Cell Structure and FunctionCell Structure and Function

Chapter 7Chapter 7

Cell HistoryCell History

• Robert Hooke (1635-Robert Hooke (1635-1703)1703)

• Viewed slices of cork Viewed slices of cork under a crude under a crude compound microscopecompound microscope

• He saw boxes which He saw boxes which reminded him of cells reminded him of cells that monks lived inthat monks lived in– Hence the name “cell”Hence the name “cell”

Hooke’s MicroscopeHooke’s Microscope

Cell HistoryCell History

• Anton van Leeuwenhoek Anton van Leeuwenhoek (1632-1723)(1632-1723)

• Designed an early Designed an early microscopemicroscope

• First to see living First to see living organisms in a drop of organisms in a drop of waterwater

Cell HistoryCell History

• Robert Brown (1773-1858)Robert Brown (1773-1858)

• Used special stains and dye Used special stains and dye to view nucleusto view nucleus

Cell HistoryCell History

Mathias Schleiden, Mathias Schleiden, botanist (1804-1881)botanist (1804-1881)

Theodor Schwann, Theodor Schwann, zoologist, (1810-1882)zoologist, (1810-1882)

Rudolph Virchow, Rudolph Virchow, physician (1821-1902)physician (1821-1902)

Cell TheoryCell Theory

• Schleiden, Schwann and Virchow Schleiden, Schwann and Virchow each contributed to the cell theory each contributed to the cell theory (1838-9):(1838-9):

1.1. Cells are the basic unit of structure Cells are the basic unit of structure and function of all living thingsand function of all living things

2.2. All living things are composed of one All living things are composed of one or more cellsor more cells

3.3. New cells are produced from existing New cells are produced from existing cellscells

Cell TypesCell Types

• ProkaryoticProkaryotic– First appear in fossil First appear in fossil

record 3.5 BYArecord 3.5 BYA– No membrane bound No membrane bound

organellesorganelles– BacteriaBacteria

• EukaryoticEukaryotic– Evolved 1.5 BYAEvolved 1.5 BYA– Have membrane Have membrane

bound organellesbound organelles– Protists, fungi, Protists, fungi,

animals, plantsanimals, plants

Cell StructuresCell Structures

• Cell WallCell Wall– Found in plants, Found in plants,

fungi, algae, and fungi, algae, and most bacteriamost bacteria

– RigidRigid– Provide structure Provide structure

and protectionand protection– Composed of Composed of

cellulose or chitincellulose or chitin

Cell StructuresCell Structures

• Cell MembraneCell Membrane– Selectively permeable Selectively permeable

• Regulates what goes in Regulates what goes in and outand out

– FlexibleFlexible– Provides protection Provides protection

and supportand support– Made of a lipid bilayerMade of a lipid bilayer

Cell MembraneCell Membrane

• Regulates what goes in and out of the Regulates what goes in and out of the cell – SELECTIVE PERMEABILITYcell – SELECTIVE PERMEABILITY

• Wastes and cell products need to exitWastes and cell products need to exit– COCO22, O, O22 (in plants), hormones (in plants), hormones

• Nutrients need to enterNutrients need to enter– Sugar, OSugar, O22, CO, CO22 (in plants), amino acids (in plants), amino acids

• Lipid BilayerLipid Bilayer

PhospholipidsPhospholipids

• Fatty acid tails are Fatty acid tails are non-polarnon-polar

• Heads are polarHeads are polar• Tails don’t want to Tails don’t want to

be near water be near water because water is because water is polarpolar

• Polar Polar ♥ Polar♥ Polar• Non-polar ≠ PolarNon-polar ≠ Polar

Cell MembraneCell Membrane

• Fluid Mosaic ModelFluid Mosaic Model– Fluid: in motionFluid: in motion -Mosaic: different stuff-Mosaic: different stuff

Outsideof cell

Insideof cell(cytoplasm)

Cellmembrane

Proteins

Proteinchannel

Lipid bilayer

Carbohydratechains

http://telstar.ote.cmu.edu/Hughes/tutorial/cellmembranes/bil.swf

Cell TransportCell Transport

• Substances need to cross the CMSubstances need to cross the CM

• Some molecules are small and non-Some molecules are small and non-polar polar → don’t require energy→ don’t require energy– OO22, CO, CO22

• Some molecules are polar or too big to Some molecules are polar or too big to cross CM → do require energycross CM → do require energy– Proteins, sugarsProteins, sugars

DiffusionDiffusion

• Movement of molecules from an area of Movement of molecules from an area of high concentration to low high concentration to low concentrationconcentration

• http://www.biosci.ohiou.edu/introbioslahttp://www.biosci.ohiou.edu/introbioslab/Bios170/diffusion/Diffusion.htmlb/Bios170/diffusion/Diffusion.html

• Small, non-polar molecules will diffuse Small, non-polar molecules will diffuse across CMacross CM

• DOES NOT REQUIRE ENERGY!! = DOES NOT REQUIRE ENERGY!! = Passive TransportPassive Transport

Dynamic EquilibriumDynamic Equilibrium

• Dynamic = changing, movingDynamic = changing, moving

• Equilibrium = balancedEquilibrium = balanced

• Molecules will diffuse until dynamic Molecules will diffuse until dynamic equilibrium is reachedequilibrium is reached

• Molecules will continue to moveMolecules will continue to move

OsmosisOsmosis

• Diffusion of water across a membraneDiffusion of water across a membrane

OsmosisOsmosis

• High water to low waterHigh water to low water

• Fresh water to salt waterFresh water to salt water

• http://www.stolaf.edu/people/giannini/flhttp://www.stolaf.edu/people/giannini/flashanimat/transport/osmosis.swfashanimat/transport/osmosis.swf

Hypotonic SolutionHypotonic Solution

• ‘‘Hypo-’ means lessHypo-’ means less• Concentration of Concentration of

solute (dissolved solute (dissolved solids) is solids) is lessless outside of cell than outside of cell than insideinside

• Water will enter cellWater will enter cell• Cell may lyse (burst)Cell may lyse (burst)• Cell wall prevents Cell wall prevents

lysis in plant cellslysis in plant cells

Hypertonic SolutionHypertonic Solution

• ‘‘Hyper-’ means Hyper-’ means moremore

• Concentration of Concentration of solute is solute is higher higher outside of celloutside of cell

• Cell will lose waterCell will lose water• Plasmolysis results Plasmolysis results

in plant cellsin plant cells

Isotonic SolutionIsotonic Solution

• ‘‘Iso-’ means equalIso-’ means equal• Solute concentration Solute concentration

is the is the samesame outside outside and inside the celland inside the cell

• No change in cell sizeNo change in cell size• Animals prefer thisAnimals prefer this

Facilitated DiffusionFacilitated Diffusion

• Large molecules moving down their Large molecules moving down their concentration gradient use a protein to concentration gradient use a protein to facilitate (help) their crossing the CMfacilitate (help) their crossing the CM

• Diffusion = no energy!Diffusion = no energy!

Facilitated DiffusionFacilitated Diffusion

Active TransportActive Transport

• Requires energyRequires energy

• Used for large molecules or substances Used for large molecules or substances moving against their concentration moving against their concentration gradient (low to high)gradient (low to high)

• Exocytosis – exiting cellExocytosis – exiting cell

• Endocytosis – entering cellEndocytosis – entering cell

Active TransportActive Transport

Endo- and ExocytosisEndo- and Exocytosis

Levels of Levels of OrganizationOrganization