a8) transport across the membrane
TRANSCRIPT
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PRESCRIBED LEARNING OUTCOMES(Chapter 4, pp. 65-76)
G1. Apply knowledge of organic molecules to explain the structure and
function of the fluid-mosaic model
G2. Explain why the cell membrane is described as selectively
permeable
G3. Compare and contrast the following: diffusion, facilitated transport,
osmosis, and active transport.
G4. Explain factors that affect the rate of diffusion across a cell
membrane.
G5. Describe endocytosis, including phagocytosis and pinocytosis, and
contrast it with exocytosis.
G6. Predict the effects of hypertonic, isotonic, and hypotonic
environments on animal cells
G7. Demonstrate an understanding of the relationship and significance
of surface area to volume, with reference to cell size.
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_____ Active transport
_____ ATP energy
_____ Blood antigen
_____ Concentration gradient
_____ Crenate
_____ Diffusion_____ Endocytosis
_____ Exocytosis
_____ Facilitated transport
_____ Glycolipid
_____ Glycoprotein
_____ Hemolysis_____ Hypertonic
_____ Hypotonic
_____ Isotonic
_____ Na/K pump
_____ Neuron
_____ Osmosis
_____ Osmotic pressure
_____ Phagocytosis
_____ Phospholipid
_____ Pinocytosis
_____ Polarity
_____ Protein channels
_____ Receptor sites
_____ Selectively permeable
_____ Solubility
_____ Solute
_____ Solvent
_____ Surface area/volume ratio_____ Thyroid gland
_____ Thyroxin
_____ Tonicity
_____ Turgor pressure
_____ Villi
_____ Viscosity
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SELECTIVELY PERMEABLE: Controls what comes in and outof the cell. Does not letlarge, chargedor polarthings through
without help.
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FLUID MOSAIC MODEL: The phospholipids move, thus
allowing small non-polar molecules to slip through.
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GLYCOLIPIDS and GLYCOPROTEINS: Act as
receptorsreceive info. from body to tell cell
what to do.
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INTEGRAL PROTEINS: assistsspecific larger and charged
molecules to move in and outof the cell. Can act as tunnels
or will change shape.
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CHOLESTEROL: Reducesmembrane fluidityby reducingphospholipid movement. Also stops the membrane from
becoming solidat room temperatures.
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CYTOSKELETON: A cytoskeleton acts as a framework thatgives the cell it's shape. It also serves as a monorail to
transportorganelles around the cell.
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1. Passive transportmoves
molecules from a [high]to[low]in order to establish
equilibrium.
The molecules may or maynot need to use aprotein
channel or carrier.
Everything that is transported across the cell membranetakes place by one of two fundamental processes:
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2. Active transportmoves molecules from [low]to [high],
AGAINSTthe concentration gradient and this process
requiresenergyin the form of ATP.
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Simple Diffusionis a passiveprocess ( noenergy required).
Some substances will diffuse through
membranes as if the membranes
werent even there.
Molecules diffuse until they are
evenlydistributed.
The molecules move from an area of [high] to [low].
EXAMPLES of moleculesthat easily cross cell membranes
by simple diffusion are: oxygen, carbon dio xide, alcoho ls,
fatty acids, gly cerol, and urea.
http://www.schoolscience.co.uk/content/3/chemistry/materials/images/diffusion3.gif -
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Alcohol Urea
Fatty Acids, Glycerol,
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The rate of diffusion will be increased when there is :
1. Concen trat ion: the difference in [ ] between two areas
(the [ ] gradient) causes diffusion. The greater the
difference in concentration,the fasterthe diffusion.
2. Mo lecu lar s ize: smaller substances diffuse more quickly.
Large molecules (such as starches and proteins) simply
cannot diffuse through.
3. Shape of Ion /Molecule: a substances shape may prevent
it from diffusing rapidly, where others may have a shape
that aids their diffusion.
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4. Visco sity o f the Medium: the lower the viscosity, the moreslowlymolecules can move through it.
5. Movement of the Medium: currents will aid diffusion. Like
the wind in air, cytop lasm ic steaming(constant movement
of the cytoplasm) will aid diffusion in the cell.
6. So lu bi l i ty : lipid- soluble molecules will dissolve through
the phospholipid bilayer easily,as will gases like CO2and
O2.
7. Polarity: waterwill diffuse, but because of its polarity, it will
notpass through the non-polar phospholipids. Instead,
water passes though specialized protein ionchannels.
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Osmosisis the diffusionof wateracross a selectively
permeable membranedriven by a difference in the
concentration of soluteson the two sides of the membrane.
A selectively permeable
membrane is one that
allows unrestricted
passage of water, but not
solute molecules or ions.
So it is the WATER THAT
MOVESto create
equilibrium!!!
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Osmosis requires NOENERGY.
Osmosis is the net movement of
WATERmolecules from the area
of [high]of water to the area of
[low]of water until it is equally
distributed.
Because membranes often
restrict or preventthe movementof some molecules, particularly
large ones, the water (solvent)
must be the one to move.
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To cross the membrane,
water must move througha protein ion channel.
In certain cellular
conditions, these protein
channels can be opened
or closed (ie: in the
kidneys, large
intestines) depending on
how much water isneeded by the body.
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ISOTONIC SOLUTION:
1. the solution concentration is
equalon both s ides of themembrane.
2. There is no net concentration
difference across the cell
membrane
3. Water moves back and forth,
but there is no net gain or
lossof water.
The ton ic i ty o f a solut ion w il l affect the size & shape of cel ls:
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HYPERTONIC SOLUTION:
1. The solution outsidethe cell
is more concentrated than
inside.
2. There is more water inside
the cell and the water will
move outof the cell.
3. This causes the cell toshrink
4. *Memory Trick... Hyper
people get skinny!
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HYPOTONIC SOLUTION:1. The concentration insidethe
cell is more concentrated than
outside.
2. Therefore there is more wateroutside of the cell, and water
will move intothe cell.
3. This will cause the cell toswell.
4. *Memory Trick...Hippos are
FAT!
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In Biology we usually talk about the SOLUTIONS tonicity,
NOT the cells!
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*MEMORY TRICK: If you eat a lot of sugar (ie: solute)
you get HYPER. The solution with a lot of solute is
called HYPEROSMOTIC.
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When we speak of plants, we speak of TURGOR PRESSURE.
Which of these cells is in a hypertonic solution? Hypotonic?
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Facilitated Transport: Some molecules are not
normally able to pass through the lipid membrane,
and need channel or carrierproteinsto help
them move across.
This does notrequire energywhen moving
from [H] to [L] (with the concentration gradient).
Molecules that need help to move through theplasma membrane are either charged, polar,
or too large.
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Each protein
channel or protein
carrier will allowonly ONE TYPE
OF MOLECULEto
pass through it.
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Many channels contain a gatewhich control the channel's
permeability.
When the gate is open, the channel transports, and when thegate is closed, the channel is closed.
These gates are extremely important in the nervecells.
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Active Transport: the movement of
polar, large, and charged molecules
moving againstthe [ ] gradient
(uphill).
EXAMPLES of moleculesthat
move this way are all of the things
that require protein carriers to move
across the plasma membrane.
ions(like Na+ and K+ in cells, and
iodine) and sugars, amino acids,
nucleotides...
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Example 2: a Na/K pump (mostly in nerve membranes).These function to restore electrical order in a nerve after an
impulse has traveled along it.
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Example 3: In order to make ATP in the mitochondria, aproton pump (hydrogen ion) is required.
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Endocytosis: (Endo means in).
Endocytosis is the taking in of molecules or particles by
invaginationof the cell membrane forming a vesicle.
This requires energy.
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There are two types of endocytosis:
1. pinocytosis(cell drinking): small
molecules are ingested and a vesicle is
immediately formed. This is seen in
small intestinecells (villi)
2. phagocytosis(cell eating): large
particles, (visible with light microscope)
are invaginated into the cell (ie: white
blood cells eat bacteria).
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Exocytosis: (Exo means out.)
Exocytosis is the reverseof
endocytosis.
This is where a cell releases the
contentsof a vesicle outside of the cell.
These contents may be wastes, proteins, hormones, or
some other product for secretion.
This also requires energy.
Example: vesicles from the Golgifuse with the plasma
membrane and the proteins are released outside of the cell.
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Cells exist individually, or in groups
forming tissues, organs, and
eventually organisms.
Their sizeis a very important
factor for their survival.
Cells are the size they are because
that is the size they have to be
in order to functioneffectively.The materials it needs to use, and the wastesit needs to
remove must pass in and out of the cell through the cell
membrane.
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As a cell grows, it suffers the possibility of the volume
increasing fasterthan the surface area.
The bigger the cell, the more it needsand the more it needs
to get rid of.
If the cell gets too big, there will not be enough roomon the
plasma membranefor things to get in and out quickly
enough to maintain the cell.
Why? Its surface area has not kept up to its volume size.
When the volume of a cell increases, the amount of surface
area does not increase in the same proportion.
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When cells grow larger,if they dont want to
die, the only real
solution is to divide.
Once a cell has divided,
the surface area to
volume ratio will
increaseand the
problem is solved.
*When you see questions regarding surface area to
volume ratio think of a water balloon
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volume ratio, think of a water balloon.
(ie: when you squish a water balloon, it has the same
volume, but the surface area is increased!)