Download Cell Transport: Moving molecules in and out of the cell

Cell Transport: Moving molecules
in and out of the cell
Plasma Membrane
Phospholipid
bilayer that
surrounds all
cells and certain
organelles
within the cell
Phospholipid
Hydrophilic Phosphate head
Hydrophobic Fatty acid Tails
Remember the Triglycerides?
What’s the difference?
In water what will happen?
Water on outside of cell
Water on outside of cell
Also Water on Inside of cell
Double layer allows:
• All hydrophobic parts to be
away from water
• All hydrophilic parts to be near
water
Membrane – more than just
phospholipids
A little more than just
phospholipids
Plasma membrane contains:
Proteins embedded in phospholipid bilayer;
Cholesterol tucked between fatty acids
Carbohydrate chains
Why proteins?
• Proteins increase contact with water
and act as channels through which
certain molecules can pass
Why cholesterol?
• Cholesterol affects fluidity. It stiffens
the membrane and prevents
solidification
Why Carbs?
Carbohydrate chains act as cell “ID”
tags.
Fluid Mosaic Model: theory that
describes the composition of the
membrane
- Fluid because it is flexible; p-lipids
and proteins can shift position
- Mosaic because it is made of many
small molecules that work together as
a whole
Membrane acts as a semi-permeable
barrier (think bouncer!)
some stuff passes right
through the phospholipids:
hydrophobic molecules
(O2, N2, CO2)
small polar molecules
(H2O)
some stuff stays out:
- ions (Na+, Cl-, K+, Ca++)
- small polar molecules (Sugars,
Amino Acids, H2O)
But don’t we need these?!?! We’re
getting there….
?
?
So what are the general factors that
determine how a molecule enters
the cell?
There are two general categories of
transport:
Passive transport: The easy way; no
energy required; molecules just flow
naturally across
Active Transport: the hard way;
energy required; molecules need to
be pushed or carried across
BROWNIAN MOVEMENT
Molecules are ALWAYS moving
Passive Processes: No energy
needed
• Diffusion: Movement of solutes
from areas of high concentration
to areas of low concentration until
concentrations are equal.
• Concentration Gradient =
differences in Concentration
Gaseous Diffusion
No membrane needed
High Conc.
Low Conc.
Think of it as molecules spreading
out!
Progression of Liquid Diffusion
High Conc.
Low Conc.
?
Facilitated Diffusion – movement of
solute from high concentration to
low concentration BUT requires
transport protein to move molecule
that are too big or polar to get
through the bilayer on their own
Glucose is too big to fit through
phospholipids and will be diffused
through a transport protein to get
into the cell
Osmosis – A Passive Process
where water moves across a
cell membrane from an area
that is hypotonic (lots of
water, little solute) to an area
that is hypertonic (little water,
lots of solute)
think of the water as trying to
dilute the concentrated side to
make the concentration even
Weak Iced Tea
Strong Iced Tea
Move water until you get
Two perfect Iced teas
Tonicity – term used to compare
the concentration of one solution
to another
- will determine where water
goes
3 Conditions
Hypotonic
Isotonic
Hypertonic
The solution with the higher
concentration is called Hypertonic.
The solution with the lower
concentration is called Hypotonic
If the concentrations are equal,
they are called isotonic
Which is
Hypertonic?
10% Salt Solution
20%
Salt Solution
Inside is Hypertonic
Which is
hypertonic?
20% Salt Solution
10%
Salt Solution
?
Outside is
Hypertonic
Isotonic:
20% Salt Solution
20%
Salt Solution
Isotonic
Crenation
Cytolysis
Comparing Cell types chart
Plasmolysis
Vs.
Turgidity in Plant cells
- Turgor pressure: Pressure that
the water INSIDE the cell puts on
the cell wall. Supports plant
A
B
A
B
Think about the cell membrane
• Transport proteins work a lot like
enzymes. The correct molecule “seats” it
self (even if no energy is required) and a
conformational change takes place.
• This doesn’t happen with the phospholipid
membrane. Things simply “pass through”.
The higher the concentration difference
the faster the rate of diffusion
Question:
• What will the graphs look like for the two
substances that are going through the cell
membrane?
• How is diffusion rate (facililated vs. simple)
impacted by the concentration of the
solute?
Active Transport
What is it: Cell must use energy to force
molecules to move across the membrane from
a low concentration to a high concentration.
When used: Usually used to move ions
AGAINST the gradient (remember that ions
can use facilitated diffusion with the gradient)
Active Transport: Ion Transfer
Example: Sodium:Potassium Pump Animation
Goal: maintain NON-EQUILIBRIUM concentrations of ions!
Found in: nerve cells
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_pota
ssium_pump_works.html
Vesicle Transport
Vesicle transport is different from
Diffusion
Osmosis
Facilitated diffusion
Active transport (using proteins) BECAUSE
We are moving large quantities (many molecules) rather than
individual molecules. The cell must package the material in a
vesicle and bring it in or out of the cell depending on the goal.
BULK Transport: the movement of large quantities at one time.
REQUIRES ATP
DOES NOT REQUIRE A Concentration Gradient
Types of Vesicle Transport
• The two types of vesicle transport depend
on direction –
• Moving materials into a cell in a vesicle is
called endocytosis.
• Moving materials out of a cell is called
exocytosis.
Bulk transport into cell
PHAGOCYTOSIS
(SOLIDS)
Endocytosis
PINOCYTOSIS
(LIQUIDS)
PHAGOCYTOSIS: “CELL EATING”
PROTEINS, BACTERIA, DEAD CELLS
ARE ENCLOSED IN A PL. MEMB. SAC.
NEEDS ATP
PINOCYTOSIS: “CELL DRINKING” PL.
MEMB. SINKS BELOW A FLUID
PARTICLE CONTAINING SMALL
SOLUTES AND FUSES WITH PL. MEMB.
FOMING A VESICLE
OCCURS IN MOST CELLS, EXP:
KIDNEYS AND INTESTINES
Exocytosis – Bulk Transport out of cell
Way of releasing large quantities of stuff from the
cell including : Hormones, mucus and cell wastes
NEEDS ATP