Cell Membrane
and what it does
for the cell.
Phospholipid Bilayer
Synonyms
• Plasma Membrane
• Cell Membrane
• Phospholipid Bilayer
Membrane up close
• Hydrophobic
– Hydro
– Phobic
– Repels water
• Hydrophilic
– Hydro
– Philic
– Loves water
Phospholipid Up Close
Insane in the Membrane – things
on the membrane
• Carbohydrate Chain –
acts like an
identification tag for the
cell
• Protein Channels –
used to transport
molecules in and out of
the cell
• Proteins – transmit
and receive signals to
other cells
Types of Transport
Across Cell
Membranes
Transport through membranes
• 2 ways
– Passive transport: movement of substances
across a membrane
• Does not use energy
• Examples: Diffusion, Osmosis, Facilitated Diffusion
– Active transport: movement of molecules
(or larger particles) through the cell
membrane
• Uses energy
• Examples: Na+/K+ Pump, Endocytosis, Exocytosis
Diffusion
• Molecules move
from area of HIGH
to LOW
concentration
• NO energy
required
What is the goal of diffusion?
Diffusion of Liquids
Facilitated Diffusion
• Movement of specific molecules through
proteins channels
• Why called facilitated?
• Types of Proteins that move molecules
– Carrier and Channel
Types of Proteins
• A) Channel Protein – doesn’t change
shape
• B) Carrier Protein – changes shape
Osmosis
• Water moves from
HIGH concentration
(low solute) to LOW
concentration (high
solute) concentration
• Diffusion of water
across a semimembrane
Diffusion across a membrane
Semipermeable
membrane
Diffusion of H2O Across A
Membrane
High H2O potential
Low solute concentration
Low H2O potential
High solute concentration
Ultimate Goal of
Diffusion and Osmosis
• Reach a state of DYNAMIC EQUILIBRIUM
– and ultimately have HOMEOSTASIS.
– Dynamic Equilibrium – continuous movement
of molecules across the membrane, but there
is no change in concentration.
– Homeostasis – body’s attempt to maintain
stable internal conditions.
Types of Solutions
• Hypotonic
– Hypo
• Hypertonic
– Hyper
• Isotonic
– Iso
What happens when you put cells
in different types of Solutions?
• Cell on left is a typical sample of red blood cells.
• Cells on the right have been put in a hypotonic solution. If
left there long enough, the cells will burst open. Water from
the solution is moving into the cells.
What happens when you put cells
in different types of Solutions?
• Cell on left is a typical sample of red blood cells.
• Cells on the right have been put in a hypertonic solution.
The cells have lost water and are starting to shrivel.
Cell in Hypotonic Solution
10% NaCL
90% H2O
CELL
20% NaCL
80% H2O
What is the direction of water movement?
Cells in a Hypertonic Solution
15% NaCL
85% H2O
ENVIRONMENT
CELL
5% NaCL
95% H2O
What is the direction of water movement?
Cell in Isotonic Solution
10% NaCL
90% H2O
ENVIRONMENT
CELL
10% NaCL
90% H2O
NO NET
MOVEMENT
What is the direction of water movement?
equilibrium
The cell is at _______________.
Active Transport – movement
across the membrane with Energy
• ATP is the cell’s energy
• What organelle do you
think would make ATP in
your cells?
• ATP is used in Active
Transport
Why do some types of transport
need energy?
• Active Transport moves molecules from
LOW concentrations of solutes to HIGH
concentrations of solutes.
– We call this moving AGAINST the
CONCENTRATION GRADIENT.
– In Diffusion and Osmosis – molecules move
WITH the CONCENTRATION GRADIENT.
Na+/K+ ATPase Pump
• 3 Na+ move out and ATP binds to protein – causes
the protein to open up to the outside of the cell.
• This allows 2 K+ to enter the cell. ADP can bind to
its other Phosphate to become ATP.
• Purpose of this pump – maintain Na+ and K+
levels inside and outside of the cell.
Na+/K+ ATPase Pump
• Another use
– Glucose sometimes has to enter the cell even when
the concentration of glucose inside the cell is really
HIGH, so ENERGY is needed.
– When the 3 Na+ get pushed outside of the cell in
the pump, they can reenter the cell if they tag along
with a Glucose molecule and enter through a
channel protein – this is called COUPLING – when
2 different molecules use the same protein channel
at the same time.
Endocytosis - Active
Exocytosis - Active
Links for Concepts in Motion
http://glencoe.mcgrawhill.com/sites/0078802849/student_view0/unit2/c
hapter7/concepts_in_motion.html#