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Cell Membranes
What separates intracellular and extracellular
fluid in the cell membrane?
True or False: Proteins embedded in the cell
membrane create channels or pores.
Proteins can be found: a) on the outside of the
cell membrane b) in the middle of the
membrane c) on the inside of the membrane
d) all of the above
Which proteins can turn on activities in the
cell? a) on the outside of the cell membrane b)
in the middle of the membrane c) on the
inside of the membrane d) combination of
outside, middle, inside e) all of the above
What makes cell membranes semipermeable?
Phospholipids, proteins, sugars, etc. and limit
what can travel through the membrane.
True. In autoimmune disorders, these proteins
may be perceived as antigens.
d) all of the above
What are phospholipids?
They are amphipathic, meaning water loving
AND water hating
What loves water (hydrophilic)?
The phosphate head loves water (hydrophilic) and
can attach to other water loving molecules
What hates water (hydrophobic)?
The two fatty acid (FA) tails hate water so they
bind to other water hating (hydrophobic)
molecules like lipids
What substances can cross the cell
membrane?
Substances that love lipids can get to the middle
of the membrane, but water loving substances
have a hard time crossing
Hydrophobic molecules, hydrophilic molecules
such as gases. Water can also easily cross
The cell membrane separates cells from outside
environment, it controls passage of molecules
across membranes, and it provides surface for
enzyme reactions.
Proteins
What type of molecules can cross the
membrane easily?
What chemical activities does the cell
membrane organize?
What organelle is embedded in the cell
membrane?
How do the proteins in the cellmembrane also
contribute to cell functions?
The phosphate heads of phospholipids are
hydrophilic or hydrophobic?
The fatty acid tails of phospholipids are
hydrophilic or hydrophobic?
Hydrophobic interior of membrane form a
barrier to what types of molecules,
hydrophilic or hydrophobic?
What portion of a phospholipid is
c) Proteins on the inside of the cell
Phospholipids and proteins
The proteins from selective channels, serve as
carrier proteins, and serve as receptors.
Hydrophilic (likes water)
Hydrophobic (dislikes water)
Hydrophilic molecules
Phosphate heads
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Cell Membranes
hydrophilic?
What portion of a phospholipid is non-polar?
What are the two locations where proteins can
be found in a cell membrane?
On a cell membrane, what proteins can bind
to a chemical?
On a cell membrane, what proteins can create
a pore or channel?
On a cell membrane, what proteins can start a
series of enzymatic reactions in a cell?
Fatty acid tails
Proteins can be integral (throughout the
membrane) or peripheral (one side or the other).
Peripheral proteins on the surface of the cell
membrane
Integral
Peripheral proteins on the inside of the cell
membrane
What provides function to a cell membrane?
Proteins
How do the proteins move?
Laterally
What are the (2) types of “sideness” electrical
charges the membrane show?
(1) Interior – has more negative charges
(2) Exterior – has more positive charges
How are proteins defined in the cell
membrane?
Proteins are defined by how deep they are in the
membrane
What are integral proteins?
Form channels, pores, carriers
What are peripheral proteins?
Binds chemicals, starts enzymatic reaction in cells
What is a glycoprotein?
Sugars outside of the cell which attach to the
phosphate heads or to the proteins
negatively charged
If there are many glucose molecules on the
outside of the cell, what will the charge be on
the outside of the membrane?
What is a membrane potential?
Should the inside of the cell be more negative
or more positive than the outside of the cell?
If there is a glycocalyx (sugar bundle) on the
outside of the cell, what does it do to the
charge on the OUTSIDE of the cell
membrane?
What are the three types of Carbohydrates?
What are the functions of the Carbohyrates?
What is the function of cholesterol in a cell
There is a separation of charges…one side of the
membrane is more negative than the other side
More negative inside
It makes the outside more negatively charged.
Glycoproteins, proteoglycans, and glycolipids
Carbohydrates are involved in cell to cell
attachments and interactions. They also play a
role in immune reactions.
1) Increases flexibility of the cell
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Cell Membranes
membrane?
Other than proteins, what do cell membranes
contain?
Where is this located?
What purpose does the cholesterol serve?
What can get through a cell membrane?
Which molecules cross the cell membrane via
active or passive transport (which requires the
assistance of proteins in the cell membrane)?
In regards to transporting across a membrane,
lipids by themselves are what?
Can water-soluble substances transport across
an entirely lipid membrane?
Can water transport across an entirely lipid
membrane?
Can lipid-soluble substances transport across
an entirely lipid membrane?
Is the “head” of a lipid hydrophilic or
hydrophobic?
Is the fatty acid tail of a lipid hydrophilic or
hydrophobic?
Can glucose and ions transport across an
entirely lipid membrane?
In regards to transporting across a membrane,
lipids by themselves are what?
1. What type of transport is diffusion
down a concentration gradient?
2. What are 2 types of passive transport?
what type of transport occurs against a
concentration gradient?
Is ATP required for both active and passive
transport?
3. Does active transport use a pump?
What does passive transport mean?
What does active transport mean?
2) Increases stability of the cell during
temperature changes
3) Increases hydrophobicity of the cell
membrane
Cholesterol
In the middle of the membrane
Maintains a balance of flexibility, stability and
fluidity in the cell membrane
Hydrophobic molecules (water fearing), gases
like CO2, O2, small molecules like ethanol and
H2O.
Hydrophilic molecules: i.e. glucose
Substances with a charge: i.e. K+, Na+, Cl

A barrier to water-soluble substances
Allow lipid-soluble substances to cross
through a membrane
No
Yes
Yes
Hydrophilic
Hydrophobic
No


A barrier to water-soluble substances
Allow lipid-soluble substances to cross
through a membrane
Passive transport
Simple and facilitative
Active transport
No, just active transport
yes
Passive transport means no cellular energy
required, no ATP used.
Active transport means ATP is used, either
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Cell Membranes
Where do substances go in passive transport?
Where do substances go in active transport?
What type of transport mechanism is
osmosis?
Does Osmosis require ATP?
If you have more particles on one side of a
membrane than the other, and the particles
can’t move, what will move?
What type of protein in the cell membrane
only allows water to pass?
How are aquaporins made?
directly or indirectly.
Passive transport makes substances move from
high to low concentration, down their gradient.
Active transport is when at least one solute is
moved against its concentration gradient.
Passive diffusion
No
Water will move into the compartment with the
most particles.
Aquaporins
When a cell is thirsty, a certain gene turns on, and
aquaporins are made an inserted into the cell
membrane. When the cell has enough water, the
aquaporins are removed. Genetic problems can
cause the wrong amount of aquaporins to be
made, which can cause water imbalances.
What is osmosis?
Osmosis causes a new flow of water across a
semipermeable membrane. Osmosis occurs when
water molecules move from an area of pure water
toward an area that is a water/salt solution.
Does water move up or down its
Water moves down its concentration gradient.
concentration gradient?
That means it moves from its area of high
concentration (more watery solution) to its area of
low concentration (a compartment with more
particles).
What affects osmosis?
Osmosis is affected by the solute concentration
(osmotic force) and hydrostatic forces
Is simple diffusion active or passive transport
Passive
Rate of diffusion depends on what two things?
Size of the gradient, and is the solute
permeable
If the concentration gradient is steep, what
The diffusion rate is faster
happens to the rate of diffusion?
What is a pore?
A passageway in a cell membrane that is always
open
How do small molecules enter a cell?
Simple diffusion through a pore
How do large molecules enter a cell?
Through a channel
What is a channel?
A protein that creates a passageway, and has a
gate that is not always open
What are the two types of gated channels?
Ligand gated channels and voltage gated channels
What is a ligand gated channel?
Opens only when a special chemical, such as a
neurotransmitter, binds to it
What is a voltage gated channel?
Opens only when an electrical charge is applied.
When a substance enters a cell by using a pore No, they go in by simple diffusion.
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Cell Membranes
or a gated channel, is ATP used?
What type of transport is osmosis?
Simple Diffusion is also called what?
Passive transport; no ATP is used.
Non-carrier mediated transport
Is simple diffusion passive or active transport? Passive (no energy required)
What is simple diffusion?
At equilibrium, is there a net loss or gain of
fluid?
Is tendency of molecules to spread out from an
area of HIGH concentration to an area of LOW
concentration
No, there is no net gain nor loss of fluid
What makes simple diffusion passive?
It is passive because a molecule diffuses down
concentration gradient without input of cellular
energy
What does simple diffusion need?
Simple diffusion needs:
(1) Permeability
(2) Concentration gradient
(chemical/electrical)
1. Simple diffusion.
1. Lipid-soluble molecules move readily
across cell membranes in which type
of diffusion?
2. The rate at which Lipid-soluble
molecules move depends on what?
3. How do water-soluble molecules cross
cell membranes?
4. What are the two types of channels for
water-soluble molecules
5. What are the two types of gated
channels?
What do ion channels allow for?
What are two types of ion channels?
2. The lipid solubility.
3. They cross via channels or pores (made
out of proteins).
4. Gated and ungated channels
5. Chemical gates and voltage gates
(electrical)
Ion channels allow for simple diffusion
 Ungated channels
 Gated channels
Ungated channels can be determined by what? Size, Shape, Distribution of Charge, etc.
What are two types of gated channels?
Voltage
Ligand Activated
What is an example of a voltage dependent
Voltage-dependent Na+ channels
gated channel?
What is an example of a ligand used for a
A neurotransmitter such as ACh
ligand activated gated channel?
Is facilitated diffusion active or passive?
Passive; no ATP is used
What is the difference between simple and
Facilitated requires a protein to physically bind to
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Cell Membranes
facilitated diffusion?
it and move it across the cell membrane.
Therefore, it can be saturated.
What is the rate of facilitated diffusion limited the number of carriers present
by?
What is another term for facilitated diffusion? Carrier-mediated diffusion.
What is necessary for facilitated diffusion to
A protein is required to interact with the solute
occur?
and carry it.
What limits the rate of transport of molecules The number of carriers in the membrane.
being transported across a cell membrane?
Does facilitated diffusion require energy?
No ATP (energy) is used.
Can the protein carrier transport any
No, just the specific molecule it is designed for.
molecule?
If you increase the concentration gradient,
It increases
what happens to the rate of diffusion?
When does facilitated diffusion level off?
When its velocity maximum (Vmax) is reached.
That means the carriers are saturated.
What is active transport?
Active transport is the movement of a substance
against its concentration gradient. (From low to
high concentration)
What does active transport require?
Active transport requires ATP for energy.
Is active transport used when a particle wants Active transport occurs against a concentration
to diffuse down its concentration gradient, or
gradient.
when it needs to move against its
concentration gradient?
How does a substance move against its
It involves a pump, which requires ATP
concentration gradient during active
transport?
What are the two types of active transport?
primary active transport secondary active
transport.
How does primary active transport use ATP?
Directly
How does secondary active transport use
Indirectly because it uses an electrochemical
ATP? Explain
gradient. As one molecule passes through the
membrane, it helps another molecule enter against
its concentration gradient.
When sodium enters a cell, how does it leave It has to be actively pumped back out by primary
again?
active transport
What is the term for the maximum rate of
active transport?
What is the enzyme that uses 2/3 of the cell’s
energy, and what does it do?
What is another term for secondary active
transport?
What is secondary active transport?
Vmax
Sodium-potassium ATPase
After an action potential, it pumps sodium back
out of the cell while pumping potassium back in.
Co-transport
One substance uses ATP to cross the membrane
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Cell Membranes
What are the two main forms of secondary
active transport?
As amino acids use ATP to exit a cell, it
opens a gate for sodium ions to get in. Which
substance is using secondary active transport?
What is a symport?
What is antiport?
Which has net movement of water?
• Osmosis
• Simple Diffusion
• Facilitative Transport
• Primary active Transport
• Secondary active Transport
Select all that apply: This type of transport
moves solutes down the concentration
gradient.
• Osmosis
• Simple Diffusion
• Facilitative Transport
• Primary active Transport
• Secondary active Transport
Which ones have a solute moved against its
gradient?
• Osmosis
• Simple Diffusion
• Facilitative Transport
• Primary active Transport
• Secondary active Transport
Which is moved against its gradient and
ATP is directly used?
• Osmosis
• Simple Diffusion
• Facilitative Transport
• Primary active Transport
• Secondary active Transport
Along with solutes, what other gradient to
while another sneaks in without directly using
ATP, like a revolving door.
Antiport and Symport
The sodium ions
A symport is a type of secondary active transport
where a substance is transported in the same
direction as the driver ion (Na+). For example,
when Na+ enters the cell, a glucose molecule also
enters the cell.
Antiport is a type of secondary active transport
where a substance is transported in the opposite
direction as the driver ion (Na+). For example,
when Na+ enters the cell, a glucose molecule
leaves the cell.
Simple diffusion
Simple, facilitative, secondary active transport
Primary and secondary active transport
Primary active transport
Answer: The electrical gradient
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Cell Membranes
solutes diffuse down?
Why are the insides of cells more negatively
charged than the outside of a cell?
Because there are a lot of proteins inside of cells,
and most proteins are negatively charged.
What ion can leak into and out of a cell due to
its always open channel?
Why is there a higher concentration of K+
inside the cell?
K+ ions
How negative is the inside of the cell
membrane?
What is the charge on the outside of most cell
membranes?
What is the separation of charges called?
What will happen to our cells if the charges
on both sides of the cell membrane reach
equilibrium?
What creates the selective channels that allow
particular substances to cross the cell
membrance?
What are the charged ions within the body
called?
_____________ means permeability. If
conductivity of an ion increases, it means that
the permeability of that ion increased.
_____ diffuse at a faster rate when there is
less resistance.
The more ___________ there is, the less
conductivity, and less resistance will cause
more conductivity.
_________ is a fat shealth wrapped around
the axons of some neurons. If a neuron is
myelinated, the resistance is decreased
because it makes electrical charges move
faster.
If a neuron is myelinated, the ___________ is
decreased because it makes electrical charges
move faster.
Another thing that affects speed of electrical
transmission is the _________ of the
_____________.
Bigger neurons carry current _________
Because the freely moving K+ can move into the
cell freely and is subsequently attracted to the
negatively charged proteins.
At rest the inside of most cell membranes is
minus 70 mV (milivolts)
At rest, most cell membranes are +30mV.
The membrane potential
The cells will die.
Integral proteins formed by gene expression
electrolytes
CONDUCTIVITY
IONS
RESISTANCE
MYELIN
RESISTANCE
SIZE OF THE NEURON
FASTER
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Cell Membranes
(expand the freeway to add extra lanes, you
will get home faster).
The flow of charge is _____________
The separation of opposite charges is
__________
Voltage can be described as____________
Potential
Voltage difference can be described as
_________ _____________
The opposition to charge movement (friction)
is:
Allowing a charge to move (permeability) is
_______________
What are the charged things that run through
our body fluids?
Unlike simple concentration gradients, when
dealing with things that are charged …. You
must ask a third question!
1. Is the membrane permeable to it?
2. Is there a chemical gradient for it?
– Things tend to move from high
to low concentration
3. _________________________?
Sometimes, the _____________ gradient is
favors one ion to go in one direction, and the
______________ gradient favors it to go in
the other direction. The stronger pull will win.
True or false: K+ can get back in because
its channel is always open, but Na+ has to
stay out because its channel is always
closed unless something opens it.
Explain cell resting membrane potential
Explain what factors determine a membrane's
potential (how positive or negative the
membrand charge is)
What ion is most permeable to the cell
membrane?
Are cells permeable to proteins?
What is the term for when particles want to
CURRENT
VOLTAGE
POTENTIAL
POTENTIAL DIFFERENCE
RESISTANCE
CONDUCTANCE
ELECTROLYTES!
IONS: Na+, K+, Cl-, Ca++
3.Is there an electrical gradient for it?
- Things tend to move to regions of opposite
charge
Only then, can you predict if the substance will
move across the membrane!
CHEMICAL
ELECTRICAL
True
Ion concentration gradients and differences in
membrane permeability cause an overall charge
of -70 to -90 mv.
The permeability of the cell membrane to K+ or
Na+ determines the membrane's potential.
Potassium (K+)
No, they are too big
The Nernst potential
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Cell Membranes
diffuse down their concentration gradient, but
the charges they carry want to go in the
opposite direction, and the forces cancel each
other out so there is no net gain or loss?
Why can you not let sodium continue on into
the cell until it reaches equilibrium?
How do you prevent too much sodium from
entering the cell?
When there is an action potential, what gate
opens first?
Sodium rushes into the cell, changing the
voltage on the inside of the cell membrane
from negative to positive. Will the outside of
the cell be positive or negative?
What are the two reasons, K+ does not want
to stay inside the cell any more?
Sodium cannot leave a cell once it is inside,
how can it leave?
A cell at rest or during action potential will
ATPase ever stop working?
What are excitable cells?
In an excitable cell, what is the temporary
change in voltage is due to?
What is an action potential?
What is the resting potential of a cell?
Which side of a cell membrane usually has
more negative charges? What causes this?
In a cell membrane, what does “polarized”
mean?
What is depolarization?
When does depolarization happen?
What is hyperpolarization?
the cell will not be able to metabolize, and it will
die.
the Na+ channels remain closed most of the time
the sodium gate opens first and the potassium gate
opens second.
Negative
to diffuse down its concentration gradient, and to
diffuse down its electrical gradient. When it
leaves the cell, taking its positive charges with it,
the outside of the cell membrane flips from
negative back to positive again
. It has to be pumped out, by sodium-potassium
ATPase (the mother protein, or housekeeping
protein).
No, Na-K ATPase is active all the time
Cells that can experience a momentary change in
membrane voltage
a momentary change in permeability to sodium
(Na+)
When there is a reversal of charges on the inside
and the outside of the cell membrane and the cell
becomes positive inside and negative outside
When the sum of all the positive and negative
charges on the inside of the cell membrane is
about minus 70 mV
The inside. There are many proteins inside a cell,
and they have a negative charge.
A charge is present in the membrane…it is not at
zero.
When the charge on the inside of the cell
membrane becomes less negative (closer to 0
mV), so it is getting closer to starting an action
potential.
When sodium is entering the cell, bringing its
positive charges with it.
When the overall charge on the inside of the cell
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Cell Membranes
When does hyperpolarization occur?
What is repolarization?
What does the term “threshold” mean,
regarding charges in a cell membrane?
To depolarize a cell, what kind of charge must
be put into the cell, positive or negative?
When cell membranes are at their resting
membrane potential, are they also at their
resting potassium ion potential?
How does sodium enter and leave a cell?
Do action potentials vary in size, according to
the strength of the stimulus?
When an action potential continues down the
axon of a neuron, does it diminish in size?
When sodium channels are open, is ATP
used?
How does sodium leave the cell once it is
inside?
When is ATP used during an action potential?
Do larger neurons carry current faster or
slower than smaller neurons?
When resistance increases at a cell membrane,
what happens to the conductivity of ions?
What substances are in high concentration on
the inside of the cell?
What substances are in high concentration on
the outside of the cell?
What substances are in high concentration in
plasma?
What substances are in low concentration in
plasma?
membrane becomes more negative (farther away
from 0 mV, so it is farther away from starting an
action potential)
When potassium (K+) is leaving the cell but
sodium is not entering.
When the charges on the inside of the cell
membrane return to about minus 70 mV after
having been depolarized or hyperpolarized.
Threshold is the point at which the charges begin
to be positive on the inside of the cell membrane
and negative on the outside of the cell membrane.
This triggers an action potential
Positive
No
It enters by a sodium channel, which opens when
a neuron stimulates the cell. It leaves by the
Na+/K+ ATPase pump
No; they are uniform in size. Either an action
potential is triggered (at threshold) or it is not.
No, each action potential spike is the same height
as it continues down the axon. It does not
diminish in size as it gets farther from the initial
stimulus.
No; once the channels are open, Na+ enters the
cell by simple diffusion
It is pumped out, by a sodium/potassium pump.
As sodium is pumped out, K+ is pumped in.
ATP is required to pump the sodium out of the
cell, which returns the cell to its RMP
Faster
Conductivity decreases
Potassium and proteins
Sodium and calcium
Sodium and calcium
Potassium and proteins
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