Chapter 5Chapter 5

Homeostasis & Homeostasis &

The Plasma MembraneThe Plasma Membrane

The Plasma MembraneThe Plasma Membrane

It’s all about balance!It’s all about balance!

Failure to adjust….deathFailure to adjust….death

Cells maintain balance by controlling Cells maintain balance by controlling materials entering/leavingmaterials entering/leaving

Concentrations outside the cell changeConcentrations outside the cell change

Plasma membrane must be able to Plasma membrane must be able to maintain balancemaintain balance

Selective PermeabilitySelective Permeability-property that -property that allows some materials to pass through allows some materials to pass through while keeping others outwhile keeping others out

Membrane StructureMembrane Structure

Made of two layers made up of sheets of Made of two layers made up of sheets of lipid molecules-lipid molecules-lipid bilayerlipid bilayer

Membrane StructureMembrane Structure

ProteinsProteins are embedded in the bilayer are embedded in the bilayer Think of raisins in raisin breadThink of raisins in raisin bread

Fluid Mosaic ModelFluid Mosaic Model

The The phospholipid bilayerphospholipid bilayer acts more like a acts more like a liquid than a solid.liquid than a solid.

The Phospholipid BilayerThe Phospholipid Bilayer

Most lipids have two fatty acids Most lipids have two fatty acids attached to glycerolattached to glycerol

The third fatty acid is replaced by a The third fatty acid is replaced by a phosphate group-phosphate group-phospholipidphospholipid

Phospholipids-polar, water-soluble head Phospholipids-polar, water-soluble head + long, nonpolar, insoluble tail+ long, nonpolar, insoluble tail

Align to form double layer with “heads” Align to form double layer with “heads” on outside and “tails” on the insideon outside and “tails” on the inside

DiffusionDiffusion

Cells maintain homeostasis by controlling Cells maintain homeostasis by controlling the movement of substances across the the movement of substances across the membranemembrane

Cells must use NRG to transport some Cells must use NRG to transport some substances…..Ex- Active Transport!substances…..Ex- Active Transport!

Other substances move across the Other substances move across the membrane with no NRG requiredmembrane with no NRG required

DiffusionDiffusion

DiffusionDiffusion is the net movement of is the net movement of particles from an area of higher particles from an area of higher concentration to an area of lower concentration to an area of lower concentration.concentration.

Goal of diffusion=Goal of diffusion=Dynamic EquilibriumDynamic Equilibrium Continuous movement with no Continuous movement with no

concentration changeconcentration change Concentration gradientConcentration gradient-difference in -difference in

concentration across spaceconcentration across space

Dynamic EquilibriumDynamic Equilibrium

Diffusion!!Diffusion!!

Osmosis-Diffusion of WaterOsmosis-Diffusion of Water

OsmosisOsmosis is the diffusion of water molecules is the diffusion of water molecules through a selectively permeable membranethrough a selectively permeable membrane Movement from high to low concentrationMovement from high to low concentration Type of Type of passive transportpassive transport!!

Isotonic solutionIsotonic solution-concentration of dissolved -concentration of dissolved substances equal to concentration inside the substances equal to concentration inside the cell…..NO NET MOVEMENT!cell…..NO NET MOVEMENT!

Isotonic SolutionIsotonic Solution

Hypotonic vs HypertonicHypotonic vs Hypertonic

HypotonicHypotonic-solution where concentration -solution where concentration of dissolved substances is of dissolved substances is lowerlower than than inside the cellinside the cell Water moves into cell…swelling!Water moves into cell…swelling! Increases cell pressure-Increases cell pressure-Turgor PressureTurgor Pressure

HypertonicHypertonic-solution where -solution where concentration of dissolved substances concentration of dissolved substances is is higher higher than inside the cellthan inside the cell Water moves out of cell…Water moves out of cell…PlasmolysisPlasmolysis

Dealing with OsmosisDealing with Osmosis

Cells must compensate for the water that Cells must compensate for the water that enters or exits the cell.enters or exits the cell.

Animal CellsAnimal Cells- Must maintain isotonic - Must maintain isotonic environmentenvironment

Plant CellsPlant Cells- Prefer a hypotonic environment- Prefer a hypotonic environment

Plants vs. AnimalsPlants vs. Animals

ProtistsProtists

Have contractile vacuoles that Have contractile vacuoles that activelyactively remove water from the cell.remove water from the cell.

Crossing the MembraneCrossing the Membrane

Diffusion through ion channels:Diffusion through ion channels: Ion ChannelsIon Channels- transport proteins with polar - transport proteins with polar

pores that ions can pass through.pores that ions can pass through.

Pore is the thickness of the membranePore is the thickness of the membrane

Ion does not have touch the nonpolar interior of Ion does not have touch the nonpolar interior of the bilayer.the bilayer.

Ion ChannelIon Channel

Facilitated DiffusionFacilitated Diffusion

Carrier proteinsCarrier proteins allow needed substances to allow needed substances to move through membrane by binding, move through membrane by binding, carrying, and releasing substances.carrying, and releasing substances.

This movement is called This movement is called facilitated diffusionfacilitated diffusion

Facilitated DiffusionFacilitated Diffusion

Carrier proteinsCarrier proteins change shape using change shape using chemical energy to move particle through chemical energy to move particle through the membranethe membrane

Once particle is passed, original protein Once particle is passed, original protein shape is restoredshape is restored

Facilitated DiffusionFacilitated Diffusion

Active TransportActive Transport

In order to move particles from a lower In order to move particles from a lower concentration to higher concentration a cell concentration to higher concentration a cell must use energy…must use energy…Active TransportActive Transport

Proton pumpsProton pumps- specialized proteins for pushing - specialized proteins for pushing different substances against the concentration different substances against the concentration gradient.gradient.

Need ATP for energy!!!!!Need ATP for energy!!!!!

Active TransportActive Transport

Sodium-Potassium PumpSodium-Potassium Pump

Four Steps to the Pump:Four Steps to the Pump: 1. Three Na ions attach to the pump.1. Three Na ions attach to the pump.

2. Pump changes shape, transporting the ions 2. Pump changes shape, transporting the ions across the membrane.across the membrane.

3. Two K ions outside bind to the pump3. Two K ions outside bind to the pump

4. Two K ions are transported are released inside the 4. Two K ions are transported are released inside the cell.cell.

Transport of Large ParticlesTransport of Large Particles

EndocytosisEndocytosis-process in which cell surrounds -process in which cell surrounds and takes in material from its environmentand takes in material from its environment Engulfed and enclosed by portion of cell Engulfed and enclosed by portion of cell

membranemembrane

ExocytosisExocytosis-expelling wastes from interior to -expelling wastes from interior to exterior environmentexterior environment

Endocytosis TypesEndocytosis Types

ExocytosisExocytosis