Transcript Hyponatremia Power Point

Water Can Kill?
Exploring Effects of Osmosis
by
Susan D. Hester
Department of Molecular and Cellular Biology
University of Arizona, Tucson, AZ
1
Membranes!
After this unit, you will be able to…
describe the structure and properties of a cell
membrane.
describe properties that affect how easily a
molecules can pass a pure phospholipid membrane.
predict how easily a molecules will be able to pass
a pure phospholipid membrane.
Phospholipid membranes are selectively
permeable
What are three
properties that affect
whether an atom/ion
or molecule can pass
easily through the
membrane?
Figure 6.7 from Biological Science, 4th
Edition by Scott Freeman, illustrating
where common molecules fall on the
permeability scale
Membrane properties depend on lipid
structure
Phospholipid bilayer membranes are fluid.
Figure 6.12 from Biological Science, 4th Edition by Scott
Freeman, illustrating phospholipids moving laterally in a
phospholipid membrane
A phospholipid can travel over the entire surface
of a small cell in a second!
Cell membranes are fluid
http://www.youtube.com/watch?v=jM_xePC70Yo
Membrane properties depend on lipid
structure
Examples of properties that effect membrane
permeability and fluidity:
length of the phospholipid fatty-acid tails
saturation of the phospholipid fatty-acid tails
cholesterol content
Membrane properties depend on lipid
structure
Long tails = more hydrophobic
interactions in the center of the
membrane  stiffer, less
permeable
Membranes with phospholipids
with short fatty-acid tails are more
fluid and permeable
Figure of phospholipid
membrane from Biological
Sciences, 4th Edition, by Scott
Freeman
Membrane properties depend on lipid
structure
Straight tails = more
hydrophobic interactions in the
center of the membrane  stiffer,
less permeable
Membranes with phospholipids
with kinked fatty-acid tails are
more fluid and permeable
Figure 6.10 from Biological
Science, 4th Edition, by Scott
Freeman
Membrane properties depend on lipid
structure
 carbons are saturated with hydrogen=straight tail
Double C=C
bond—carbons
NOT saturated
with hydrogen=
kinked tail
Figure 6.8 from Biological Science,
4th Edition, by Scott Freeman
Membrane properties depend on lipid
structure
Saturated tails = more
hydrophobic interactions in the
center of the membrane  stiffer,
less permeable
Membranes with phospholipids
with unsaturated fatty-acid tails
are more fluid and permeable
Figure 6.10 from Biological
Science, 4th Edition, by Scott
Freeman
Membrane properties depend on lipid
structure
The permeability and fluidity of membranes is
determined by the hydrophobic interactions in the
middle of the “lipid sandwich” of the membrane.
The more of the hydrophobic
fatty-acid “tails” that come into
contact with one another, the
stiffer and less permeable the
membrane.
Figure 6.10 from
Biological Science,
4th Edition, by
Scott Freeman
Cholesterol in cell membranes
Figure of cholesterol inserted into phospholipid bilayer
Diffusion and Osmosis
After this unit, we will be able to…
define the terms diffusion, tonicity and osmosis.
describe the molecular motions that lead to
diffusion.
predict the net movement of solute or water
molecules resulting from diffusion and osmosis.
discuss the importance of diffusion and osmosis
to cells and multi-cellular organisms.
Diffusion
This phenomenon is
known as diffusion—
solutes tend to spread
from areas of high
concentration to areas
of low concentration.
http://www.youtube.com/watch?v=THg4XqNyVMY
Diffusion
Diffusion is due to the random, undirected
motion of the solutes and surrounding water
Particles DON’T “know” they are in an
area of high concentration! –They do not
actively move away from it.
So how does it happen?
Brownian Motion
http://www.youtube.com/watch?v=6VdMp46
ZIL8
http://www.youtube.com/watch?v=2Vdjin734gE
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True or False? An individual solute molecule never
moves from an area of low concentration to an area
of high concentration
50%
50%
Fa
lse
Tr
u
e
A. True
B. False
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If the solutes can move across the membrane, what will
the net movement of solutes be in the situation below?
A. Into the liposome
B. Out of the
liposome
C. Neither into nor
out of the liposome
33%
A.
33%
B.
33%
C.
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Diffusion
Keep in mind:
Because diffusion is due to molecules being randomly
jostled around by the thermal motions of the molecules
around them, it takes a l-o-n-g time for particles to diffuse
much distance.
When molecules diffuse, they are not “trying” to get
anywhere—they don’t move in a straight line towards
anything.
Osmosis
Osmosis is a special case of diffusion—it happens
when there are solutes that cannot quickly pass
across the cell membrane and there is a higher
solute concentration on one side of the membrane
than the other.
When this happens, water will tend to diffuse to
the area of higher solute concentration (lower
“water concentration”).
Osmosis
Tonicity describes the balance (or imbalance) of
solutes in and out of the cell.
Hypertonic
Isotonic
Hypotonic
[solute] higher outside
[solute] equal inside
and outside
[solute] higher inside
If the solutes cannot move across the membrane, what
will the net movement of water be?
33%
33%
33%
A. Into the liposome
B. Out of the
liposome
C. Neither into nor
out of the liposome
A.
B.
C.
22
Osmosis
http://www.youtube.com/watch?v=dHc05E7BijQ
Membrane Transport Proteins
Not all movement across the cell membrane is
through the phospholipid bilayer—otherwise, cells
would be at the mercy of their environments.
Membrane transport proteins control passage of
certain substances across the membrane.
Which of the following would need a membrane
transport protein to cross the cell membrane at a
significant rate?
A.
B.
C.
D.
E.
F.
H2O
O2
Na+
C6H12O6 (glucose)
All of the above
C. and D.
17%
A.
17%
17%
17%
17%
B.
C.
D.
E.
17%
F.
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Membrane Transport Proteins
We will begin our discussion of cell structures
next week by talking about membrane proteins
including membrane transport proteins.
Water Can Kill?
You will now consider three true stories and
discuss/answer questions about what happened.
Please turn in one set of answers per group on a
separate sheet of paper.
You have 15 minute to complete Part I, after
which we will discuss Part I as a class.