Download File - Down the Rabbit Hole

CELLS
MOVEMENT ACROSS THE
MEMBRANE
Plasma Membrane
STRUCTURE
• This is the boundary between
the cell cytoplasm & the
environment
• Is selectively permeable
• Here we see a cross section of
the cell membrane you should
notice two different structures:
The phospholipids are the
round yellow structures with
the blue tails
The proteins are the lumpy
structures that are scattered
around among the
phospholipids.
Plasma Membrane
STRUCTURE
• This is a simple
representation of a
phospholipid.
• The yellow structure
represents the
hydrophilic or water
loving section.
• The blue tails that come
off of the sphere
represent the
hydrophobic or water
fearing end.
Plasma Membrane
FUNCTION
• Controls movement of
substances in & out of the
cell
• Forms a recognition site so
that the body’s immune
system can recognize its
own cells
• Acts as a receptor site for
the attachment of specific
hormones and
neurotransmitters.
Plasma Membrane
FUNCTION
• Not fixed – Proteins float
• Three categories
– Marker
– Receptor
– Transport
Membrane Proteins
MARKER PROTEINS
• Identify the cell
• The immune system uses these
proteins to tell friendly cells
from foreign invaders.
• They are as unique as
fingerprints. They play an
important role in organ
transplants.
• If the marker proteins on a
transplanted organ are different
from those of the original organ
the body will reject it as a
foreign invader
Membrane Proteins
RECEPTOR PROTEINS
• These proteins are used
in intercellular
communication.
• In this animation you can
see the a hormone
binding to the receptor.
This causes the
formation of a second
messenger
• The second messenger
acts as a signal molecule
releasing a signal to
perform some action.
Membrane Proteins
TRANSPORT PROTEINS
• Two Forms
• Carrier proteins are do not
extend all the way through
the membrane. They move
specific molecules through
the membrane one at a
time.
• Channel proteins extend
through the bi-lipid layer.
They form a pore through
the membrane that can
move molecules in several
ways.
How do molecules cross the
plasma membrane?
• Passive transport – movement that
requires no energy from the cell
• Active transport – movement that
requires energy from the cell
• Endocytosis and exocytosis – a special
type of active transport
CELLS
PASSIVE TRANSPORT
•
•
•
•
cell uses no energy
molecules move randomly
concentration is from high to low
three types
•SIMPLE DIFFUSION
•FACILITATED DIFFUSION
•OSMOSIS
Weeee!!
!
high
low
http://programs.northlandcollege.edu/biology/Biology1111/animations/transport1.html
Molecules are always moving
Molecules move randomly and bump into
each other and other barriers
• Diffusion occurs because the particles in
gases and liquids are moving.
DIFFUSION
• Particles in a liquid or gas
spread out…
• … from regions of high
concentration…
• … to regions of low
concentration…
• …until the particles are
evenly spread out.
Dissolving
KMnO4
crystal
• The difference between the regions of high
concentration and low concentration is called
the concentration gradient
High concentration gradient
Fast rate of diffusion
Low concentration gradient
Slow rate of diffusion
Concentration gradient
Concentration Gradient - change in the concentration of a
substance from one area to another.
Diffusion will continue until equilibrium is reached.
This means there will be an equal distribution of
molecules throughout the space. This is why food
coloring moves throughout a beaker of water; why odors
smell strong at first and then disappear over time.
Equilibrium, a result of diffusion, shows the uniform distribution of
molecules of different substances over time as indicated in the
above diagram.
WHAT AFFECTS DIFFUSION?
•
•
Movement of molecules from an area of high
concentration to an area of lower concentration.
Factors that affect the rate of diffusion: size of
molecules, size of pores in membrane,
temperature, pressure, and concentration.
Passive Transport:
Facilitated Diffusion
• Diffusion using transport proteins
found in the membrane
CHANNEL PROTEINS
• In some cases they act in passive
transport.
• Molecules diffuse randomly
through the opening, requiring
no energy, moving from an area
of high concentration to an area
of low concentration.
• Example: ion channel
SEMI-PERMEABLE MEMBRANES
A semi-permeable membrane will allow certain
molecules to pass through it, but not others.
Generally, small
particles can pass
through…
Partially permeable
membrane
…but large
particles
cannot
More free water molecules on this
side of membrane
Partially-permeable
membrane
Water-solute particle is too
large to pass through
membrane
Free water molecules diffuse in this direction
OSMOSIS
• Diffusion of water through a
selectively permeable
membrane
• Water moves from high to
low concentrations
• Water is so small and there is
so much of it the cell can’t
control its movement
through the cell membrane.
•Water moves freely
through pores.
•Solute (green) too large
to move across.
Hypotonic Solution
•
Osmosis
Animations for
isotonic,
hypertonic, and
hypotonic solutions
The solution has a lower concentration of solutes
and a higher concentration of water than inside the
cell. (Low solute; High water)
Result: Water moves from the solution to inside
the cell. The cell swells and bursts open (cytolysis)!
Hypertonic Solution
•
Osmosis
Animations for
isotonic,
hypertonic, and
hypotonic solutions
The solution has a higher concentration of solutes
and a lower concentration of water than inside the
cell. (High solute; Low water)
shrink
s
Result: Water moves from inside the cell into the
solution: Cell shrinks (Plasmolysis)!
Isotonic Solution
•
Osmosis
Animations for
isotonic,
hypertonic, and
hypotonic solutions
The concentration of solutes in the solution is
equal to the concentration of solutes inside the
cell.
Result: Water moves equally in both directions and
the cell remains same size! (Equilibrium)
What type of solution are these cells in?
A
Hypertonic
B
Isotonic
C
Hypotonic
How Organisms Deal
with Osmotic Pressure
•
Paramecium
(protist) removing
excess water video
•Bacteria and plants have cell walls that prevent them
from over-expanding. In plants the pressure exerted on
the cell wall is called tugor pressure.
•Protists like paramecium has contractile vacuoles that
collect water flowing in and pump it out to prevent them
from over-expanding.
•Salt water fish pump salt out of their specialized gills so
they do not dehydrate.
•Animal cells are bathed in blood. Kidneys keep the blood
isotonic by remove excess salt and water.
CELLS
•
•
•
•
ACTIVE TRANSPORT
Cell uses energy
Actively move molecules to where they are needed
Concentration is from low to high
This is
gonna
Three types
be hard
• PROTEIN PUMPS
work!!
high
• EXOCYTOSIS
• ENDOCYTOSIS
low
Active Transport
1. Protein Pumps
•Some transport proteins
actively use energy from
ATP in the cell to drag
molecules from area of low
concentration to areas of
high concentration (working
directly against diffusion)
•An example of this is the
sodium/potassium pump.
Here the energy of a
phosphate (shown in red) is
used to exchange sodium
atoms for potassium atoms.
Sodium
Potassium Pumps
(Active Transport
using proteins)
Protein changes shape
to move molecules: this
requires energy!
Active Transport
2. Endocytosis
• Taking large molecules
into a cell
•Uses energy
•Cell membrane in-folds
around food particle
•“cell eating”
•Forms food vacuole &
digests food
•This is how white blood
cells eat bacteria!
Active Transport
3. Exocytosis
•Forces large molecules out
of cell
• Membrane surrounding
the material fuses with
cell membrane
• Cell changes shape –
requires energy
• Hormones or wastes
released from cell
Endocytosis &
Exocytosis
animations