BCH4024 EXAM 1 QUESTIONS
WITH CORRECT ANSWERS
Hydrogen Bonds
Strengths of Noncovalent Interactions - Answer- Intrinsically polar interaction
R-N-H•••••O=C-R
(acid base reaction)
requires proton donor(EP) and proton acceptor (EN)
linear bond=strong H bond
bent bond=weak H bond
ΔG ≈ 4 - 40 kJ/mol
Electrostatic
Strengths of Noncovalent Interactions - Answer- Opposite Charges Attract
& Like Charges Repel
ΔG ≈ 4 - 40 kJ/mol
Salt bridge
Strengths of Noncovalent Interactions - Answer- H-bonding + Electrostatics
e.g. carboxylate (R-COO-) i protonated amine (R-NH3+)
ΔG ≈ 40 - 400 kJ/mol
Hydrophobic interactions
Strengths of Noncovalent Interactions - Answer- Displacement of water is driven by
favorable entropy
ΔG ≈ 0.4 - 4 kJ/mol
Pi stacking
Strengths of Noncovalent Interactions - Answer- Stacking of aromatic rings
greater e- delocalization
ΔG ≈ 0.4 - 4 kJ/mol
van der Waals interactions
Strengths of Noncovalent Interactions - Answer- Very weak forces between oscillating
dipoles.
,ΔG ≈ 0.4 - 4 kJ/mol
Hydrogen Bonds
are found throughout Nature - Answer- between peptide groups in polypeptides
between complementary bases of DNA (T+A)
the properties
of the universal solvent
improve solubility
Essential for biospecific recognition.
Easy to make & break (allows fast kinetics)
what are "NOT true bonds" - Answer- No overlapping of atomic or molecular orbitals
The Gibbs Equation - Answer- (ΔG = ΔH - TΔS)
Contrary to intuition, water binds tightly to apolar groups, such
that ΔHwater-binding << 0 (conversely: ΔHwater-release >> 0).
Hydrophobic interaction results in release of water molecules
increases randomness: ΔSwater-release >> 0.
Hydrophobic Interactions - Answer- The Gibbs Equation (ΔG = ΔH - TΔS) is guiding
Strictly speaking, these stabilizing interactions are NOT true bonds
Temperature strongly influences ΔG
Temperature strongly influences ΔG under Hydrophobic Interactions - Answer- At low T
(5-10oC), ΔG = ΔH - TΔS > 0: Unfavorable interaction
At higher T (37oC), ΔG = ΔH - TΔS < 0: Favorable interaction
Hydrophobic groups facilitate protein folding - Answer- protein folding
water release
Side-chains participating in hydrophobic interactions can swivel with ease, thereby
facilitating protein folding.
no orbital overlap occurs in Hydrophobic interactions. strength of int. is unaffected by
geometric considerations
, equally stable interactions
The great variety of hydrophobic side-chains maximizes packing within protein, thereby
maximizing release of bound water.(Ala,Val,Leu,Ile,Try,Tyr)
Hydrophobic interactions stabilize proteins - Answer- Strength of hydrophobic
interaction is determined by the
number of water molecules released per interaction.
Hydrophobic interactions also play dominant role in stabilizing membrane bilayer
structure.
For integral membrane proteins, hydrophobic groups are on the surface and interact
with apolar lipid side-chains of the inner membrane bilayer.
"Water Accessible Area"
"Water Accessible Area" - Answer- is a measure of the number of water molecules
needed to cover a particular hydrophobic side-chain
Behavior of Amphipathic Compounds in Aqueous Solution - Answer- flickering clusters
of H2O molecules in bulk phase
high ordered H2O molecules form cages around Hydrophobic alkyl chains
Amphipathic
molecule
Long-chain fatty acids
Long-chain fatty acids - Answer- have very hydrophobic alkyl chains, each of which is
surrounded by a layer of highly ordered water molecules.
Amphipathic
molecule - Answer- hydrophilic region
(water-like, polar or charged)
hydrophobic region (apolar)
Amphipathic Molecules in Water - Answer- - By clustering together in micelles, the fatty
acid molecules reduce the hydrophobic surface area exposed to water
WITH CORRECT ANSWERS
Hydrogen Bonds
Strengths of Noncovalent Interactions - Answer- Intrinsically polar interaction
R-N-H•••••O=C-R
(acid base reaction)
requires proton donor(EP) and proton acceptor (EN)
linear bond=strong H bond
bent bond=weak H bond
ΔG ≈ 4 - 40 kJ/mol
Electrostatic
Strengths of Noncovalent Interactions - Answer- Opposite Charges Attract
& Like Charges Repel
ΔG ≈ 4 - 40 kJ/mol
Salt bridge
Strengths of Noncovalent Interactions - Answer- H-bonding + Electrostatics
e.g. carboxylate (R-COO-) i protonated amine (R-NH3+)
ΔG ≈ 40 - 400 kJ/mol
Hydrophobic interactions
Strengths of Noncovalent Interactions - Answer- Displacement of water is driven by
favorable entropy
ΔG ≈ 0.4 - 4 kJ/mol
Pi stacking
Strengths of Noncovalent Interactions - Answer- Stacking of aromatic rings
greater e- delocalization
ΔG ≈ 0.4 - 4 kJ/mol
van der Waals interactions
Strengths of Noncovalent Interactions - Answer- Very weak forces between oscillating
dipoles.
,ΔG ≈ 0.4 - 4 kJ/mol
Hydrogen Bonds
are found throughout Nature - Answer- between peptide groups in polypeptides
between complementary bases of DNA (T+A)
the properties
of the universal solvent
improve solubility
Essential for biospecific recognition.
Easy to make & break (allows fast kinetics)
what are "NOT true bonds" - Answer- No overlapping of atomic or molecular orbitals
The Gibbs Equation - Answer- (ΔG = ΔH - TΔS)
Contrary to intuition, water binds tightly to apolar groups, such
that ΔHwater-binding << 0 (conversely: ΔHwater-release >> 0).
Hydrophobic interaction results in release of water molecules
increases randomness: ΔSwater-release >> 0.
Hydrophobic Interactions - Answer- The Gibbs Equation (ΔG = ΔH - TΔS) is guiding
Strictly speaking, these stabilizing interactions are NOT true bonds
Temperature strongly influences ΔG
Temperature strongly influences ΔG under Hydrophobic Interactions - Answer- At low T
(5-10oC), ΔG = ΔH - TΔS > 0: Unfavorable interaction
At higher T (37oC), ΔG = ΔH - TΔS < 0: Favorable interaction
Hydrophobic groups facilitate protein folding - Answer- protein folding
water release
Side-chains participating in hydrophobic interactions can swivel with ease, thereby
facilitating protein folding.
no orbital overlap occurs in Hydrophobic interactions. strength of int. is unaffected by
geometric considerations
, equally stable interactions
The great variety of hydrophobic side-chains maximizes packing within protein, thereby
maximizing release of bound water.(Ala,Val,Leu,Ile,Try,Tyr)
Hydrophobic interactions stabilize proteins - Answer- Strength of hydrophobic
interaction is determined by the
number of water molecules released per interaction.
Hydrophobic interactions also play dominant role in stabilizing membrane bilayer
structure.
For integral membrane proteins, hydrophobic groups are on the surface and interact
with apolar lipid side-chains of the inner membrane bilayer.
"Water Accessible Area"
"Water Accessible Area" - Answer- is a measure of the number of water molecules
needed to cover a particular hydrophobic side-chain
Behavior of Amphipathic Compounds in Aqueous Solution - Answer- flickering clusters
of H2O molecules in bulk phase
high ordered H2O molecules form cages around Hydrophobic alkyl chains
Amphipathic
molecule
Long-chain fatty acids
Long-chain fatty acids - Answer- have very hydrophobic alkyl chains, each of which is
surrounded by a layer of highly ordered water molecules.
Amphipathic
molecule - Answer- hydrophilic region
(water-like, polar or charged)
hydrophobic region (apolar)
Amphipathic Molecules in Water - Answer- - By clustering together in micelles, the fatty
acid molecules reduce the hydrophobic surface area exposed to water
