BIO 315 EXAM 2 STUDY GUIDE ITH
COMPLETE SOLUTIONS
1. Describe the biological role of membranes - Correct Answers -a.
Compartmentalization: enclose intracellular compartments
b. Scaffold for biochemical activities: provide a framework that organizes enzymes for
effective interaction
c. Selectively permeable barrier: regulate exchange of substances between
compartments
d. Transporting solutes
e. Responding to external signals: receptors transduce signals from extracellular ligands
f. Intracellular interaction: mediate recognition and interaction between adjacent cells,
like antibodies
g. Energy transduction: transduce photosynthetic energy, convert energy to ATP
1. Describe how membranes form spontaneously due to free energy minimization, with
a large entropic driving force - Correct Answers -a. Water likes to H-bond and constantly
move. H bonds are constantly breaking and reforming = high entropy = high disorder.
Water has to avoid the FA tails = order = low entropy (not thermodynamically favorable).
b. Thermodynamics drives membranes to form sealed compartments. Energetically
unfavored planar phospholipid bilayers with edges exposed to water. Because it is
unfavored to have the fatty acid tails interacting with the water, so the fatty acid tails
associate with each other so no fatty acid tails are exposed.
c. This is how liposomes are created, so they can deliver drugs. The membranes
spontaneously form, which traps the solvent inside which can be used as a drug
delivery device
1. Know the structure and function of membrane lipids (phosphoglycerides,
sphingolipids, cholesterol) - Correct Answers -a. Phosphoglycerides (phopsholipids):
diacylglycerides with small functional head groups linked to the glycerol backbone by
phosphate ester bonds. Can differ in polar head group, length of fatty acid chain (16-22
C's long), level of fatty acid saturation
b. Sphingolipisds: ceramides formed by the attachment of sphingosine to fatty acids.
Fatty acid chains tend to be longer and more highly saturated than phosphoglycerides.
Additional groups can be added to the terminal alcohol of the sphingosine. If a
carbohydrate is added, it forms a glycolipid
c. Cholesterol: smaller and less amphipathic lipid that is only found in animals (big role
in membrane fluidity). Steroid molecule. Plants/bacteria do not have cholesterol. Makes
membrane more fluid at low temps and more ordered at high temps. Carbon rings are
flat and rigid, therefore interfere with movement of phospholipid fatty acid tails.
Cholesterol molecules are sandwiched between fatty acid tails of phospholipids
, 1. Explain how the shape and chemical properties of lipids influence the shape and
properties of molecular assemblies they create (bilayer, micelles, etc.) - Correct
Answers -a. Lipids contorting to interact closely with membrane protein: example of why
membrane thickness varies
1. Explain the fluid-mosaic model of plasma membrane structure and modern-day
revisions of it - Correct Answers -a. Core lipid bilayer exists in a fluid state, capable of
movement. Lipid bilayer exists primarily in 3D (external carbohydrate chains, internal
cytoskeleton). Membrane proteins form a mosaic of particles penetrating the lipids.
Heterogeneous in lipid and protein composition, formation of distinct domains
b. Fluidity implies lipids and proteins can float in the membrane via diffusion.
c. Current: mosaicism is high, fluidity/diffusion is limited for many molecules. Membrane
thickness is not uniform, proteins bind together and function in complexes, large protein
domains on either side of bilayer limit accessibility of bilayer.
1. Describe various lipid and proteins components of membranes and how these vary
across cell types, organelles, and leaflets - Correct Answers -a. Lipid: polar head
groups, glycerol backbone, fatty acid chains (tails).
b. Lipid bilayer exists primarily in two dimensions. Contains many membrane embedded
proteins. Heterogeneous in lipid and protein composition, formation of distinct domains
1. Describe how molecules move within membranes - Correct Answers -a. Rotate,
diffuse, but rarely flop bilayers.
1. Provide examples of the importance of the fluid-mosaic model to cellular functions -
Correct Answers -a. Barrier to transport, separates compartments, provides framework
so biochemical activities are organized, responds to signals with receptors on the
membrane, transduces energy
1. Identify the types of membrane proteins (integral, peripheral, lipid anchored) - Correct
Answers -a. Integral proteins: penetrate into and may pass through lipid bilayer; make
up 20-30% of all encoded proteins. Amphipathic; 20-30 nonpolar AA forming
hydrophobic interactions with FA tails of PL, polar AA, hydrophilic regions forming
functional domains outside the bilayer. Channel proteins have hydrophilic cores that
form aqueous channels in the membrane-spanning region. Nonionic detergents are
used to solubilize IMPs, disrupts membrane and allows protein isolation.
b. Peripheral proteins: located entirely outside of bilayer on either side of extracellular or
cytoplasmic side. Associated with the membrane surface by weak electrostatic
interactions (noncovalent bonds) and are easily solubilized. Can be associated with PL
head group (hydrophilic interaction), hydrophobic core (stretch of hydrophobic AA),
intracellular domain of IMP (protein-protein binding motif)
c. Lipid-anchored membrane proteins: distinguished both by the types of lipid anchor
and their orientation. GPI linked proteins found on outer leaflet can be released by
inositol-specific phospholipases. Some inner leaflet proteins are anchored to membrane
COMPLETE SOLUTIONS
1. Describe the biological role of membranes - Correct Answers -a.
Compartmentalization: enclose intracellular compartments
b. Scaffold for biochemical activities: provide a framework that organizes enzymes for
effective interaction
c. Selectively permeable barrier: regulate exchange of substances between
compartments
d. Transporting solutes
e. Responding to external signals: receptors transduce signals from extracellular ligands
f. Intracellular interaction: mediate recognition and interaction between adjacent cells,
like antibodies
g. Energy transduction: transduce photosynthetic energy, convert energy to ATP
1. Describe how membranes form spontaneously due to free energy minimization, with
a large entropic driving force - Correct Answers -a. Water likes to H-bond and constantly
move. H bonds are constantly breaking and reforming = high entropy = high disorder.
Water has to avoid the FA tails = order = low entropy (not thermodynamically favorable).
b. Thermodynamics drives membranes to form sealed compartments. Energetically
unfavored planar phospholipid bilayers with edges exposed to water. Because it is
unfavored to have the fatty acid tails interacting with the water, so the fatty acid tails
associate with each other so no fatty acid tails are exposed.
c. This is how liposomes are created, so they can deliver drugs. The membranes
spontaneously form, which traps the solvent inside which can be used as a drug
delivery device
1. Know the structure and function of membrane lipids (phosphoglycerides,
sphingolipids, cholesterol) - Correct Answers -a. Phosphoglycerides (phopsholipids):
diacylglycerides with small functional head groups linked to the glycerol backbone by
phosphate ester bonds. Can differ in polar head group, length of fatty acid chain (16-22
C's long), level of fatty acid saturation
b. Sphingolipisds: ceramides formed by the attachment of sphingosine to fatty acids.
Fatty acid chains tend to be longer and more highly saturated than phosphoglycerides.
Additional groups can be added to the terminal alcohol of the sphingosine. If a
carbohydrate is added, it forms a glycolipid
c. Cholesterol: smaller and less amphipathic lipid that is only found in animals (big role
in membrane fluidity). Steroid molecule. Plants/bacteria do not have cholesterol. Makes
membrane more fluid at low temps and more ordered at high temps. Carbon rings are
flat and rigid, therefore interfere with movement of phospholipid fatty acid tails.
Cholesterol molecules are sandwiched between fatty acid tails of phospholipids
, 1. Explain how the shape and chemical properties of lipids influence the shape and
properties of molecular assemblies they create (bilayer, micelles, etc.) - Correct
Answers -a. Lipids contorting to interact closely with membrane protein: example of why
membrane thickness varies
1. Explain the fluid-mosaic model of plasma membrane structure and modern-day
revisions of it - Correct Answers -a. Core lipid bilayer exists in a fluid state, capable of
movement. Lipid bilayer exists primarily in 3D (external carbohydrate chains, internal
cytoskeleton). Membrane proteins form a mosaic of particles penetrating the lipids.
Heterogeneous in lipid and protein composition, formation of distinct domains
b. Fluidity implies lipids and proteins can float in the membrane via diffusion.
c. Current: mosaicism is high, fluidity/diffusion is limited for many molecules. Membrane
thickness is not uniform, proteins bind together and function in complexes, large protein
domains on either side of bilayer limit accessibility of bilayer.
1. Describe various lipid and proteins components of membranes and how these vary
across cell types, organelles, and leaflets - Correct Answers -a. Lipid: polar head
groups, glycerol backbone, fatty acid chains (tails).
b. Lipid bilayer exists primarily in two dimensions. Contains many membrane embedded
proteins. Heterogeneous in lipid and protein composition, formation of distinct domains
1. Describe how molecules move within membranes - Correct Answers -a. Rotate,
diffuse, but rarely flop bilayers.
1. Provide examples of the importance of the fluid-mosaic model to cellular functions -
Correct Answers -a. Barrier to transport, separates compartments, provides framework
so biochemical activities are organized, responds to signals with receptors on the
membrane, transduces energy
1. Identify the types of membrane proteins (integral, peripheral, lipid anchored) - Correct
Answers -a. Integral proteins: penetrate into and may pass through lipid bilayer; make
up 20-30% of all encoded proteins. Amphipathic; 20-30 nonpolar AA forming
hydrophobic interactions with FA tails of PL, polar AA, hydrophilic regions forming
functional domains outside the bilayer. Channel proteins have hydrophilic cores that
form aqueous channels in the membrane-spanning region. Nonionic detergents are
used to solubilize IMPs, disrupts membrane and allows protein isolation.
b. Peripheral proteins: located entirely outside of bilayer on either side of extracellular or
cytoplasmic side. Associated with the membrane surface by weak electrostatic
interactions (noncovalent bonds) and are easily solubilized. Can be associated with PL
head group (hydrophilic interaction), hydrophobic core (stretch of hydrophobic AA),
intracellular domain of IMP (protein-protein binding motif)
c. Lipid-anchored membrane proteins: distinguished both by the types of lipid anchor
and their orientation. GPI linked proteins found on outer leaflet can be released by
inositol-specific phospholipases. Some inner leaflet proteins are anchored to membrane
