BIOL2200 midterm revision Questions With
Complete Solutions
*True or false:*
Different membranes (e.g. plasma, mitrochrondria,
ER) vary in lipid composition Correct Answers
TRUE
Contrast the results from protein versus lipid FRAP
experiments Correct Answers Reveals proteins
cannot move as freely (some may be fixed to other
structures)
Define a biological membrane Correct Answers
They define external boundaries of
cells/intracellular compartments (eukaryotic cells) -
regulating the "traffic" across the boundary.
Describe a macromolecular complex Correct
Answers Multiple different protein subunits (in
quaternary state)
Describe anterograde golgi transport Correct
Answers 1. COPII pinches vesicle from ER
2. COPII disassembles from vesicle
3. Vesicle fuses with cis-golgi network
Describe membrane proteins Correct Answers
Proteins located in or on membrane bilayer. They
have different lipid:protein ratios e.g. more
,proteins than lipids are found in bacteria,
mitrochrondria, and chloroplasts
Describe passive transport Correct Answers
Simple diffusion across permeable membrane (no
ATP required). Net flow will end once equilibrium is
reached.
Describe retrograde golgi transport Correct
Answers 1. KDEL sequence (targeting signal) is
recognised by membrane receptor in golgi
2. The protein is packaged into the retrograde
vesicle
3. The protein is released back into the ER
Describe the 2 main forms of lipid aggregates.
Provide examples Correct Answers 1. Close on
itself where the hydrophobic tails are pointed
towards the centre e.g. Micelles
2. Bilayer e.g phospholipid bilayer
Describe the 2 morphologies of mitochondria and
why they can transition from one to another
Correct Answers Morphology depends on cell
state, organism, and response to stimuli. It is
coupled with energy demand in the cell as the
mitochondria can benefit from the energy
generation. It is a dynamic process that is
controlled by the balance of mitochondrial fission +
fusion
,1. Individual spheroid/ovoids *(excess fission)*
2. Elongated networks *(excess fusion)*
Describe the 3 types of membrane proteins. What
is one main difference between them? Correct
Answers 1. Integral (transmembrane/intrinsic)
- firmly associated with the membrane (requires
detergents to release)
- Spans the whole membrane (membrane spanning
domain = hydrophobic interactions;
extramembrane domains = hydrophilic surfaces
2. Lipid-anchored
- Protein covalently linked to one or more lipid
molecules
- Lipid is embedded in one membrane leaflet to
anchor the protein
- The polypeptide does not enter the bilayer
3. Peripheral (extrinsic)
- Can be released with milder treatment (e.g.
carbonate at high pH)
- Does not contact the hydrophobic core of the
bilayer
- Forms hydrophilic interactions with membrane
surface or other membrane proteins
Main difference: strength of attachment to
membrane where integral is the strongest and
peripheral is the weakest.
, Describe the fluid-mosaic model Correct Answers
Lipids are in constant motion and therefore the
phospholipid bilayer acts more like a fluid than
solid.
- Lipids and proteins within the membrane can
diffuse laterally
- Almost no unassisted flipping
Describe the insertion of type I proteins Correct
Answers *stop-transfer anchor* (same as secreted
proteins + membrane embedding step) - works in
same topology as protein synthesis
Before the protein makes its way through the ER
lumen, there is a stop-transfer anchor:
1. Stop transferring
2. Anchor into membrane
3. Diffuse laterally out of pore
4. Ribosome completes translation with C-terminus
sticking out on cytoplasmic side
Describe the insertion of type II proteins Correct
Answers *Type 2 = 2 jobs at the same time*
*Signal-anchor sequence*
1. First part of protein is translated until the signal-
anchor sequence is reached (in middle of protein)
2. Cell flanks signal-anchor sequence with
positively charged amino acids = electrostatic
repulsion away from lipid bilayer
Complete Solutions
*True or false:*
Different membranes (e.g. plasma, mitrochrondria,
ER) vary in lipid composition Correct Answers
TRUE
Contrast the results from protein versus lipid FRAP
experiments Correct Answers Reveals proteins
cannot move as freely (some may be fixed to other
structures)
Define a biological membrane Correct Answers
They define external boundaries of
cells/intracellular compartments (eukaryotic cells) -
regulating the "traffic" across the boundary.
Describe a macromolecular complex Correct
Answers Multiple different protein subunits (in
quaternary state)
Describe anterograde golgi transport Correct
Answers 1. COPII pinches vesicle from ER
2. COPII disassembles from vesicle
3. Vesicle fuses with cis-golgi network
Describe membrane proteins Correct Answers
Proteins located in or on membrane bilayer. They
have different lipid:protein ratios e.g. more
,proteins than lipids are found in bacteria,
mitrochrondria, and chloroplasts
Describe passive transport Correct Answers
Simple diffusion across permeable membrane (no
ATP required). Net flow will end once equilibrium is
reached.
Describe retrograde golgi transport Correct
Answers 1. KDEL sequence (targeting signal) is
recognised by membrane receptor in golgi
2. The protein is packaged into the retrograde
vesicle
3. The protein is released back into the ER
Describe the 2 main forms of lipid aggregates.
Provide examples Correct Answers 1. Close on
itself where the hydrophobic tails are pointed
towards the centre e.g. Micelles
2. Bilayer e.g phospholipid bilayer
Describe the 2 morphologies of mitochondria and
why they can transition from one to another
Correct Answers Morphology depends on cell
state, organism, and response to stimuli. It is
coupled with energy demand in the cell as the
mitochondria can benefit from the energy
generation. It is a dynamic process that is
controlled by the balance of mitochondrial fission +
fusion
,1. Individual spheroid/ovoids *(excess fission)*
2. Elongated networks *(excess fusion)*
Describe the 3 types of membrane proteins. What
is one main difference between them? Correct
Answers 1. Integral (transmembrane/intrinsic)
- firmly associated with the membrane (requires
detergents to release)
- Spans the whole membrane (membrane spanning
domain = hydrophobic interactions;
extramembrane domains = hydrophilic surfaces
2. Lipid-anchored
- Protein covalently linked to one or more lipid
molecules
- Lipid is embedded in one membrane leaflet to
anchor the protein
- The polypeptide does not enter the bilayer
3. Peripheral (extrinsic)
- Can be released with milder treatment (e.g.
carbonate at high pH)
- Does not contact the hydrophobic core of the
bilayer
- Forms hydrophilic interactions with membrane
surface or other membrane proteins
Main difference: strength of attachment to
membrane where integral is the strongest and
peripheral is the weakest.
, Describe the fluid-mosaic model Correct Answers
Lipids are in constant motion and therefore the
phospholipid bilayer acts more like a fluid than
solid.
- Lipids and proteins within the membrane can
diffuse laterally
- Almost no unassisted flipping
Describe the insertion of type I proteins Correct
Answers *stop-transfer anchor* (same as secreted
proteins + membrane embedding step) - works in
same topology as protein synthesis
Before the protein makes its way through the ER
lumen, there is a stop-transfer anchor:
1. Stop transferring
2. Anchor into membrane
3. Diffuse laterally out of pore
4. Ribosome completes translation with C-terminus
sticking out on cytoplasmic side
Describe the insertion of type II proteins Correct
Answers *Type 2 = 2 jobs at the same time*
*Signal-anchor sequence*
1. First part of protein is translated until the signal-
anchor sequence is reached (in middle of protein)
2. Cell flanks signal-anchor sequence with
positively charged amino acids = electrostatic
repulsion away from lipid bilayer
