic? why are amphipathic lipids
important for life? - ✔✔Amphipathic molecules contain a hydrophobic and hydrophilic
region. they form biological membranes, whose hydrophobic core is relatively
impermeable to polar molecules. this maintains separation of the inside of cells from the
environment and allows compartmentalization within cells where specific rxns can occur
✔✔name and describe four complexes of phospholipids formed in aq environments.
what role does the hydrophobic effect play in the formation of these complexes? - ✔✔1.
phospholipid monolayers have polar head groups pointed toward the water and tails
pointed towards the air
2. phospholipid bilayers form a hydrophobic barrier between 2 aq compartments
3. micelles have hydrophobic tails packed in the center of a sphere and polar head
groups facing outward toward water
4. liposomes are spherical structures bound by a lipid bilayer with an aq center
all these are organized to increase entropy, consistent with the hydrophobic effect
✔✔name and briefly describe the 3 major classes of eukaryotic biological membranes -
✔✔1. the plasma membrane is the lipid bilayer surrounding a cell
2. the endomembrane consists of structurally related intracellular membrane networks
and vesicles
3. cholorplast and mitochondrial membranes enclose enzymes that perform energy
conversions and separate the environment inside these organelles from the cytoplasm
✔✔explain why plants at night can be thought of as animals in terms of the similarities
in their bioenergetic needs - ✔✔plants and animals metabolize nutrients by the process
of anerobic respiration
✔✔how does the 2nd law of thermo apply to energy conversion systems in a living
organism? - ✔✔all natural processes in the universe tend toward dispersal of energy in
the absence of energy input. many biochemical rxns are maintained at a steady state
far from eqilibrium; they use chemical energy to limit entropy and avoid reaching
equilibrium with the environment
✔✔the change in free energy between reactants and products can use used to
determine if a rxn is spontaneous. (a) what is meant by free energy ΔG and ΔG'? (b)
write an eq that describes ΔG' when a rxn is at equilibrium (c) what effects are there on
ΔG, ΔG', or Keq if an enzyme is present in the rxn - ✔✔(a) ΔG' refers to the biochemical
standard free energy change of a rxn. change from initial reactant and product [c] of 1M
each. ΔG is the actual free energy change in a rxn
(b) ΔG' = -RT(ln(B/A))
, (c) enzymes are catalysts and only affect the rates if chemical rxns. they are all
unchanged in the presence of an enzyme
✔✔Keq for the rxn A--B is 1E10^5 at 25 dC. (a) if you started with a solution containing
1.000 M of A and 1 mM or B and let the rxn proceeed to eqilibrium, what would be the
[c] of A and B? (b) calculate the ΔG' (c) in cells at steady state, the [c] of A is 0.05 mM
and the [c] of B is 15mM. Calculate ΔG for the rx A--B - ✔✔(a) Keq = [B] / [A] = 1E10^5.
rearrange to get [B] = 100,000[A]. the total number of moles of A plus B must stay
constant throughout the rxn. [A] + [B] = 1.000M + 0.001M = 1.001M and now [A] +
100,000[A] = 1.001M. [A] = 1.000989E^-5M and thus [B] = 1.000989M
(b) ΔG =ΔG' + RTln(Q) = 0; ΔG' = -(8.3E10^-3)(298)ln(1E10^5) = -28.5 kJ/mol
(c) ΔG =ΔG' + RTln(Q); ΔG = -28.5 + (8.3E10^-3)(298)ln(1.5E10^-E10^-5) = -28.5 +
14.1 = -14.4 kJ/mol
✔✔the EC of a cell reflects the amount of phosphoryl transfer energy available from
ATP. the levels of ATP, ADP, and AMP in a cell are maintained in part by the adenylate
kinase rxn, which interconverts ATP + AMP -- ADP + ADP.
(a) calculate the EC in a cultured cancer cell line found to have the following: 1.25 mM
ATP, 0.35 mM ADP, and 0.12 mM AMP
(b) what is the Keq of the rxn ? - ✔✔(a) EC = [ATP] + 0.5[ADP] / [ATP] + [ADP] +
[AMP]; EC = 0.83
(b) Keq = [ADP][ADP]/[ATP][AMP] = 0.81
✔✔explain how EC affects metabolic flux through anabolic and catabolic pathways -
✔✔the EC of the cell refers to the relative [c] of ATP, ADP, and AMP. at high EC, ATP
[c] are high relative to AMP and ADP. Anabolic pathways require ATP, so a high EC
leads to increased flux through anabolic pathways. In contrast, at low EC, flux is
increased through catabolic pathways to replenish ATP levels
✔✔Why is entropy negative when a nonploar molecule (like limonene) is dissolved in
H2O? - ✔✔the H2O molecules H-bond inot a cage-like structure around the
hydrophobic limonene, increasing the order of the H2O molecules. this is entropically
unfavorable and therefor entropy is negative
✔✔in solid NaCl, both the Na and the Cl ions are held in a rigid crystalline lattice and
are immobile in an electric field. Ice also forms a lattice structe; however, in the
presence of an electric field, significant proton mobility occurs in ice. explain - ✔✔H2O
molecules in ice are oriented such that maximum H-bonding between H2O molecules
occurs. protons move through ice and water via proton hopping
✔✔name the 4 noncovalent interactions. which of these directly or indirectly involve
H2O molecules? - ✔✔1. H-bonds
2. ionic interactions
3. van der Waals interactions
4. hydrophobic effect
