Download Cell Membrane and Transport Powerpoint

Cell Membrane
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The composition of nearly all cell membranes
is a double-layered sheet called a lipid
bilayer. The phospholipid bilayer gives cell
membranes a flexible structure that forms a
strong barrier between the cell and its
surroundings. The cell membrane
regulates what enters and leaves the
cell and also provides the cell with
protection and support.
Structure of Cell Membrane
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Has a phospholipid bilayer (2 layers of
fat).
The Cell Membrane
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Maintains homeostasis for the cell by
allowing waste and other products to
leave the cell.
Selectively Permeable – allows only
some materials in and out of the cell.
Water and oxygen move freely across
the cell's membrane.
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The phospholipids have a:
– hydrophilic head (water loving)
– two hydrophobic tails (water fearing)
Cell Membrane
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The Cell Membrane is also called
“The Fluid Mosaic Model”
– Because the membrane is flexible and the
lipids move within the membrane. (like
water molecules move in the currents of
a lake).
– Also because proteins create a “mosaic”
or pattern on the surface of the
membrane.
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Another type of lipid in the cell membrane is
CHOLESTEROL that makes the membrane more
fluid.
Embedded in the phospholipid bilayer are PROTEINS
that also aid in diffusion and in cell recognition.
Proteins called INTEGRAL proteins go all the way
through the bilayer, while PERIPHERAL proteins are
only on one side.
Large molecules like PROTEINS or carbohydrates use
proteins to help move across cell membranes.
Some of the membrane proteins have carbohydrate
chains attached to help cells in recognize each other
and certain molecules
Passive Transportmoving molecules across
cell membrane
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Does NOT require energy.
Three Types:
– Diffusion
– Osmosis
– Facilitated Diffusion
Diffusion
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As a result, the particles tend to move
from an area of greater concentration
to an area of lower concentration.
EQUILIBRIUM- when the molecules are even
throughout a space.
Diffusion depends upon random
particle movements, across membranes
without requiring extra energy
http://www.youtube.com/watch?v=E7kor5nHtZQ&feature=endscreen&NR=1
Facilitated Diffusion
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Movement of large molecules across the cell
membrane using PROTEINS!!
Cell membranes have transport proteins
that act as carriers, making it easy for certain
molecules to cross.
Each channel is specific for 1 type of
molecule
facilitating, or helping, the diffusion of
molecules across the membrane, and this is
called facilitated diffusion.
Osmosis
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The movement of WATER across the cell
membrane from high concentration to low
concentration.
Huddle Up
1.
What part of the cell membrane is
hydrophilic? What part is hydrophobic?
2.
What is diffusion?
3.
What is osmosis?
Three Types of Solutions
 Isotonic
 Hypotonic
 Hypertonic
– Recall a Solution = Solute + Solvent
– Solute – substance being dissolved
– -Solvent – substance that does the
dissolving
Isotonic Solution“ISO” means same
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If the concentration of solute (salt)
is equal on both sides, the water
will move back and forth equally.
Hypotonic Solution“HYPO” means less
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There are less solute (salt) molecules in the
solution so water will move into the cell.
Cell gets larger and could burst and die.
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.
http://www.youtube.com
/watch?v=N8hAwVaaD84
Hypertonic Solution“Hyper” means more
There are more solute (salt) molecules
in the solution, so the water is sucked
out of the cell.
 Cell shrinks,
causes cell to die.
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Osmotic Pressure
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For organisms to survive, they
must have a way to balance the
intake and loss of water.
Can Drinking Salt Water
Hurt You?
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Yes! This is why it is dangerous to drink
sea water.
Its a myth that drinking sea water will cause
you to go insane, but people marooned at
sea will speed up dehydration (and death)
by drinking sea water.
This is also why "salting fields" was a
common tactic during war. It would kill the
crops in the field, thus causing food
shortages.
Active Transport
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REQUIRES ENERGY b/c materials
are moving against the concentration
gradient.
Molecules from an area of LOW
concentration to HIGH
concentration.
Active Transport
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The active transport of small molecules or
ions across a cell membrane is generally
carried out by transport proteins or
“pumps” that are found in the membrane
itself.
Larger molecules and clumps of material can
also be actively transported across the cell
membrane by processes known as
endocytosis and exocytosis.
Types of Active Transport
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Endocytosis- moving large particles
INTO the cell by the cell membrane
engulfing them.
– Phagocytosis: engulf large FOOD
particles
– Pinocytosis: engulf large LIQUID
particles
Exocytosis – moving large particles
OUT of the cell.
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Endocytosis (en-doh-sy-TOH-sis) is
the process of taking material into the
cell by means of infoldings, or pockets,
of the cell membrane.
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Phagocytosis means “cell eating.” In
phagocytosis, extensions of cytoplasm
surround a particle and package it
within a food vacuole. The cell then
engulfs and digests it.
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Exocytosis (ek-soh-sy-TOH-sis) is the
process by which cells release large
amounts of material from the cell.