Download Membranes - OnCourse

Ms. Hughes
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All living things respond to their
environments.
Homeostasis is the maintenance of stable
internal conditions in a changing
environment.
One way that a cell maintains homeostasis is
by controlling the movement of substances
across the cell membrane.
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Every cell is surrounded by a cell membrane.
The cell membrane protects the cell and
helps move substances and messages in and
out of the cell.
By regulating transport the cell membrane
helps the cell maintain homeostasis.
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Cells are suspended in a fluid environment.
Even cell membranes are fluid.
They are a sea of lipids in which proteins
float.
They also provide structural support for the
cytoplasm, recognizes foreign material and
communicates with other cells.
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The cell membrane is made up of a
phospholipid bilayer, which consists of a
phosphate (hydrophilic/polar) head and a two
fatty acid (hydrophobic/nonpolar) tails.
These phospholipids form a double
membrane in which both heads are facing out
of the cell.
The phospholipids forma barrier through
which only small nonpolar substances can
pass.
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Some proteins found within the membrane
face out, some face in the membrane, and
some stretch across the entire membrane.
Proteins are made of amino acids (some a.a.
are polar and others are nonpolar).
Polar proteins are attracted to the outside
water of the membrane while nonpolar
proteins are forced inside the membrane.
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Cell surface markers
Receptor proteins
Enzymes
Transport proteins
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Similar to a name tag
A chain of sugar identifies each type of cell
These sugars are attached to the cell surface
by proteins called glycoproteins.
Glycoproteins help cells work together.
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Enable a cell to sense its surroundings
They bind to certain substances outside the
cell.
Once they are bound to the substances
outside the cell changes within the cell take
place.
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Proteins with in the cell membrane that help
with important biochemical reactions inside
the cell.
These can be to increase the speed of a
reaction or decrease the speed of a reaction.
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Many substances the cell needs cannot pass
through the lipid bilayer in between the two
phosphate heads.
Transport proteins aid the movement of
substances that cannot typically pass into and
out of the cell through the cell membrane.
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Draw label and throughly explain the
phospholipid bilayer.
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The cell must move substances of varying
size, electrical charge, and composition into
and out of the cell.
In active transport across the membrane the
cell uses energy.
In passive transport across the membrane the
cell does not use energy.
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Equilibrium: when a space is filled evenly.
Concentration: the amount of a particular
substance in a given volume.
Concentration gradient: when one area has a
higher concentration than another.
Substances move from an area of high
concentration to an area of low
concentration.
Some substance enter and exit the cell by
diffusing across the cell membrane.
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Diffusion: movement from high concentration
to low concentration (movement down the
concentration gradient).
In passive transport substances enter the cell
by diffusing across the cell membrane. ( This
does not require energy)
Direction of diffusion depends on direction of
the concentration gradient.
Diffusion can be through transport proteins
and some is across the lipid bilayer.
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Food coloring example of simple diffusion.
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Small nonpolar molecules can pass directly
through the lipid bilayer. (Simple diffusion)
Molecules must move down the concentration
gradient.
Molecules which diffuse simply are nonpolar
and fat soluble.
Diffusion can take place in both directions
but with different molecules.
◦ Ex: oxygen diffuses in as carbon dioxide diffuses
out of the cell.
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During facilitated diffusion transport proteins
help substances diffuse through the cell
membrane.
Two types of facilitated transport proteins:
◦ Channel proteins
◦ Carrier proteins
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Ions, sugars, and amino acids can diffuse
through the cell membrane through channel
proteins.
These proteins aka pores serve as tunnels
through the lipid bilayer.
Each tunnel allows for a specific substance to
diffuse through it. This substance has a
specific size and charge.
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Transport substances that fit within their
binding site.
A carrier protein binds to a specific substance
on a specific side of the cell membrane.
This binding causes the substance to change
shape.
As the shape changes the protein is moved
across the membrane and release on the
other side.
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Diffusion across a selectively permeable
membrane.
Osmosis allows cells to maintain water
balance as their environment changes.
Osmosis allows for water molecules to move
down the concentration gradient to create an
equilibrium between the cell and the external
environment.
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Polar water molecules do not diffuse directly
across the bilayer.
The cell membrane contains channel proteins
that only water can pass through.
Osmosis in cells is a type of facilitated
diffusion.
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Hypotonic – the fluid outside the cell is less
concentrated. Water moves into the cell the
cell swells.
Hypertonic – the fluid outside the cell is more
concentrated. Water moves out of the cell,
the cell shrinks.
Isotonic- water moves into and out of the cell
at the same rate. The cell stays the same size.
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If left unchecked a hypotonic solution could
cause a cell to burst.
Cell walls cause the cell from over swelling in
plants and fungi.
Many plants are healthiest in hypotonic
environments.
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Transportation against a concentration
gradient.
Active transport requires energy to move
substances against their concentration
gradients.
Most often this energy is supplied directly or
indirectly by ATP.
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Many active transport processes use carrier
proteins to move substances.
In active transport the carrier proteins require
energy to “pump” proteins against their
concentration gradient.
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Sodium ions inside the cell bind to the carrier
protein.
ATP is transfers energy to the protein.
The protein changes shape and releases the
sodium ions outside the cell membrane.
Outside the cell potassium ions bind to the
pump.
The pump returns to its original shape and
releases the potassium ions inside the cell
membrane.
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This pump prevents sodium ions from
building up in the cell.
Osmosis results when sodium levels are high
The concentration gradients of sodium and
potassium ions also help transport other
substances, such as glucose across the cell
membrane.
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McGraw – Hill video of sodium potassium
pump
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Many proteins and polysaccharides are too
large to enter the cell using carrier proteins,
so they use vesicles.
Vesicles are membrane bound sacs.
The vesicle membrane is a lipid bilayer, so
vesicles can bud off from the membrane, fuse
with it or fuse with other vesicles.
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Endocytosis: movement of a large substance
into the cell by means of a vesicle.
During endocytosis the membrane forms a
pouch around the substance, pinches off and
forms a vesicle inside the cell.
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Exocytosis: movement of material out of a
cell by means of a vesicle.
During exocytosis a vesicles inside the cell
fuse with the cell membrane. The contents of
the vesicle are then release outside of the cell
through the cell membrane.
Exocytosis is used to transport proteins
modified by the Golgi apparatus.
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McGraw Hill video of endo and exo cytosis.
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We will now go outside and form the
phospholipid bilayer and allow molecules to
either diffuse through us or we will actively
pump large molecules through.
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Create a story book of a molecules who are
being transported. These molecules must
experience active and passive transport.
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Cells communicate and coordinate activity by
sending chemical signals that carry
information to other cells.
Signaling cell – produces signal.
Target cell – receives signal intended for it.
Signal – molecule detected by target cell.
Typically target cells have specific proteins
that recognize and respond to the signal.
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Cells can communicate through direct contact
between their membranes.
Short-distance signals may act locally.
Long-distance signals are carried by
hormones and nerve cells.
Hormones are made in one part of the body
and distributed by the bloodstream but effect
only specific cells.
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Most signal molecules originate within the
body, some signals come from outside.
Ex: light has a great effect on the action of
hormones in plants. Length of day
determines when some plants flower.
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A target cell is bombarded by hundreds of
signals.
It recognizes and responds to only a few
specific signals
Signal: anything that serves to direct, guide,
or warn.
Receptor protein: a protein that binds specific
signal molecules, which causes the cell to
respond.
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A receptor protein binds only to signals that
match the specific shape of its binding site.
Only signals that have the specific shape can
bind to the specific receptor, others have no
effect.
Once bound the signal molecule the receptor
protein changes its shape in the membrane.
This change relays information to the
cytoplasm of the target cell. (communication)
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Permeability change: transport proteins may
open or close due to a signal.
Enzyme activation: Enzymes may be activated
by a signal or some proteins may be enzymes
themselves.
Second messenger: a second message may be
formed and sent. Ex: to the nucleus of the
target cell.
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Create flow chart of steps for cell
communication.
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Using index cards or paper:
◦ Write down the steps for cell communication and
practice placing them in order.