Download Ch. 3 Exchanging Materials with the Environment

Ch. 8 Exchanging Materials
with the Environment
Chapter Objectives:
1. Discuss the structure & function of
membranes in living organisms
2. Describe how materials are exchanged
across membranes
8-1 Cell Membrane
oWhat’s the purpose of the cell
membrane?
oAdds protection and support for a
cell
oCell Membrane – controls what
enters and leaves the cell
o Selectively Permeable
(Semi-Permeable)
oallows some materials into
the cell while keeping
other materials out
“Gate-keeper”
Useful in maintaining
Homeostasis:
• the tendency of an organism to maintain a
relatively stable internal environment by
regulating its metabolism & adjusting to its
environment.
• Other ways cell maintains homeostatsis
– Recognizes foreign material
– Communicates with other cells
What exactly needs to ENTER cells?
1. WATER – most chemicals require water as the
material to undergo a reaction within
2. OXYGEN (some cells do NOT take in this)
3. IONS = Na+, Mg+2, Ca+2, H+, Cl-, K+
4. CO2 (some cells do NOT take this in)
5. NUTRIENTS = sugars, amino acids, lipids
6. HORMONES
What exactly needs to LEAVE cells?
1. WASTES = Ammonium ion (NH+4),
CO2, O2, excess salts, excess H2O
etc . . .
2. Cell Products = Hormones & other
chemical products (ex: Proteins)
Membrane as a Barrier
• Membranes are composed of a Phospholipid
bilayer -2 layers of phospholipids & proteins
• SELECTIVELY PERMEABLE,
so NOT all substances are allowed
to pass
• Molecules that are SOLUBLE in the lipid
bilayer pass easily, (small, nonpolar
substances) but other molecules, like
charged Ions, and most polar molecules are
repelled by the nonpolar phospholipid tails
Hydrophobic vs. Hydrophilic
• “Water Fearing”
• Always NONPOLAR
• Repelled by water –
Insoluble in water
• Cannot make hydrogen
bonds with water
• These molecules tend to
cluster together in water,
forming droplets/bubbles
• Ex: Lipids, O2 gas . . .
• Hydrophilic = “Water
Loving”
• Typically POLAR
• Mostly soluble in water
• Capable of hydrogen
bonds with water
• Ex: Salts, Sugars . . .
A molecule’s permeability is determined by:
• 1. Size
• 2. Electric Charge
• 3. Polarity
• Transport Protein are embedded on the
membrane surface, help ions, amino acids
& sugars to enter the cell that can’t pass
through the lipid bilayer
Selectively permeable membrane
Fluid Mosaic Model
o“Fluid” –phospholipids and proteins are
able to move sideways
o“Mosaic” (a surface of small fragments) –
many different protein molecules with
various organic substances attached to them
Membrane Proteins
•1. Glycoproteins- Cell surface markers –
carbohydrate and protein, identify each cell
type
•2. receptor proteins- recognize and bind to
substances outside the cell
•3. Enzymes –assists chemical reactions inside
cell
•4. Transport Proteins – help substances move
across the cell membrane
Cell Membrane Components
Passage of Charged Molecules (Ions)
• Transport Protein are embedded on the membrane
surface, help ions across
• The Protein “gateways” also help amino acids & sugars to
enter the cell
• Large Proteins use different mechanism (explained later)
• Glycoproteins = specialized protein receptor on the cell
surface with an attached sugar
• Glycolipids = specialized lipid-sugar molecules in the cell
membrane – receives chemical messages from outside the
cell
Stop and Think
• 1.State the four roles (functions) of the cell
membrane.
• Structure support, recognizes foreign
material, communicates with other cells,
transports substances
• 2. Why can’t ions pass through the lipid
bilayer?
• They are repelled by the nonpolar interior of
the lipid bilayer
Ch. 8.2 Diffusion & Osmosis
• Diffusion = natural movement of molecules from an area
of high concentration to an area of low concentration
• This difference in the concentration over a distance is
called a Concentration Gradient
• The end goal of diffusion is to achieve Equilibrium
= when all molecules are equally spread apart (balance)
molecules are equally spread apart
– molecules still move,
but in equal #’s across
the membrane
Osmosis
oThe diffusion of water through a
selectively permeable membrane
o Water moves from areas of high to low
concentration.
o Concentration = mass of solute in a given volume
of soultion
oWater will move across the membrane
until the concentrations are equal on each
side
Osmosis – The Diffusion of H2O
• Parts of a solution:
• Solute = Dissolved substance
• Solvent = Substance doing the
dissolving (usually water)
• Solution = combination of solute + solvent
o In a solution…
oHigh water = Low solutes
oLow water = High solutes
Osmosis
•http://www.stjohn.ac.th/Department/school/bio_pix/osmosis.gif
Types of Solutions:
1) Isotonic
o Solutes and water are equal inside and
outside of the cell.
o No net movement of water - water moves in
and out of the cell in equal amounts, at
the same rate.
Types of Solutions:
2) Hypotonic
o Low solute concentration (High water)
outside of the cell.
o More water outside than inside the cell.
o Causes water to move into the cell.
Hypotonic Solutions cont’d
oWater entering the cell causes an increase in
turgor (osmotic) pressure on the membrane.
oPlants can withstand this increase because they
have cell walls.
oAnimal cells do not have cell walls, and they run
the risk of bursting – cytolysis.
oSome animal cells have special organelles –
contractile vacuoles – that pump access water
from their cells.
Types of Solutions:
3) Hypertonic
o High solute concentration (low water)
outside of the cell.
o More water inside the cell than outside the
cell.
o Causes water to move out of the cell.
Hypertonic Solutions cont’d
oPlasmolysis – the loss of water from a
cell
o Results in the drop of osmotic pressure
o In plant cells, the central vacuole shrinks,
loses support, and begins to wilt.
o http://www.youtube.com/watch?v=gWkcFUhHUk&feature=PlayList&p=597DCBAA391B9074&playnext=1&pla
ynext_from=PL&index=29
o http://www.youtube.com/watch?v=H6N1IiJTmnc&feature=fvw
o Animal cells can eventually shrink and die.
Hypo-, Iso-, & Hypertonic
Hypotonic =
“below strength”
Hypotonic
Isotonic = “same
strength”
Hypertonic =
“above strength”
Isotonic
Hypertonic
Plasmolysis!
Review Questions
Label the following solutions as isotonic, hypertonic, or hypotonic.
1. A cell with 97% water is placed into an environment with 100% water.
A. Hypotonic
2. A cell shrinks and becomes weak.
A. Hypertonic
3. A plant cell develops turgor pressure.
A. Hypotonic
4. A fresh water cell (97% water) lives in a pond that is 97% water.
A. Isotonic
5. A fresh water cell (97% water) is placed into the ocean (88% water.)
A. Hypertonic
6. An animal cell bursts.
A. Hypotonic
8.2 Means of Transport
• 1.) Passive Transport
Is diffusion without any input of energy
2.) Active Transport
Moves substances against their concentration
gradients and thus requires energy
Passive vs. Active Transport
• Diffusion
• Requires (ATP)
WITHOUT (ATP)
• Moves molecules
• Moves molecules
AGAINST the
DOWN/WITH the
concentration
concentration
gradient (low-> high)
gradient (high->low) • Ex: Endocytosis,
• Ex: Simple diffusion,
Exocytosis &
Facilitated diffusion
Sodium-Potassium
& Osmosis
Pump
Facilitated Diffusion
• A form of Passive transport
• Uses transport proteins in cell membrane to move molecules
– Either through an open channel or carry specific molecules across
• Molecules move with the concentration gradient, therefore
do not need ATP
• Makes transport more specific & speeds up rate
Facilitated Diffusion cont.
• Carrier Proteins- transport substances that
fit in their binding site
– Binding causes protein to change shape
– Change moves substance across membrane
• Channel proteins- tunnels through lipid
bilayer
– Allows diffusion o f specific substances with
right size and shape
Endocytosis vs. Exocytosis
• Active transport of
substances INTO cell
• Useful way for unicellular
organisms to acquire food
• Cell literally surrounds
particle with its cell
membrane & engulfs the
particle into itself
• Active transport of
substances OUT of cell
• Mostly for waste removal &
export of enzymes or
hormones
• Vesicles carrying substances
fuse with inside of cell
membrane & open up to
external environment,
releasing material
Sodium-Potassium Pump
• Type of active transport
• Requires energy (ATP) to “pump” substances
across membrane
• Uses carrier proteins
• Prevents sodium (Na+) from building up in cell
– Cells would swell or burst if too much water enters
through osmosis
Sodium-Potassium pump steps
• 3 Na+ ions bind to pump
• Phosphate from ATP also binds to give energy
• Pump changes shape and releases 3 Na+ ions to
outside of cell
• 2 K+ ions bind to pump and cross membrane
• Phosphate group released, pump returns to original
shape
• K+ is released into the cell
Sodium-Potassium Pump
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html
• Na/K Pump = an enzyme protein that moves 3 sodium
ions out of a cell while moving 2 potassium ions in.
• Prime example of how electrolytes are critical to health
• Essential to muscle contraction & nervous system
conduction
THE END
What types of molecules can cross the lipid
bilayer?
• Can Cross
– Small hydrophobic
molecules
like gases
– Small uncharged polar
molecules like water
(small hydrophilic
molecules)
• Can’t Cross
– Larger uncharged polar
molecules like amino
acids, glucose and
nucleotides
– Ions or charged
molecules like H+
Cellular Energy
• Cells use a form of chemical energy called
Adenosine Triphosphate (ATP)
• Cells store & use ATP to fuel necessary
metabolic reactions
– Such as maintaining internal chemical
conditions (homeostasis)
• 10 MILLION molecules of ATP are
consumed & regenerated per second per
cell!
Adenosine Triphosphate (ATP)
Nucleotide
Sugar
3 Energy Rich
Phosphate Bonds
ATP – ADP Cycle:
Materials that Pass & Do Not Pass
Passage of Charged Molecules (Ions)
• Transport Protein are embedded on the membrane
surface, help ions across
• The Protein “gateways” also help amino acids & sugars to
enter the cell
• Large Proteins use different mechanism (explained later)
• Glycoproteins = specialized protein receptor on the cell
surface with an attached sugar
• Glycolipids = specialized lipid-sugar molecules in the cell
membrane – receives chemical messages from outside the
cell
Diffusion, cont . . .
• Due to this natural movement, substances diffuse across
cell membranes without the need for metabolic energy
(ATP) to be spent by
the cell
• At equilibrium,
molecules still move,
but now they move in
equal #’s across the
membrane
• Rate of diffusion depends
on: size of concentration
gradient, surface area
• of membrane &
• temperature.
Ch. 2.8 Energy Transfer & ATP
• Decomposition rnxs release free energy thru a
process called OXIDATION
• Oxidation is the removal of electrons from a
molecule & then certain bonds are broken &
rearranged
• Energy is then released as free energy & heat
• The free energy ultimately ends up in a molecule
called ATP  Adenosine Triphosphate
• ATP is the “energy currency” your cells “spend” for
all metabolic reactions
ATP  ADP
• The way free energy is released from ATP is when
the chemical bond between the 2nd & 3rd phosphate
groups is broken:
• ATP now becomes ADP (Adenosine Diphosphate)