BIOL 200 - Unit 2 Questions and All
Correct Answers 2025-2026 Updated.
Discuss the structural and functional features of biological membranes and relate how the
different macromolecular components (lipids, proteins, carbs) interact to form biological
membranes - Answer
Describe the chemical properties of phospholipids, cholesterol, and glycolipids, and know how
these properties contribute to the lipid bilayer structure and function - Answer
Recognize the 30 amino acids according to their chemical properties, and their 3-letter and 1-
letter abbreviations (see textbook) - Answer
Differentiate between the primary, secondary, tertiary and quaternary levels of protein
structure - Answer
List and discuss the role of non-covalent bonds in protein folding and stabilization of protein
structure - Answer
Illustrate how the primary sequence and the environment of a protein influence its final 3D
structure - Answer
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
,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:
,- 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.
, 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
Correct Answers 2025-2026 Updated.
Discuss the structural and functional features of biological membranes and relate how the
different macromolecular components (lipids, proteins, carbs) interact to form biological
membranes - Answer
Describe the chemical properties of phospholipids, cholesterol, and glycolipids, and know how
these properties contribute to the lipid bilayer structure and function - Answer
Recognize the 30 amino acids according to their chemical properties, and their 3-letter and 1-
letter abbreviations (see textbook) - Answer
Differentiate between the primary, secondary, tertiary and quaternary levels of protein
structure - Answer
List and discuss the role of non-covalent bonds in protein folding and stabilization of protein
structure - Answer
Illustrate how the primary sequence and the environment of a protein influence its final 3D
structure - Answer
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
,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:
,- 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.
, 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
