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CELLULAR TRANSPORT
WATCH
• Building a cell membrane
INTRODUCTION
• The plasma membrane is responsible for
regulating materials that enter and exit the
cell.
• The cell must maintain homeostasis, the
regulation and maintenance of an
environment.
• Temperature, chemicals, water concentration,
and particle size have an effect on the rate of
transport through the membrane.
PLASMA MEMBRANE
FLUID MOSIAC MODEL
PLASMA MEMBRANE
Selective Permeability or Semipermeable:
– refers to
membrane’s
ability to
allow SOME
molecules
through and
others out.
PLASMA MEMBRANE
Peripheral proteins – do not go all the way through
Phospholipids
Integral
proteins –
go all the way
through
PLASMA MEMBRANE
• Imbedded Proteins - a variety of proteins
attached to the surface and embedded in the
membrane.
• Function: Each type of protein has a
specific purpose like ion channels, receptor
proteins, and proteins that allow cells to
connect to each other.
PLASMA MEMBRANE
• Peripheral Proteins - are proteins that
adhere only temporarily to the membrane.
• Function: Peripheral proteins allow many
molecules to be carried around the cell.
Some peripheral membrane proteins carry
molecules between other proteins.
PLASMA MEMBRANE
REMINDERS
• Selectively permeable: choosy as to what gets in and
out of cell. Also semipermeable.
• Phospholipid bilayer: double layer of phospholipids.
• Hydrophilic head: (polar). Water-loving. Carboxyl
end of the fatty acid.
• Hydrophobic tail: (nonpolar). Water-fearing.
Hydrocarbon chain of the fatty acid.
PHOSPHOLIPID BILAYER
TRANSPORT
• Cell membranes allow nonpolar molecules
such as O2 and CO2 slip across.
• Water molecules sometimes pass.
• Large, polar molecules cross with the help
of embedded proteins.
TRANSPORT
• Molecules or ions move constantly,
randomly colliding trying to reach
equilibrium.
• When dynamic equilibrium is reached, the
same amount of molecules will move into
and out of the cell.
• The rate depends on size of particle,
temperature, composition of solution.
TRANSPORT
• When the concentration in one region is not
the same as in an adjoining region, this
condition is a concentration gradient “THE FORCE”
– The steeper the gradient the faster the diffusion.
– Increased temperature increases the rate of
diffusion. Ex: sugar dissolved in hot tea.
– Increased pressure increases the rate of
diffusion. Molecules have more collisions
under high pressure.
EQUILIBRIUM
HOMEOSTASIS
• Homeostasis is the property in which
variables are regulated in a system so that
internal conditions remain stable and
relatively constant.
• Examples include the regulation of
temperature and the balance between acidity
and alkalinity (pH).
• Homeo (“like”) + stasis (“standing still”)
TO DO
• Do Section A now.
PASSIVE TRANSPORT
• No energy required to move down the
concentration gradient.
• Movement from high to low concentration.
• TYPES of passive transport:
1) Osmosis
2) Diffusion
3) Facilitated Diffusion
WATCH
• Diffusion and Osmosis
OSMOSIS AND DIFFUSION
SECTION D
In this lab you will observe the diffusion of
a substance across selectively permeable (or
semipermeable) membrane.
The dialysis tubing is selectively permeable
like a cell membrane allowing smaller
molecules to pass through easily.
Iodine is an indicator for starch and will
turn from reddish brown to dark black in the
presence of starch.
PROCEDURE
1. Tie one end of the dialysis tubing in a knot.
2. Add one scoop of cornstarch and water in the
dialysis bag. Do NOT fill the bag full.
3. Tie a knot in the other end of the dialysis tubing.
Leave some air in the tubing. Wash the tubing off
to remove cornstarch from the outside of the bag.
4. In a cup, add water to fill the cup ½ full. Place 5
drops of iodine into the water filled cup.
5. Place the tubing in the cup of water. Let it sit for
ten minutes and answer the questions below while
you wait.
WHILE WE ARE WAITING
Answer the pre-lab questions (1-4) now.
Pre-lab questions:
1. What is in the tubing? What color is it?
2. What is in the cup? What color is it?
3. What do you predict will happen to the
iodine and cornstarch molecules?
(Hypothesis)
4. How is the tubing similar to a cell
membrane?
Osmosis
OSMOSIS
• movement of H2O from high to low
concentration
• Water makes up 70% to 95% of a cell.
• The cell has no control over osmosis.
Water will flow into and out of the cell until
equilibrium is reached.
OSMOSIS
PASSIVE TRANSPORT
• Osmosis
DIFFUSION
• Movement of particles from a high to a low
concentration.
• Example: drop of food coloring in water Diffusion will continue until the molecules of food
coloring are evenly distributed.
DIFFUSION
DIFFUSION
• One of the major mechanisms of molecular
transport in cells.
• Oxygen and Carbon Dioxide diffuse readily
through the cell membrane.
• Living cells maintain a balance by
regulating what enters and leaves the cell.
• Without this ability, cells cannot maintain
homeostasis and will die.
GAS EXCHANGE IN THE
LUNGS
PASSIVE TRANSPORT
• Diffusion
glucose transporter
solute (glucose)
Passive Transport
high
low
Stepped Art
Figure 5.10
Page 88
OSMOSIS AND DIFFUSION
LAB
Do the Post-Lab questions
• What is in the tubing? What color is it?
• What is in the cup? What color is it?
• Which molecule(s) diffused across the
membrane?
• Explain the movement of the molecule(s).
• Is this active or passive transport? How did
you know?
FACILITATED DIFFUSION
• Use of transport molecules to diffuse particles.
• When carrier proteins are used to transport
substances such as amino acids & sugars across
the membrane down the concentration gradient.
• Substances are moving from high to low
concentration, no energy is expended, so this is
passive transport.
FACILITATED DIFFUSION
Different ways it can happen:
• Carrier proteins: transport large molecules across
the membrane, very specific. Ex: Glucose.
• Bind, carry, and release. Protein molecule
changes shape and shields molecule from the
interior of the lipid bilayer.
FACILITATED DIFFUSION
GATED CHANNELS
• Ions & most polar molecules cannot diffuse across the
membrane because they cannot pass through the nonpolar
interior of the lipid bilayer.
• Substances can cross when aided by Carrier proteins.
• Transport proteins called channels provide polar
passageways though which ions & polar molecules can
move across the membrane.
• Ions are moving down the concentration gradient, so no
energy is expelled, making this process a form of passive
transport. Ion charge also has an affect on movement.
• Ions such as Na+, K+, Ca+2, & Cl- pass through ion
channels, a doughnut-shaped transport protein with a polar
pore.
ION CHANNEL
PASSIVE TRANSPORT
ACTIVE TRANSPORT
• Energy is required to move against the
concentration gradient.
• Movement from low to high concentration.
• Moving molecules against the concentration
gradient requires the use of energy (ATP).
• TYPES of Active Transport:
1. Membrane transport proteins
2. Endocytosis
3. Exocytosis
MEMBRANE TRANSPORT
PROTEINS
SODIUM-POTASSIUM PUMP
Transports three Na+ ions out of the cell, and two K+ ions into
the cell against the concentration gradient.
• Pump prevents Na+ from accumulating in the cell, which
would be toxic. If not controlled, this would cause water
to enter the cell by osmosis and cause the cells to burst.
• The Na+-K+ pump creates an electrical gradient that is
important to many physiological processes in animals,
such as nerve conduction & muscle contraction.
SODIUM-POTASSIUM PUMP
BULK TRANSPORT
Requires energy, so active transport.
2. Endocytosis: materials are engulfed by enclosing the cell
membrane around a substance forming a pouch or a vesicle
and being brought inside the cell. Two types:
- Pinocytosis: movement of liquids with solutes or small
particles.
- Phagocytosis: Movement of large particles, solids, or
whole cells.
3. Excocytosis: Materials inside cell are excreted out of the
cell. The vacuole, or vesicle, fuses with the cell membrane,
dumping contents into the external environment.
ENDOCYTOSIS
EXOCYTOSIS
Exocytosis
Endocytosis and
Exocytosis
plasma membrane
cytoplasm
Endocytosis
cytoplasm
ACTIVE TRANSPORT
Active Transport
higher calcium
concentration
Active Transport
lower calcium concentr
ATP
Pi
AD
P
Stepped Art
Figure 5.11
Page 89
TO DO
• Do Sections B and C now.