Transcript Plasma Membrane Transport

Plasma Membrane Transport
Cells
Fluid Mosaic Model
Phospholipid
Cholesterol -immobilizes phospholipids
(makes membranes less fluid and stronger)
Membrane Protein Functions
Passive Transport
• Requires no energy
• Occurs due to natural concentration gradient
• Molecules move from high concentration to low
concentration (DOWN the gradient)
3 Types
 Diffusion
 Osmosis
 Faciliated Diffusion
Diffusion
Diffusion
• A.K.A. simple diffusion
• Movement of small molecules across a selectively
permeable membrane from an area of HIGH
concentration to an area of LOW concentration w/o the
use of energy (DOWN the concentration gradient)
e.g. O2, CO2, urea, & alcohol
Osmosis
The diffusion of WATER across a selectively
permeable membrane
OSMOTIC PRESSURE
The pressure exerted on plasma membranes in solution
• Isotonic solution
• Hypertonic solution
• Hypotonic solution
Water Potential
• The physical property predicting the direction in
which water will flow, controlled by the solute
concentration
(ψ) = Greek letter psi
(ψ)
Water potentials
are a way of measuring the free-energy of water.
Water will flow spontaneously from a high potential to a low potential,
like a ball rolling down a hill.
Physical pressure due to
air & the container
Ho w So l u t e Co n c en t r a t i o n Af f ec t s
Wa t er Po t en t i a l
12
Wa t er Po t en t i a l
10
8
6
4
2
0
1
2
3
4
5
6
7
8
So l u t e Co n c en t r a t i o n
9
1
11
Cells in Isotonic Solution
Isotonic Solutions
• If the concentration of solute (salt) is =
on both sides, there will be no net
movement of water
• "ISO" means the same
Cells in Hypertonic Solution
Hypertonic Solutions
• More solute (salt) molecules outside the cell, which
causes water to be sucked out of the cell.
• In plant cells, the central vacuole loses water and the
cells shrink, causing plasmolysis resulting in the
plant wilting.
• In animal cells, the cells also shrink.
• In both cases, the cell may die.
• This is why it is dangerous to drink sea water
Plasmolysis
A phenomenon in plant cells in which the cytoplasm
shrivels and the plasma membrane pulls away from
the cell wall when the cell loses water to a hypertonic
environment.
Cells in Hypotonic Solution
Hypotonic Solutions
• There are less solute (salt) molecules outside the
cell, since salt sucks, water will move into the cell.
• The cell will gain water and grow larger. In plant
cells, the central vacuoles will fill and the plant
becomes stiff and rigid, the cell wall keeps the
plant from bursting
• In animal cells, the cell may be in danger of
bursting, organelles called CONTRACTILE
VACUOLES will pump water out of the cell to
prevent this.
Osmotic Potential
The tendency of water to move across
a selectively permeable membrane into
a solution
Determined by measuring the pressure
required to stop the osmotic
movement of water into the solution.
Osmosis Review
Facilitated Diffusion
Protein Channel or Pore
Facilitated Diffusion
Protein Carrier
Active Transport
• Requires cell energy (ATP) to move molecules
AGAINST the concentration gradient; from an
area of LOW concentration to an area of HIGH
concentration
• Sodium–Potassium pump (Exchange 3 sodium
ions for 2 potassium ions)
• Hydrogen ion, or proton pump (Pump hydrogen
ion against the concentration gradient)
Phosphorylation
The addition of a phosphate (PO4) group
(From ATP) to a protein or a small molecule
This changes the protein shape
Active Transport (Uniport)
Active Transport Na-K Pump
Na-K Pump Antiport
Glucose-Sodium Symport
Proton (Hydrogen Ion) Pump
Bulk Media Transport
• Endocytosis – Vesicle is created from the invagination of the plasma
membrane, which pinches off, bringing large molecules into the cell
• Pinocytosis – Cell drinking (endocytosis)
• Phagocytosis – Cell eating (endocytosis)
• Receptor Mediated Endocytosis – Substrate binds to receptor found
on the plasma membrane to be brought into the cell
• Exocytosis – Vesicle binds to the plasma membrane releasing the
contents outside of the cell
Endocytosis
Pinocytosis
Phagocytosis
Receptor Mediated Endocytosis
Exocytosis