Download Cell Transport

Homeostasis means maintaining a
balance internally despite what is going
on externally.
 Organisms must adjust to changes in the
environment in order to survive or they
could die!


For example, if it is below
freezing outside, you must
put on a heavy coat,
gloves, double socks, a
warm hat, ear muffs, and
lots and lots of layers to
maintain a healthy
INTERNAL body
temperature despite the
EXTERNAL temperature
What structure maintains homeostasis in
our cells?
The Cell Membrane
 How does it maintain homeostasis?

By controlling the passage of molecules,
such as water, salts, food particles, etc in
and out of the cell.
(it regulates what enters and leaves)

How? Through passive transport,
active transport and cell to cell
communication!
The Cell Membrane is:
 A phospholipid bilayer
 Two layers made of proteins and lipids
Phospholipid Structure:
 Polar Head (hydrophilic—”water loving”)
 Nonpolar Tails—(hydrophobic—”water fearing”)
Draw:

Polar Head
(hydrophillic)
Nonpolar Tails
(hydrophobic)
Bilayer arrangement
 Draw:

The proteins embedded in the cell
membrane help it to function properly
 3 Types of Membrane Proteins

›
›
›
Transport—helps molecules enter or leave the
cell
Marker—identify the cell
Receptor—allow cells to communicate
Transport Proteins
 Function as
“gates/passageway”

Allow sugars, salts, etc to
cross the membrane.

Special channel proteins:
Transport
Protein
› Gated ion channels—gates
that open/close
› Carrier proteins—change
shape to allow specific
molecule to pass
› Aquaporins-allow water to
diffuse through (called
osmosis)
Carrier
Protein
Channel
Protein
Marker Proteins
 Cell’s “Name Tag”
 Protein sticks out of phospholipid
layer
 Often has carbohydrates attached
to outside end
 Functions in cell identification to
identify the cell to other cells and
molecules
Marker Protein
 Important in
› immunity—so various white blood
cells in your body do not mistake
your cells for foreign cells
- blood typing – so you can’t
receive just any ol’ type of blood
Receptor Proteins
 Function as
“messenger/receiver”
 Receive information from
the environment
(extracellular fluid, blood,
interstitial fluid) and
transmit that info to the
inside of the cell
 Protein has specific
shape/charge to only
allow certain molecules
(like hormones) to bond
 Triggers a response in cell
http://personal.tmlp.com/Jimr57/
textbook/chapter3/cms2.htm
Receptor Protein
 Proteins
are
embedded/float
-ing in the lipid
bilayer.
The Cell Membrane is:
 Selectively permeable/semipermeable
 permeable means to let objects travel through
 so if it is selectively or semi permeable it only
allows SOME things through and not others


This represents a selectively permeable
membrane.
It allows (selects) certain things to pass
through it.

Is the membrane permeable to

Is the membrane permeable to
?
?

Molecules pass through the cell
membrane through:
› Passive Transport
 Diffusion
 Facilitated Diffusion
 Osmosis
› Active Transport
 Vesicles
 Pumps

Molecule- the smallest unit
of a compound/substance
› Cannot be seen with the
naked eye
› 1 drop of water has
16,700,000,000,000,000,000,000
molecules of H20
› 1 grain of salt has
120,000,000,000,000,000
molecules of salt

Concentration Gradientan area of high concentration next to an
area of low concentration
High
Concentration
of Molecules
Low
Concentration
of Molecules

Equilibrium is when there is an EQUAL amount
of molecules on each side of the membrane
There is no net movement
meaning, there is continuous
movement of molecules
back and forth through the membrane.

Passive Transport is when molecules
move from an area of HIGH
concentration to an area of LOW
concentration until equilibrium is
reached.
 Requires NO ENERGY!
 Examples:

› Diffusion
› Osmosis
› Facilitated Diffusion

Diffusion- the process by which
molecules (“stuff”) spread from
areas of high concentration, to
areas of low concentration

Molecules are said to go
“Down” or “with” the
concentration gradient.

Requires no energy
What will
Where
is the
happen
greatest
least
when
concentration
concentration
the gate is
of cows?
opened?
This process is called…
diffusion

Facilitated Diffusion
› What does facilitate mean?
› When substances move from high to low
concentration (down the concentration
gradient) using channel/carrier proteins
located in membrane
› Does not require energy
http://www.d.umn.edu/~sdowning/Membranes/diffusionanimation.html
Click, hold, and drag slider to move forward, bckword, or slow down
A special type of diffusion is called
osmosis
 Osmosis- the process by which WATER
molecules move from an area with a
high concentration of water to an area
of low concentration of water.

› OR the “diffusion of water”

Requires no energy

In Osmosis water will move in where there is
a low concentration of SOLVENT, and a
high concentration of SOLUTE
› A solute = “stuff” (salt, glucose, food particles)
› A solvent = “water”

There are three ways
water can move in a
solution:
› Hypotonic- water moves
INTO a cell and the cell
swells (gets bigger)
› Hypertonic – water moves
OUT of a cell and the cell
shrinks (gets smaller)
› Isotonic- water moves into
AND out of a cell at an
equal rate (remembermolecules are constantly
moving)

Hypotonic› Water moves into the
cell (and could burst)
› There is more
solvent/less solute on
the outside of the cell
than the inside
› So the solvent (water)
moves to an area of
low solvent (water)
concentration

Hypertonic› Water moves out of
the cell (and will shrink)
› There is less
solvent/more solute on
the outside of the cell
than the outside
› So the solvent (water)
moves to an area of
low solvent (water)
concentration
Isotonic- water moves
into and out of the
cell at equal rates
and stays the same
size
 So the concentration
of solvent and solute
on the inside of the
cell is equal to the
concentration of
solvent and solute on
the outside of the cell

Draw arrows to show the flow of water
 Label at the top if the solution is isotonic,
hypotonic or hypertonic

Where is the greatest
concentration of solvent?
Outside of the bag
Which way does the
water move?
Into the Bag
What type of
solution is this?
Hypotonic
selectively permeable membrane
Where is the greatest
concentration of
solvent?
In the bag
Which way does the
water move?
Out of the bag
90% water
10% salt
What type of solution is
this?
Hypertonic
selectively permeable membrane
What happens to
the bag?
90 % solvent
10% salt
selectively permeable membrane
What happens to
the bag?
90 % solvent
10% salt
selectively permeable membrane
What happens to
the bag?
90 % solvent
10% salt
selectively permeable membrane
What happens to
the bag?
The bag shrinks.
90 % solvent
10% salt
selectively permeable membrane

Passive transport:
› requires no energy
› moves from high concentrations to low
concentrations
› Moves down the concentration gradient
› Includes diffusion, facilitated diffusion and
osmosis

When molecules must move from a low
concentration to a high concentration
they must use active transport
› Cells must transport certain amino acids, sugars,
etc. into their cytoplasm from the surrounding
fluid.
› Some of these substances, however, are already
in higher concentrations inside versus outside.

This requires energy!
Opposite of Passive Transport
 Molecules go against the concentration
gradient
 Energy is provided by the ATP made in
the mitochondria
 Active transport can involve pumps or
vesicles
 Requires energy

Pumps allow molecules to travel against
their concentration gradient
 For example, the sodium/potassium
pump actively transports sodium
molecules and potassium molecules
through the cell membrane
 Requires energy

 Na+
pumped out of a cell
 K+ pumped into a cell
 Important because it
prevents cells from bursting
by lowering the sodium
inside causing less water to
enter through osmosis.
 Requires energy
Sodium Potassium Pump
Proton (H+) pump – forces protons out of a membrane
enclosed space (organelle or cell), often to create a
proton gradient down which the protons can flow back
in
Why would the cell “waste” energy on a proton pump?
*Because the cell needs isolated areas of the cell with
different pH for particular functions; ex) lysosomes –
have proton pumps to maintain a pH=5
*Because the cell only uses one ATP to pump a proton
out, and that proton can be used in co-transport
Co-transport – process cells use to bring large molecules,
such as sugars, into a cell with a minimum amount of
energy used; usually a proton and a sugar enter a
double tunneled protein at the same time; the tunnel
only “works” when both molecules are present

Vesicles can transport molecules across
the cell membrane through:
› Endocytosis- moving INTO the cell
› Exocytosis- moving OUT of the cell

Requires energy
Pinocytosis (drinking)
Phagocytosis (eating)
Exocytosis can help get rid of wastes or
secrete products like hormones or insulin
 Requires energy

Opposite of Passive Transport
 Molecules go against the concentration
gradient
 Energy is provided by the ATP made in
the mitochondria
 Active transport can involve pumps or
vesicles
 Requires energy
