BIOL 200 - Unit 2 Exam Questions with
Correct Answers
Biological membrane similarities and differences - ANSWER-All membranes in the
cell share some common features, despite the fact that they each have a different
composition, fluidity and permeability.
Phospholipid bilayer vs Biological membranes - ANSWER-All membranes are made
of bilayers, but not all bilayers are membranes.
*Phospholipid bilayer* - made only of phospholipids and nothing else
*Lipid bilayer* - made exclusively of lipids, and nothing else
*Biological membrane*
- more complex
- will have many types of lipids in it (including glycolipids and cholesterol) as well as
proteins of various sizes, shapes and functions.
Membranes - ANSWER-- barriers that define compartments
- Separate the cell from the external environment; allows cells to maintain
concentrations of molecules inside the cell that are different than those outside
Cellular compartment - ANSWER-- A spatial domain in which molecules are free to
diffuse.
- Ex. inside vs outside of cell; inside cell cytosol vs inside intra cellular compartment
in cell (ex. mitochondria
- Biological membranes provide substantial barriers to diffusion.
Transport across the membrane - ANSWER-passive and active
- Transport across the membrane is an extremely important function that is generally
taken up by proteins. This is because membranes are highly impermeable to
biologically important compounds (like sugars and ions).
General Features of Biological Membranes - ANSWER-1. The membrane is a bilayer
made up of both lipids and proteins
2. The membrane is selectively permeable
3. The membrane is organized but fluid
4. The membrane is asymmetric
The membrane is a bilayer, made up of both lipids and proteins - ANSWER-- The
main lipid component of membranes are *phospholipids*, but they are almost never
alone in a biological membrane.
,Phospholipids are a family of molecules, but other lipids (glycolipids, sphingolipids,
cholesterol) as well as proteins will also be found in almost every biological
membrane.
- Biological membranes share the same basic structure as a phospholipid bilayer
The lipid component of membranes: formation of lipid bilayers - ANSWER-- In water,
fats and oils will come together to form large drops.
Membrane lipids are able to form sheets because of 2 characteristics:
*1. amphipathic* - one section (the 'head') can freely form H-bonds with water and
one section (the 'tails') cannot
*2. cylindrical shape* - form a roughly cylindrical shape which tends to stack together
well
- The bilayer is an elegant solution that allows sheets to form.
- It allows repair, called self-sealing. and the formation of new membrane bound
vesicles.
What do you think that the implications of the non-aqueous zone in the middle of a
phospholipid bilayer is for the transfer of molecules of different types across the
bilayer? - ANSWER-- prevents hydrophilic molecules from getting through without
the aid of a transport protein???
What do you think the permeability of lipid bilayers to water would be? - ANSWER--
Low permeability, as water is hydrophilic???
Would you expect the permeability of biological membranes to water to be higher or
lower than that of a phospholipid bimolecular leaflet? Why or why not? - ANSWER-
Less permeable, because the phospholipid bimolecular leaflet would have
amphipathic properties favouring the hydrophilic and hydrophobic regions of the
bilayer????
When can lipid bilayers form stable sheets? - ANSWER-Lipid bilayers can form
stable sheets if they are supported by other structures.
By themselves, sheets spontaneously form into spherical bodies called *liposomes*
that have water on the inside as well as on the outside. Liposomes have been used
for delivery of drugs and other agents.
In both of these cases water is excluded from the central portion of the bilayer
creating a barrier that is impermeable to water. In its simplest manifestation, a cell is
simply a glorified liposome!
Why are membranes not built from fatty acids? Why do they form micelles? What's
the difference here? - ANSWER-See panel 2-4 in text
Phospholipid bilayers are held together by hydrophobic interations - ANSWER--
Thermodynamics
- Formation of phospholipid bilayer is energetically favourable. It is energetically
more favourable for phospholipids to clump together and form a bilayer in water than
it is form them to remain dispersed.
, If a hole is punched in a lipid bilayer or a biological membrane, it rapidly seals up
(which is also why bilayers spontaneously form spheres). The latter phenomenon is
the result of the energetically favourable formation of a completely hydrophobic zone
within the bilayer and the fluidity of the molecules within the layers.
Lipid bilayers are stable because - ANSWER-association of hydrophobic groups
results in less disruption of the hydrogen bonded structure of the surrounding *water
molecules*
- The overall free energy is reduce because of the entropy of the system
-Increase in the entropy of the water molecules which is energetically favourable
2 critical points:
1. Hydrophobic groups force the surrounding water molecules into an energetically
unfavourable configuration that distorts the normal hydrogen bonded structure of
water.
2. If we have a system with a whole bunch of separated hydrophobic groups and
consider what happens if the hydrophobic groups are brought together into a cluster,
there is a significant decrease in the area of the shell of water with distorted
hydrogen bonding structure around the composite of all of the hydrophobic groups
as compared to the total associated with all of them in an individual, ungrouped
state. This net reduction of the number of 'constrained' water molecules provides an
increase in entropy that provides the free energy change responsible for the
stabilization of hydrophobic structures in aqueous systems.
The free energy equation - ANSWER-∆G = ∆H - T∆S
∆G: Gibb's free energy change
∆H: change in enthalpy
∆S: change in entropy
T: temperature
** Rxns are energetically favourable when ∆G is *negative*
Proteins - ANSWER-- An understanding of protein structure is essential in order to
understand cell biology.
1. Proteins = long chains of amino acids that are covalently bonded together via
peptide bonds
- Proteins are bonded together based on the sequence of codons that were read
from the mRNA by the ribosome.
- There are 20 diff aa used to form proteins (Translation)
- The long chain of aa is also called the primary structure/sequence.
2. Proteins fold in a very specific way depending on the order of the amino acids in
their primary sequence
- They will spontaneously fold into the shape that is most stable and requires the
least amount of energy to maintain
- Mutations often result in an increase of improper folding due to the changes in the
properties of the aa side chains in the primary sequence
Correct Answers
Biological membrane similarities and differences - ANSWER-All membranes in the
cell share some common features, despite the fact that they each have a different
composition, fluidity and permeability.
Phospholipid bilayer vs Biological membranes - ANSWER-All membranes are made
of bilayers, but not all bilayers are membranes.
*Phospholipid bilayer* - made only of phospholipids and nothing else
*Lipid bilayer* - made exclusively of lipids, and nothing else
*Biological membrane*
- more complex
- will have many types of lipids in it (including glycolipids and cholesterol) as well as
proteins of various sizes, shapes and functions.
Membranes - ANSWER-- barriers that define compartments
- Separate the cell from the external environment; allows cells to maintain
concentrations of molecules inside the cell that are different than those outside
Cellular compartment - ANSWER-- A spatial domain in which molecules are free to
diffuse.
- Ex. inside vs outside of cell; inside cell cytosol vs inside intra cellular compartment
in cell (ex. mitochondria
- Biological membranes provide substantial barriers to diffusion.
Transport across the membrane - ANSWER-passive and active
- Transport across the membrane is an extremely important function that is generally
taken up by proteins. This is because membranes are highly impermeable to
biologically important compounds (like sugars and ions).
General Features of Biological Membranes - ANSWER-1. The membrane is a bilayer
made up of both lipids and proteins
2. The membrane is selectively permeable
3. The membrane is organized but fluid
4. The membrane is asymmetric
The membrane is a bilayer, made up of both lipids and proteins - ANSWER-- The
main lipid component of membranes are *phospholipids*, but they are almost never
alone in a biological membrane.
,Phospholipids are a family of molecules, but other lipids (glycolipids, sphingolipids,
cholesterol) as well as proteins will also be found in almost every biological
membrane.
- Biological membranes share the same basic structure as a phospholipid bilayer
The lipid component of membranes: formation of lipid bilayers - ANSWER-- In water,
fats and oils will come together to form large drops.
Membrane lipids are able to form sheets because of 2 characteristics:
*1. amphipathic* - one section (the 'head') can freely form H-bonds with water and
one section (the 'tails') cannot
*2. cylindrical shape* - form a roughly cylindrical shape which tends to stack together
well
- The bilayer is an elegant solution that allows sheets to form.
- It allows repair, called self-sealing. and the formation of new membrane bound
vesicles.
What do you think that the implications of the non-aqueous zone in the middle of a
phospholipid bilayer is for the transfer of molecules of different types across the
bilayer? - ANSWER-- prevents hydrophilic molecules from getting through without
the aid of a transport protein???
What do you think the permeability of lipid bilayers to water would be? - ANSWER--
Low permeability, as water is hydrophilic???
Would you expect the permeability of biological membranes to water to be higher or
lower than that of a phospholipid bimolecular leaflet? Why or why not? - ANSWER-
Less permeable, because the phospholipid bimolecular leaflet would have
amphipathic properties favouring the hydrophilic and hydrophobic regions of the
bilayer????
When can lipid bilayers form stable sheets? - ANSWER-Lipid bilayers can form
stable sheets if they are supported by other structures.
By themselves, sheets spontaneously form into spherical bodies called *liposomes*
that have water on the inside as well as on the outside. Liposomes have been used
for delivery of drugs and other agents.
In both of these cases water is excluded from the central portion of the bilayer
creating a barrier that is impermeable to water. In its simplest manifestation, a cell is
simply a glorified liposome!
Why are membranes not built from fatty acids? Why do they form micelles? What's
the difference here? - ANSWER-See panel 2-4 in text
Phospholipid bilayers are held together by hydrophobic interations - ANSWER--
Thermodynamics
- Formation of phospholipid bilayer is energetically favourable. It is energetically
more favourable for phospholipids to clump together and form a bilayer in water than
it is form them to remain dispersed.
, If a hole is punched in a lipid bilayer or a biological membrane, it rapidly seals up
(which is also why bilayers spontaneously form spheres). The latter phenomenon is
the result of the energetically favourable formation of a completely hydrophobic zone
within the bilayer and the fluidity of the molecules within the layers.
Lipid bilayers are stable because - ANSWER-association of hydrophobic groups
results in less disruption of the hydrogen bonded structure of the surrounding *water
molecules*
- The overall free energy is reduce because of the entropy of the system
-Increase in the entropy of the water molecules which is energetically favourable
2 critical points:
1. Hydrophobic groups force the surrounding water molecules into an energetically
unfavourable configuration that distorts the normal hydrogen bonded structure of
water.
2. If we have a system with a whole bunch of separated hydrophobic groups and
consider what happens if the hydrophobic groups are brought together into a cluster,
there is a significant decrease in the area of the shell of water with distorted
hydrogen bonding structure around the composite of all of the hydrophobic groups
as compared to the total associated with all of them in an individual, ungrouped
state. This net reduction of the number of 'constrained' water molecules provides an
increase in entropy that provides the free energy change responsible for the
stabilization of hydrophobic structures in aqueous systems.
The free energy equation - ANSWER-∆G = ∆H - T∆S
∆G: Gibb's free energy change
∆H: change in enthalpy
∆S: change in entropy
T: temperature
** Rxns are energetically favourable when ∆G is *negative*
Proteins - ANSWER-- An understanding of protein structure is essential in order to
understand cell biology.
1. Proteins = long chains of amino acids that are covalently bonded together via
peptide bonds
- Proteins are bonded together based on the sequence of codons that were read
from the mRNA by the ribosome.
- There are 20 diff aa used to form proteins (Translation)
- The long chain of aa is also called the primary structure/sequence.
2. Proteins fold in a very specific way depending on the order of the amino acids in
their primary sequence
- They will spontaneously fold into the shape that is most stable and requires the
least amount of energy to maintain
- Mutations often result in an increase of improper folding due to the changes in the
properties of the aa side chains in the primary sequence
