Ch. 8 Exchanging Materials Ch. 8 Exchanging Materials with the Environmentwith 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 MembraneoWhat’s the purpose of the cell membrane?oAdds protection and support for a celloCell 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 maintainingHomeostasis:

• the tendency of an organism to maintain a the tendency of an organism to maintain a relatively stable internal environment by relatively stable internal environment by regulating its metabolism & adjusting to its regulating its metabolism & adjusting to its environmentenvironment..

• Other ways cell maintains homeostatsisOther ways cell maintains homeostatsis– Recognizes foreign materialRecognizes foreign material– Communicates with other cellsCommunicates with other cells

What exactly needs to What exactly needs to ENTERENTER cells? 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 What exactly needs to LEAVELEAVE cells? 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 BarrierMembrane 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 sidewayso“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 ComponentsCell Membrane Components

Passage of Charged Molecules (Ions)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 + solvento In a solution…

oHigh water = Low solutesoLow 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 pressureo In plant cells, the central vacuole

shrinks, loses support, and begins to wilt.

o http://www.youtube.com/watch?v=gWkcFU-hHUk&feature=PlayList&p=597DCBAA391B9074&playnext=1&playnext_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

Isotonic

Hypertonic

Hypotonic = “below strength”

Isotonic = “same strength”

Hypertonic = “above strength”

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. Hypotonic2.A cell shrinks and becomes weak.

A. Hypertonic3.A plant cell develops turgor pressure.

A. Hypotonic4.A fresh water cell (97% water) lives in a pond that is 97% water.

A. Isotonic5.A fresh water cell (97% water) is placed into the ocean (88% water.)

A. Hypertonic6.An animal cell bursts.

A. Hypotonic 

8.2 Means of Transport

• 1.) Passive TransportIs diffusion without any input of energy

2.) Active Transport

Moves substances against their concentration gradients and thus requires energy

Passive vs. Active Transport• Diffusion

WITHOUT (ATP)

• Moves molecules DOWN/WITH the concentration gradient (high->low)

• Ex: Simple diffusion, Facilitated diffusion & Osmosis

• Requires (ATP)

• Moves molecules AGAINST the concentration gradient (low-> high)

• Ex: Endocytosis, Exocytosis & Sodium-Potassium 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

• 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

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html

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 PassMaterials that Pass & Do Not Pass

Passage of Charged Molecules (Ions)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)