Transcript cell membrane

Cell Transport
copyright cmassengale
1
Check Your Understanding
At the end of today’s lesson, you should be able to
answer the following questions:
• What are the parts of the cell membrane and what do
they do?
• What is the “Fluid Mosaic Model?”
• Describe the processes of diffusion, osmosis,
facilitated diffusion, and active transport.
Cell Membrane
Regulates passage of
materials into and out of
the cell
Parts of the membrane:
A) lipid bilayer (2 layers)
B) proteins
C) cholesterol
D) carbohydrate chains
copyright cmassengale
3
Lipid Bilayer
• Made of 2 sheets of
phospholipids, a type of lipid
with a head and 2 tails
• Hydrophilic (water loving)
head
• Hydrophobic (water fearing)
tail
copyright cmassengale
4
Why do the phospholipids arrange
themselves in a bilayer?
copyright cmassengale
5
• Membrane Proteins: Act as
channels for large particles
to enter and leave the cell
• Fluid-Mosaic Model:
describes the flexibility of the
lipid bilayer with a mosaic of
proteins and other molecules
..\..\..\Downloaded Videos\Fluid mosiac
model.avi
6
Carbohydrate Chains
• Recognize parts of molecules to
determine what molecules can be
brought into the cell
• Can be attached to proteins or
phospholipids
• Lock and Key Fit!
Label the Parts of the Membrane!
•
•
•
•
•
Outside cell
Inside cell
Phospholipid
Protein
Carbohydrate Chain
Function of the Cell Membrane
• Regulates what enters and leaves the
cell
• Provides protection and support
Random Transition…AHHHH!
• This may seem completely rando…but I
promise the dots will connect later!
Concentration
• In a solution, the concentration is the
mass of solute in a given volume of
solution
• A difference in concentration over a
distance is called a concentration
gradient
Simple Diffusion
• Description:
Molecules move from
area of HIGH to LOW
concentration
• This means they are
going DOWN the
CONCENTRATION
GRADIENT
• PASSIVE Process (no
energy required)
13
..\..\..\Downloaded Videos\Diffusion.avi
14
Simple Diffusion of a Solute
Across a Membrane
copyright cmassengale
15
Can all solutes cross the
membrane by simple
diffusion?
• NO!
• The membrane is selectively
permeable, this means only certain
solutes (typically small ones) can pass
across by simple diffusion
• The solution? – Channel Proteins!
copyright cmassengale
16
Facilitated Diffusion
• Description: Diffusion of certain molecules
through a selectively permeable membrane,
made possible by protein channels
• PASSIVE Process
• DOWN gradient
..\..\..\Downloa
ded
Videos\facilita
ted
diffusion.avi
Osmosis
• Description: Diffusion of WATER across a
selectively permeable membrane
• PASSIVE process
• DOWN GRADIENT (that is, WATER moves
down its gradient)
..\..\..\Downloaded
Videos\Osmosis.avi
18
Cell in Isotonic Solution
10% solute
ENVIRONMENT
90% water
CELL
10% solute
90% water
What is the direction of water movement?
The cell is at EQUILIBRIUM.
Solution outside
the cell has the
SAME solute
(and water)
concentration as
the cell itself
Cell in Hypotonic Solution
10% solute
ENVIRONMENT
90% water
CELL
20% solute
80% water
Solution outside
the cell has a
LOWER solute
(HIGHER water)
concentration
than the cell
itself
What is the direction of water movement?
20
Cell in Hypertonic Solution
15% solute
85% water
ENVIRONMENT
CELL
5% solute
95% water
Solution outside
the cell has a
HIGHER solute
(LOWER water)
concentration
than the cell
itself
What is the direction of water movement?
21
Isotonic Solution
NO NET
MOVEMENT OF
H2O (equal amounts
entering & leaving)
Hypotonic
Solution
Cell Bursting
..\..\..\Download
ed Videos\Red
Blood Cells in
Hypotonic
Solution.avi
Hypertonic
Solution
Cell Shrinking
..\..\..\Downloaded
Videos\Onion Cells
Plasmolysis.avi
..\..\..\Downloaded
Videos\Red Blood Cells in
a Hypertonic Solution.avi
Osmosis in Red Blood Cells
Isotonic
Hypotonic
copyright cmassengale
Hypertonic
23
Osmosis in Plant Cells
Active Transport
• Description: Movement of
materials from LOW to HIGH
concentration
• ACTIVE process (uses energy)
• UP Concentration Gradient
Active Transport
Molecular Pumps
Molecular pumps are
membrane proteins
that use energy from
ATP to move
molecules across cell
membranes. (Each
pump moves one type
of molecule)
..\..\..\Downloaded Videos\Active
Transport.avi
ATP
Endocytosis vs. Exocytosis
• Endocytosis: taking large amounts of
material into the cell
• Exocytosis: sending large amounts of
material out of the cell
copyright cmassengale
27
Endocytosis:
Phagocytosis & Pinocytosis
Phagocytosis: The
membrane folds to
enclose solid particle
(cell eating)
Pinocytosis: The
membrane folds to
enclose liquid with
dissolved materials (cell
drinking)
• In endocytosis,
the membrane
pinches in to
form a vesicle
• The vesicle may
later join with a
lysosome so that
particles can be
“digested”
Vesicles
copyright cmassengale
29
Exocytosis
1
Products of the ER are
packaged in vesicles
at the Golgi and
released at the cell
membrane.
..\..\..\Downloaded
Videos\Endocytosis &
Exocytosis.avi
Cell Membrane and Homeostasis
• Refresher from Characteristics of
Life…what is homeostasis?
• How does the cell membrane help
organisms to maintain homeostasis?