Cellular Transport

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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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Cellular Transport
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Cell is like a submarine

• Reasonably tough outer surface (membrane) that
  wraps around the complex machinery inside
• cell membrane separates what is inside cell from
  what is outside and is selectively permeable (
  some things can go through others can not)
• BUT, what about larger things that MUST get in
  and out?

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Cell Membrane

• Establish homeostasis (balance)
• phospholipid bilayer hydrophobic tails repel
  water
• hydrophilic heads attract water

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Types of proteins found in association with cell
membranes
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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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Fluid Mosaic Model of Cell Membranes

• The lipid bilayer behaves more like a liquid than
  a solid

• The lipids and proteins can move laterally within
  the lipid bilayer

• Example Pool with surface of water covered
  entirely with styrofoam peanuts

• any given peanut can move but not much due to
  surrounding peanuts

• remove enough peanuts to make room for a
  donut-shaped life preserver

• hole in the center of the preserver acts like a
  channel

http//www.stolaf.edu/people/giannini/flashanimat/
lipids/membrane20fluidity.swf
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Concentration and cells

• The concentration of a solution is the amount of
  solute per solvent
• Dilute more solvent per solute
• Concentrated more solute per solvent
• In a solution molecules are constantly moving and
  colliding, as a result they move from high
  concentration to low concentration (more crowded
  to less crowded)

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Concentration Gradient

• the difference in concentration across space
• molecules move with the "flow" across a
  concentration gradient looking for equilibrium
• molecules are constantly in motion and continue
  to move but stay evenly distributed

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Cellular Transport (How things move through
membranes)

• Passive transport requires no input of energy
  follows concentration gradient
• Ex. Diffusion ( concentration gradient flows
  from high to low concentration)
• Active transport DOES need energy to occur
  moves against the concentration gradient
  (concentration gradient flows from low to high)
• Ex. Pumps
• Ex. Endocytosis and Exocytosis

http//www.northland.cc.mn.us/biology/Biology1111/
animations/transport1.html
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Diffusion

• Movement of a substance from where there is a
  large amount of that substance to where there is
  a small amount of that substance
• (from an area of high concentration to an area of
  low concentration)
• Like a canoe in a stream go with the flow
• No energy needed
• 2 types dialysis and osmosis

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Figure 8.10 The diffusion of solutes across
membranes
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Osmosis

• Movement of WATER from an area of high water
  concentration to an area of low water
  concentration
• Ex. Flood of water into Titanic
• This type of diffusion is more common in cells
  because water molecules are smaller and easier to
  move than particles
• Water molecules can pass directly through the
  TINY spaces between phospholipid molecules and
  dont need to use channel proteins

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Terms that describe the conditions of mixtures
will only use these terms when are comparing
substances

• Hypertonic concentration of dissolved
  substances is higher than in what it is being
  compared to (more solute outside than inside)
• Hypotonic concentration of dissolved substances
  is lower than in what it is being compared to (
  more solute inside than outside)
• Isotonic concentration of dissolved substances
  is equivalent to the solution to which it is
  being compared to

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3 types of solutions
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The differences in concentration affect the
movement of water

• In Hypotonic the water moves into the cell to
  reach equilibrium causing the cell to swell
• In Hypertonic the water moves out of the cell to
  reach equilibrium causing the cell to shrink
• In Isotonic the water moves in and out equally so
  cell stays the same size

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Figure 8.12 The water balance of living cells
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Facilitated Diffusion

• Uses channels due to size of particles involved,
  but NO energy is requiredparticles are still
  moving from an area of high concentration to low
  concentration.

• Use carrier proteins that are specific for one
  type of molecule

- 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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Diffusion through Ion Channels

• Involves membrane proteins known as ion channels

• Ion channels- provide small passageways across
  the cell membrane

- Usually specific to one type of ion (such as
potassium, sodium, calcium, and chloride)
- Some are open all of the time, others have
gates that open when stimulated
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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