Biophysics I - OSMOSIS
04/11/2014
Andrea Vig
University of Pécs, Medical School,
Department of Biophysics
28/10/2014
 BROWNIAN MOTION
OSMOSIS,
MEMBRANETRANSPORT
OVERVIEW – DIFFUSION
random thermal motion of particles
 DIFFUSION
due to the non-uniform (inhomogeneous) distribution of particles
net transport of particles (Brownian motion) occurs from a region of higher concentration to a region of lower
concentration which continues until the distribution of particles is uniform (homogeneous)
 FICK’S 1st LAW (spatial description)
∆𝒄
Onsager’s equation (linear, irreversible processes): J=XL The flow density of the extensive quantity (J)
𝑱 = −𝑫
is linearly proportional to the gradient of the intensive quantity (X)
∆𝒙
 DIFFUSION COEFFICIENT: Stokes-Einstein equation
𝒌𝑻
𝑫=
𝟔𝝅𝜼𝒓
 FICK’S 2nd LAW (spatial & temporal description)
∆𝑐
∆( )
∆𝑐
= 𝐷 ∆𝑥
∆𝑡
∆𝑥
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Biophysics I - OSMOSIS
04/11/2014
OSMOSIS IN THE KITCHEN
Experiment: place a dried leaf of salade into water
before
Osmosis in the k itchen.mp4
after (3-4 hours)
Observation: the leaf of salad becomes bigger and looks fresh again
OSMOSIS
Experiment: place an egg into corn syrup then into water
WATER
CORN SYRUP
Observation : the egg shrinks
Observation: the shrinked egg gains its original
size, and it continues to get even bigger
after
before
before
after
Experiment: fill a small-size semi-permeable bag with sugar dissolved in water, and placed in a
water filled container
Observation : the bag is swelling, the water surrounding
sugar solution
water
it remains pure, sugar solution has been diluted
before
after
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Biophysics I - OSMOSIS
04/11/2014
What is the difference between the „ink” experiment and the
„salade/egg/sugar” experiment?
OSMOSIS
1. SOLID (non-permeable) WALL (as Fick’s experiment)
fluid→gas (no complicated molecular interactions)
A+B components, we usually ignore one, and examine the distribution of
the other
x (distance)
NO TRANSPORT
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04/11/2014
OSMOSIS
2. NO WALL
t (time)
Biophysics I - OSMOSIS
x (distance)
free DIFFUSION
both particles (smaller/larger) reach homogeneous distributions
OSMOSIS
3. SPECIAL WALL
restricted DIFFUSION: OSMOSIS
smaller molecules reach a uniform distribution
larger molecules remain in the compartment
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Biophysics I - OSMOSIS
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OSMOSIS
3. SPECIAL WALL
SEMIPERMEABLE – „filter”
semi-permeable membrane
allows smaller slovent molecules to pass through, but not the larger solute molecules
PORE DIAMETER  SELECTIVITY
animal skin pellicles, walls of living cells, ceramic plate with holes, cellophane
OSMOSIS –types of walls, summary
type of the wall
yes: non-permeable
no
yes: SEMIPERMEABLE
matter transport
no
free diffusion
restricted diffusion: OSMOSIS
OSMOSIS:
unidirectional matter flow, which takes place by means of
diffusion
semipermeable wall + concentration difference
(from the perspective of osmosis, the dissolved substance’s qualities are irrelevant)
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Biophysics I - OSMOSIS
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QUANTIFICATION OF OSMOSIS
h
semisugar
solution permeable
membrane
water
J OUT
J OUT
J IN
J IN
solvent
r: density
h: height
g = 10 m/s2
solvent
+ solute
mixture
semipermeable membrane
-solvent flow throught the
semipermeable membrane
-concetration difference
-dynamic equilibrium
OSMOTIC EQUILIBRIUM
-semipermeable membrane:
allows solvent to pass through but
not the solute
-the volume of the solvent +
solute mixture increases
HYDROSTATIC PRESSURE
(ph)
-solvent flow slows down
OSMOTIC PRESSURE
J OUT
J OUT
J IN
J IN
OSMOTIC PRESSURE
 pressure that has to be exerted on the solution connected to pure solvent by a
semipermeable membrane to reach dynamic equilibrium, to counteract osmosis
 pressure that inhibits the net solvent flow
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Biophysics I - OSMOSIS
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OSMOTIC PRESSURE
VAN’T HOFF’s LAW
for dilute solutions and perfect semipermeable membranes using the equation of state of
2.
1.
the ideal gas
𝒑osmotic = 𝒄𝑹𝑻
cred
V: volume
𝑛𝑟𝑒𝑑
n: mole fraction
𝑅𝑇
p1-p2=posmosis=
𝑉
T: temperature
c: concentration
R: universal gas constant
pV=nRT
nblue1=nblue2
p1=
𝑛𝑟𝑒𝑑+𝑛𝑏𝑙𝑢𝑒1
𝑅𝑇
𝑉
p2=
𝑛𝑏𝑙𝑢𝑒2
𝑅𝑇
𝑉
𝒑ozmózis ~𝒄
the osmotic pressure is linearly proportional to the concentration
OSMOTIC PRESSURE
 upon OSMOSIS the net particle transport occurs from the lowconcentration regions (of the solute!!!!!) (low osmotic pressure) to
the high-concentration regions (high osmotic pressure)
from low osmotic pressure→high osmotic pressure
 it is always the more dense solution which becomes diluted
OSMOSIS
1.
2.
solvent
solvent
+ solute
mixture
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Biophysics I - OSMOSIS
04/11/2014
CLASSIFYING SOLUTIONS ON THE BASIS OF OSMOTIC PRESSURE
HYPERTONIC
ISOTONIC
HYPOTONIC
higher concentration
same concentration
lower concentration
c > cx
c = cx
c < cx
higher osmotic pressure
same osmotic pressure
lower osmotic pressure
p > px
p = px
p < px
for the cells of the human body,
blood:
 0.87 % (0.15 M) NaCl
physiologic saline solution
 3.8 % sodium citrate
 5.5 % (0.3 M) glucose
x: reference
RED BLOOD CELLS IN DIFFERENT ENVIRONMENT
HYPERTONIC
(more concentrated: 10% NaCl)
ISOTONIC
(0.87 % NaCl)
pout > pin
pout = pin
net water OUTflux
NO net water flux
HYPOTONIC
(less concentrated: 0.01% NaCl)
pout < pin
net water INflux
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Biophysics I - OSMOSIS
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RED BLOOD CELLS IN DIFFERENT ENVIRONMENT
HYPOTONIC
IZOTONIC
HYPERTONIC
Role of osmosis in the life of plant cells
PLANT CELLS IN DIFFERENT ENVIRONMENT
net water OUTflux
PLASMOLYSIS
plasma membrane is pulled
away from the cell wall
NO net water flux
net water INflux
TURGOR PRESSURE
plasma membrane is pushed to
the cell wall
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Biophysics I - OSMOSIS
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OSMOSIS IN THE MEDICAL PRACTICE
1. INJECTION, INFUSION
 drugs are dissolved in physiological saline solution
 isotonic environment (compared to the body fluid)
water outflow
2. TREATMENT OF OEDEMAS, INFLAMED AREAS
 abnormal accumulation of fluid beneath the skin or in one or more cavities
of the body that produces swelling (fluid accumulation)
 dextran-solution/bitter salt (MgSO4-solution)-based treatment
 hypertonic environment is created (compared to the swollen areas)
 induces water outflow from the swollen areas
 reduced swelling
hypertonic
water influx
3. TREATMENT OF CONSTIPATION - LAXATIVE SALTS
 laxative salts are not absorbed by the large intestine
 hypertonic environment is created in the large intestine
 results in water influx into the large intestine
 dilution of colonic content, facilitated excretion
hypertonic
OSMOSIS IN THE MEDICAL PRACTICE
4. DIALYSIS
 different particles can be sorted by semipermeable membranes
 pore size of the membrane determines which molecules can pass
through the membrane
dialysis bag
semipermeable membrane
concentrated solution
t=0s
t
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Biophysics I - OSMOSIS
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OSMOSIS IN THE MEDICAL PRACTICE
4.1. HAEMODIALYSIS
 treatment of patient with severe kidney disease
 remove soluble chemicals toxic for the body (protein products, toxins, other waste
products exit with water, essential plasma proteins, cellular elements of blood
remain),
Schematic diagram of haemodialysis („artificial kidney” instrument).
essential element:long
semi-permeable membrane
(cellophane), surrounded
by dial.solution
average treatment time:
4-8 h
protein products
toxins
other waste products
dial.solution has to be
changed frequently
check ion-concentrations
and metallic-ioncontaminations in the solution
OVERVIEW
• Osmosis
• Van’t Hoff’s law
• Osmotic pressure and its significance (rbc, medical application)
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Biophysics I - OSMOSIS
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MEMBRANE STRUCTURE, MEMBRANETRANSPORT
MEMBRANE STRUCTURE
Biological membranes consists of lipids and proteins to bind with non-covalent bond.
Phospholipids are the main components of biological membranes.
Phospholipid = diglyceride (1 glycerole + 2 fatty acids) + phosphate group + organic molecule
(e.g. choline)
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Membrane-models
Irving Langmuir was an American chemist and
Lipid-soluble
substances
physicist. 1932
– Nobel enter
prize the cell quickly.
Fats are arranged in a layer on the surface.
Benzine-lipid mixture, the evaporation of petrol a
molecular lipid film is formed.
Petrol – soluble lipids form lipid bilayer on the surface
of the water.
1925 Lipid bilayer
The proteins are an integral part of cell membrane. The
lipid bilayer. Partly explains the proteins, sugars, ions and
other hydrophilic substances fast passage.
Discovery of Electronmicroscope.
The cells are covered by plasmamembrane.
„Unit-membrane”model.
Mosaic-like
1972
„ Fluid arrangement
mosaic” modelof
proteins in the membrane.
Transmembrane proteins.
Dr. habil. Kőhidai László
FLUID MOSAIC MODEL
Singer – Nicolson
1972
Membrane of erythrocyte
http://www.youtube.com/watch?v=ZP3i5Q9XfTk
http://www.youtube.com/watch?v=oq4Um1oV4ag
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Biophysics I - OSMOSIS
04/11/2014
STRUCTURE OF THE CELL MEMBRANE
MEMBRANE PROTEINS

These proteins determine the function of the membranes.

The types of membrane proteins:





Transmembrane proteins – It can bind to the hydrophobic part of the
membrane.
Peripheral membrane proteins– not directly linked to the membrane.
Glycoproteins - these oligosaccharides are attached to the extracellular side of
the membrane proteins.
Glycosyl-phosphatidylinositol (GPI) - are covalently bonded to the
membrane’s lipids.
Roles:



Ion channels
Receptors
Signal transduction
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Biophysics I - OSMOSIS
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Example 1: DIFFUSION THROUGHT THE CELL MEMBRANE
EXTRACELLULAR
SPACE
MATTER
TRANSPORT
LIPID BILAYER
MEMBRANE PROTEINS
water
apolar molecules
ions
monosaccharides
amino acids
metabolites
INTRACELLULAR SPACE
cytoplasm
different mechanism: exocytosis and endocytosis
DIFFUSION THROUGH THE CELL MEMBRANE
TRANSPORT PROCESSES ACROSS BIOLOGICAL MEMBRANES
I. TRANSPORT MECHANISM
WITHOUT MEDIATOR
WITH MEDIATOR
PASSIVE DIFFUSION
ion channels
1.
2.
FACILITATED DIFFUSION
carrier proteins
carrier proteins
3.
PASSIVE TRANSPORT
4.
ACTIVE TRANSPORT
II. ENERGETIC REQUIREMENTS
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DIFFUSION THROUGH THE CELL MEMBRANE
1. PASSIVE DIFFUSION
Passive transport
Without mediator
 direction of transport:ELECTRO-CHEMICAL POTENTIAL GRADIENT
 chemical potential gradient (concentration)
 electric potential gradient (charge)
 rate of diffusion: Fick’s laws
 mediator: no
 energetic requirement: no
 examples:
 hydrophobic molecules: O2, N2
 small polar molecules: CO2, water, alcohol, urea, glycerol
 glucose, sacharose
DIFFUSION THROUGH THE CELL MEMBRANE
2. FACILITATED DIFFUSION
Passive transport
With mediator: ION-CHANNEL
 direction of transport: chemical or electro-chemical potential gradient
 rate of diffusion: faster than that expected from Fick’s laws
 mediator: ION-CHANNEL PROTEIN
 transmembrane proteins
 closed / open state: no transport / transport
 regulation:
 mechanically-gated (mechanical tension)
 voltage-gated (potential difference)
 ligand-gated (ligand-binding)
 selectivity: size & charge of the ions
 energetic requirement: no
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Biophysics I - OSMOSIS
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DIFFUSION THROUGH THE CELL MEMBRANE
3. FACILITATED DIFFUSION
Passive transport
With mediator: CARRIER PROTEINS
 direction of transport: chemical or electro-chemical potential gradient
 rate of diffusion: faster than that expected from Fick’s laws
 mediator: CARRIER PROTEIN
 specifically binds the ions or molecules and promotes their transport
 energetic requirement: no
DIFFUSION THROUGH THE CELL MEMBRANE
4. FACILITATED DIFFUSION
Active transport
With mediator: CARRIER PROTEINS
 direction of transport: AGAINST the chemical or electro-chemical potential gradient
! ENERGY IS REQUIRED
 mediator: CARRIER PROTEIN
 uniporter
 symporter/antiporter
 energetic requirement: yes
 ATPase transporter (ATP hydrolysis)
 photo transporter (light energy)
 coupled transporter (energy from an other transport)
 example: Na+-K+ pump
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