MembranesMembranes

Structure and FunctionStructure and Function

Membrane StructureMembrane Structure

Phospholipid Bi-layerPhospholipid Bi-layer Contains Different Types of ProteinsContains Different Types of Proteins

– Channel proteinsChannel proteins– Protein Pumps proteinsProtein Pumps proteins– Adhesion proteinsAdhesion proteins– Cell-to-Cell Communication proteinsCell-to-Cell Communication proteins– Hormone Receptor proteinsHormone Receptor proteins– Immobilized EnzymesImmobilized Enzymes

Fluid Mosaic ModelFluid Mosaic Model

Phospholipid Bi-layerPhospholipid Bi-layer

ContainsContains GlycoproteinsGlycoproteins Integral ProteinsIntegral Proteins Peripheral ProteinsPeripheral Proteins CholesterolCholesterol

Channel proteinsChannel proteins

Integral protein: embedded across bi-layerIntegral protein: embedded across bi-layer Allows for movement of molecules across Allows for movement of molecules across

cell membranecell membrane

Protein PumpsProtein Pumps

Integral proteinIntegral protein Transports molecules across membranes Transports molecules across membranes

by changing shapeby changing shape

Adhesion proteinsAdhesion proteins

Connects internal Connects internal cytoskeleton to cytoskeleton to external points of external points of attachmentattachment

Secures cells of Secures cells of multi-cellular multi-cellular organisms in placeorganisms in place

Cell-to-Cell Communication Cell-to-Cell Communication proteinsproteins

Cells within the Cells within the same organism use same organism use membrane proteins membrane proteins to recognize each to recognize each otherother

Often use Often use glycoproteinsglycoproteins

Major importance Major importance to immune systemto immune system

Hormone Receptor proteinsHormone Receptor proteins

Hormones bind to Hormones bind to cell surface proteinscell surface proteins

Initiates a series of Initiates a series of reactions within cellreactions within cell

Results in cellular Results in cellular response such gene response such gene expression (making expression (making more or less of a more or less of a protein)protein)

Immobilized EnzymesImmobilized Enzymes

Many enzymes used by cells are Many enzymes used by cells are embedded within membranesembedded within membranes

Useful in keeping certain Useful in keeping certain reactions in specific parts of the reactions in specific parts of the cellcell

Membrane FunctionMembrane Function

Boundary Separates Two EnvironmentsBoundary Separates Two Environments Selectively PermeableSelectively Permeable Passive TransportPassive Transport

– Simple DiffusionSimple Diffusion– Facilitated DiffusionFacilitated Diffusion

Active TransportActive Transport– Protein PumpsProtein Pumps

Endocytosis / ExocytosisEndocytosis / Exocytosis

Selectively PermeableSelectively Permeable

Membranes and their proteins allow Membranes and their proteins allow only certain molecules to crossonly certain molecules to cross

Diffusion: movement of a substance Diffusion: movement of a substance from an area of high concentration to from an area of high concentration to low concentrationlow concentration

Osmosis: movement of water from Osmosis: movement of water from an area of low solute concentration an area of low solute concentration to highto high

DiffusionDiffusion

OsmosisOsmosis

Passive TransportPassive Transport

The movement of a molecule across a The movement of a molecule across a membrane from high to low membrane from high to low concentrationconcentration

Molecules move with the concentration Molecules move with the concentration gradientgradient

Simple DiffusionSimple Diffusion– No proteins neededNo proteins needed

Facilitated DiffusionFacilitated Diffusion– Membrane proteins requiredMembrane proteins required

Simple DiffusionSimple Diffusion

Small, uncharged Small, uncharged molecules can molecules can move directly move directly across membraneacross membrane

Includes gases Includes gases (CO(CO2 2 and 0and 022 ) and ) and waterwater

Facilitated DiffusionFacilitated Diffusion Uses either protein channels or Uses either protein channels or

transporters (change shape)transporters (change shape)

ChannelChannel TransporterTransporter

Passive TransportPassive Transport

Active TransportActive Transport

Movement of molecules across a Movement of molecules across a membrane from low concentrations membrane from low concentrations to highto high

Molecules move against the Molecules move against the concentration gradientconcentration gradient

Requires a protein transporter Requires a protein transporter (pump) and energy supplied by ATP(pump) and energy supplied by ATP

Ex. sodium/potassium pumpEx. sodium/potassium pump

Active TransportActive Transport

Active TransportActive Transport

Passive Vs. Active TransportPassive Vs. Active Transport

EndocytosisEndocytosis

Cell membrane surrounds and Cell membrane surrounds and engulfs food particle or extra-cellular engulfs food particle or extra-cellular fluidfluid

Results in vesicle inside cellResults in vesicle inside cell Phagocytosis: engulfing large Phagocytosis: engulfing large

particles like bacteriaparticles like bacteria Pinocytosis: engulfing extra-cellular Pinocytosis: engulfing extra-cellular

fluid and whatever it might containfluid and whatever it might contain

ExocytosisExocytosis

Opposite of endocytosisOpposite of endocytosis Vesicle containing secretory proteins Vesicle containing secretory proteins

or wastes joins with plasma or wastes joins with plasma membranemembrane

Molecules inside vesicle are then Molecules inside vesicle are then released outside of the cellreleased outside of the cell

SummarySummary

Review QuestionsReview Questions

Name 5 types of membrane proteins Name 5 types of membrane proteins and describe their functionsand describe their functions

What is the most significant difference What is the most significant difference between passive and active transport?between passive and active transport?

Why are transport proteins necessary Why are transport proteins necessary in facilitated diffusion?in facilitated diffusion?

Why does active transport require Why does active transport require energy?energy?

ProblemsProblems

#1#1

The internal cell The internal cell concentration of concentration of sucrose is 1M, the sucrose is 1M, the external external concentration is .1M, concentration is .1M, how might a cell how might a cell raise the internal raise the internal concentration to 2M concentration to 2M without using a without using a metabolic pathway?metabolic pathway?

#2#2

What might What might happen if a cell happen if a cell continually continually secreted enzymes, secreted enzymes, but never but never participated in participated in endocytosis?endocytosis?