BIOL 4100 EXAM 3 QUESTIONS AND ANSWERS WITH COMPLETE
SOLUTIONS VERIFIED LATEST UPDATE
Cell membranes are _________ barriers
selective
What is the purpose of receptors for the cell?
enable the cell to receive and process information
What is the purpose of channels and transporters for the cell?
they move stuff in and out
What is the purpose of adhesions and cytoskeleton for the cell?
they promote movement
Membrane alone allows ___________ permeability
selective
Membrane lipids are ________
phospholipids
Membrane lipids are amphipathic, which means what?
having both hydrophobic and hydrophilic parts
Membrane lipids form _________ in water
bilayers
The lipid bilayer is a flexible, ____________ fluid
two-dimensional
Movements of phospholipids within the monolayer does what to the surface?
makes a dynamic surface that 'flows'
What is the purpose of the 2-D fluid of the lipid bilayer?
,-Movements of phospholipids within the monolayer makes a dynamic surface that 'flows'
-Contributes to rapid diffusion of proteins in the membrane
-Ensures membrane molecules are distributed evenly
-Allows for fusion of membranes
When the transport vesicle shown below fuses with the plasma membrane, which
monolayer will face the cell cytosol?
Picture: circle with blue on inside, orange on outside; cytosol is on the outside
The orange monolayer will face the cytosol.
Animals exploit the phospholipid asymmetry of their plasma membrane to
distinguish between live cells and dead ones. When animal cells undergo a form
of programmed cell death called apoptosis, phosphatidylserine—a phospholipid
that is normally confined to the cytosolic monolayer of the plasma membrane—
rapidly translocates to the extracellular, outer monolayer. The presence of
phosphatidylserine on the cell surface serves as a signal that helps direct the
rapid removal of the dead cell.
How might a cell actively engineer this phospholipid redistribution?
by activating a scramblase and inactivating a flippase in the plasma membrane
Shown is a schematic diagram of a membrane phospholipid. Which segment will
always carry a negative charge?
Picture: shows phospholipid; includes tail with three portions above it (A, B, C)
,B (Phosphate)
Which membrane would show a more rapid recovery of fluorescence in a FRAP
study?
A. a membrane containing a large amount of cholesterol
B. a membrane containing a larger proportion of saturated fatty acids
C. a membrane containing equal amounts of saturated and unsaturated fatty
acids
D. The saturation of fatty acids in a cell membrane does not affect the speed of
fluorescence recovery in a FRAP study.
E. a membrane containing a larger proportion of unsaturated fatty acids
a membrane containing a larger proportion of unsaturated fatty acids
Why must all living cells carefully regulate the fluidity of their membranes?
-to allow membranes, under appropriate conditions, to fuse with one another and mix
their molecules
-to ensure that membrane molecules are distributed evenly between daughter cells
when a cell divides
-to permit membrane lipids and proteins to diffuse from their site of synthesis to other
regions of the cell
In 1925, scientists exploring how lipids are arranged within cell membranes
performed a key experiment using red blood cells. Using benzene, they extracted
the lipids from a purified sample of red blood cells. Because these cells have no
nucleus and no internal membranes, any lipids they obtained were guaranteed to
, come from the plasma membrane alone.
The extracted lipids were floated on the surface of a trough filled with water,
where they formed a thin film. Using a movable barrier, the researchers then
pushed the lipids together until the lipids formed a continuous sheet only one
molecule thick.
The researchers then made an observation that led them to conclude that the
plasma membrane is a lipid bilayer.
Which of the following would have allowed the scientists to come to this
conclusion?
The extracted lipids covered twice the surface area of the intact red blood cells.
In an electron transport chain, electrons are passed from one transmembrane
electron carrier to another, driving proton movement across a membrane (see
image below). The protons then flow through ATP synthase (not shown) to
generate ATP.
In a 2018 article (Budin, et al., Science vol. 362) researchers probed how
membrane fluidity affects electron transport chain activity and ATP production in
E. coli by manipulating membrane fluidity and measuring respiration. How could
researchers have increased membrane fluidity?
increase the proportion of phospholipids with unsaturated fatty acids
SOLUTIONS VERIFIED LATEST UPDATE
Cell membranes are _________ barriers
selective
What is the purpose of receptors for the cell?
enable the cell to receive and process information
What is the purpose of channels and transporters for the cell?
they move stuff in and out
What is the purpose of adhesions and cytoskeleton for the cell?
they promote movement
Membrane alone allows ___________ permeability
selective
Membrane lipids are ________
phospholipids
Membrane lipids are amphipathic, which means what?
having both hydrophobic and hydrophilic parts
Membrane lipids form _________ in water
bilayers
The lipid bilayer is a flexible, ____________ fluid
two-dimensional
Movements of phospholipids within the monolayer does what to the surface?
makes a dynamic surface that 'flows'
What is the purpose of the 2-D fluid of the lipid bilayer?
,-Movements of phospholipids within the monolayer makes a dynamic surface that 'flows'
-Contributes to rapid diffusion of proteins in the membrane
-Ensures membrane molecules are distributed evenly
-Allows for fusion of membranes
When the transport vesicle shown below fuses with the plasma membrane, which
monolayer will face the cell cytosol?
Picture: circle with blue on inside, orange on outside; cytosol is on the outside
The orange monolayer will face the cytosol.
Animals exploit the phospholipid asymmetry of their plasma membrane to
distinguish between live cells and dead ones. When animal cells undergo a form
of programmed cell death called apoptosis, phosphatidylserine—a phospholipid
that is normally confined to the cytosolic monolayer of the plasma membrane—
rapidly translocates to the extracellular, outer monolayer. The presence of
phosphatidylserine on the cell surface serves as a signal that helps direct the
rapid removal of the dead cell.
How might a cell actively engineer this phospholipid redistribution?
by activating a scramblase and inactivating a flippase in the plasma membrane
Shown is a schematic diagram of a membrane phospholipid. Which segment will
always carry a negative charge?
Picture: shows phospholipid; includes tail with three portions above it (A, B, C)
,B (Phosphate)
Which membrane would show a more rapid recovery of fluorescence in a FRAP
study?
A. a membrane containing a large amount of cholesterol
B. a membrane containing a larger proportion of saturated fatty acids
C. a membrane containing equal amounts of saturated and unsaturated fatty
acids
D. The saturation of fatty acids in a cell membrane does not affect the speed of
fluorescence recovery in a FRAP study.
E. a membrane containing a larger proportion of unsaturated fatty acids
a membrane containing a larger proportion of unsaturated fatty acids
Why must all living cells carefully regulate the fluidity of their membranes?
-to allow membranes, under appropriate conditions, to fuse with one another and mix
their molecules
-to ensure that membrane molecules are distributed evenly between daughter cells
when a cell divides
-to permit membrane lipids and proteins to diffuse from their site of synthesis to other
regions of the cell
In 1925, scientists exploring how lipids are arranged within cell membranes
performed a key experiment using red blood cells. Using benzene, they extracted
the lipids from a purified sample of red blood cells. Because these cells have no
nucleus and no internal membranes, any lipids they obtained were guaranteed to
, come from the plasma membrane alone.
The extracted lipids were floated on the surface of a trough filled with water,
where they formed a thin film. Using a movable barrier, the researchers then
pushed the lipids together until the lipids formed a continuous sheet only one
molecule thick.
The researchers then made an observation that led them to conclude that the
plasma membrane is a lipid bilayer.
Which of the following would have allowed the scientists to come to this
conclusion?
The extracted lipids covered twice the surface area of the intact red blood cells.
In an electron transport chain, electrons are passed from one transmembrane
electron carrier to another, driving proton movement across a membrane (see
image below). The protons then flow through ATP synthase (not shown) to
generate ATP.
In a 2018 article (Budin, et al., Science vol. 362) researchers probed how
membrane fluidity affects electron transport chain activity and ATP production in
E. coli by manipulating membrane fluidity and measuring respiration. How could
researchers have increased membrane fluidity?
increase the proportion of phospholipids with unsaturated fatty acids
