3 types of proteins found associated with cell membrane

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3 types of proteins found associated with cell
membrane

• Channel Proteins form physical pathway through
  phospholipid bilayer
• Receptor Proteins change shape as other
  molecules bind to them and pass INFO into the
  cell (nothing physically passes through)
• Marker Proteins identify the specific type of
  cell (so when organism needs to repair/replace
  cells, can do so with correct type)

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Homeostasis and Cellular Transport
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What is Homeostasis?
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A. The stable internal conditions of a living
thing
B. Balanced and controlled conditions in the
internal environment of an organism
C. Maintained by both voluntary and involuntary
responses
1. Voluntary
a. Drinking water when thirsty
b. Adding clothes when cold
2. Involuntary
a. Shivering when cold
b. Developing goose bumps
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D. Disease/illness sets in when homeostasis cant
be achieved
1. Example When a fever develops due to the
flu
E. Some internal systems that maintain homeostasis
1. Waste removal
2. pH levels
3. Glucose levels- too low and your brain can
cease functioning
4. Ion balance-without this balance the heart
wont function
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5. Blood O2 and CO2 levels-cells will die
without O2 too much CO2 changes pH
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What is Passive Transport?
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A. The movement of substances across the cell
membrane B. 4 types of Passive Transport 1.
Diffusion 2. Osmosis 3. Facilitated diffusion
4. Diffusion through ion channels
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What is Diffusion?
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C. Movement of molecules from area of higher
concentration to area of lower
concentration 1. Two types dialysis and
osmosis a. Dialysis-movement of particles
("stuff") over time and distance i.
spray perfume in corner of the room,
eventually it disperses b. Osmosis-movement of
water (see additional notes below)
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Figure 8.10 The diffusion of solutes across
membranes
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What is a Concentration Gradient?
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D. Molecules move with the "flow" across a
concentration gradient looking for
equilibrium 1. Concentration gradient-the
difference in concentration across
space a. example a sugar cube dissolving in a
glass of water-sugar molecules spread
out 2. Driven by kinetic energy (the energy of
motion) a. Molecules are constantly in
motion b. Move in a straight line until they
hit something and bounce off in another
direction (like pinball or pool)
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c. Because of this, molecules move down the
concentration gradient from areas of high
conc. to areas of low conc. 3. Will continue
until they reach equilibrium a. Become evenly
distributed across space. b. Still continue to
move but stay evenly distributed 4. Remember-t
he cell membrane is selectively
permeable a. Allows some molecules to pass
through but not others (white picket fence)
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b. So...molecules will move through the
membrane by diffusion c. The ability of
molecules to diffuse across a membrane depends
on 3 things i. the size of the
molecules ii. the shape of the
molecules iii. the chemical nature of the
membrane d. Molecules that can be dissolved in
lipids can pass through the cell membrane (see
facilitated diffusion
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What is Osmosis?
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E. Movement of water from high to low
concentration 1. Since the particles can't
move the water does! 2. The direction of this
movement depends on the concentration of
solutes on the two sides of the cell membrane
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What is a Hypotonic Solution?
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a. Hypotonic-term used when a solution has
less "stuff" (solute) and more water
(solvent) when compared to another
solution i. water enters (diffuses into)
the cell until equilibrium is
achieved ii. causes swelling and the
possiblity of cytolysis bursting of cells
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What is a Hypertonic Solution?
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b. Hypertonic-term used when a solution has
more "stuff" (solute) and less water
(solvent) when compared to another
solution i. water leaves (diffuses out of)
the cell until equilibrium is
achieved ii. causes shrinking/shriveling
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What is an Isotonic Solution?
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c. Isotonic-term used when solutions have the
same amount of "stuff (solute) and water
(solvent) i. even exchange (of water and
dissolved solids) from within and outside
the cell ii. cells that exist in this env.
maintain homeostasis rather easily
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3 types of solutions
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Figure 8.12 The water balance of living cells
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What is Facilitated Diffusion?
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F. Used for molecules that cannot diffuse across
the cell membrane 1. Not soluble in
lipids 2. Too large to pass through
pores 3. Use carrier proteins that are specific
for one type of molecule a. Carrier
proteins-a protein that transports specific
substances across a biological membrane (hence
the name carrier)
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Figure 8.14 Two models for facilitated diffusion
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What is Diffusion through Ion Channels?
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G. Involves membrane proteins known as ion
channels 1. Ion channels-provide small
passageways across the cell membrane a. Usual
ly specific to one type of ion i. ions such
as potassium, sodium, calcium, and chloride
are not soluble in lipids b. Some are open
all of the time, others have gates that open
when stimulated
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c. Necessary because ions cannot diffuse
across the membrane without these
passageways
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What is Active Transport?
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A. The movement of molecules up their
concentration gradient (lower conc. to higher
conc.)-requires energy from the cell
1. Membrane pumps- special carrier proteins that
move substances up their conc. gradients.
a. The carrier proteins in the pumps
i. bind to a molecule on one side of the
membrane
ii. changes shape shielding the molecule
from the hydrophobic interior of the lipid
bilayer
iii. transports it across the membrane
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b. Example Sodium-Potassium Pump
i. transports Na and K ions across the
lipid bilayer
ii. many animals must have higher conc. of
Na outside the cell and K inside the
cell
iii. moves 3 Na out of cell and 2 K inside
the cell
iv. requires ATP to fuel transport
2. Some substances are too large to pass
through the cell membrane using these
processes-must use endocytosis or exocytosis
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a. Endocytosis-ingest external fluid,
macromolecules, and large particles
i. outside of the cell collects material and
wraps itself around it creating a pouch
called a vesicle
ii. the vesicle pinches off the cell membrane
and attaches to a lysosome or other
membrane-bound organelle
iii. 2 types of endocytosis pinocytosis
phagocytosis
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pinocytosis (cell drinker)- brings in
liquids
phagocytosis (cell eater)- brings in
solids that are too big for channel proteins
iv. phagocytes ingest bacteria and viruses and
with the help of lysosomal enzymes, are
destroyed
b. Exocytosis- release contents outside the cell
i. vesicles form inside the cell and fuse to
the cell membrane
ii. used to release large molecules such as
proteins to the cells surface