The Plasma The Plasma MembraneMembrane

IB Biology HLIB Biology HLE. McIntyreE. McIntyre

History of the Plasma MembraneHistory of the Plasma Membrane 1665: Robert Hooke 1665: Robert Hooke 1895: Charles Overton - composed of lipids 1895: Charles Overton - composed of lipids 1900-1920’s: must be a phospholipid 1900-1920’s: must be a phospholipid 1925: E. Gorter and G. Grendel - 1925: E. Gorter and G. Grendel -

phospholipid phospholipid bilayerbilayer 1935: J.R. Danielli and H. Davson – proteins 1935: J.R. Danielli and H. Davson – proteins

also part, proposed the also part, proposed the Sandwich ModelSandwich Model 1950’s: J.D. Robertson – proposed the 1950’s: J.D. Robertson – proposed the Unit Unit

Membrane ModelMembrane Model 1972: S.J. Singer and G.L. Nicolson – 1972: S.J. Singer and G.L. Nicolson –

proposed proposed Fluid Mosaic ModelFluid Mosaic Model

Plasma Membrane is made of Plasma Membrane is made of PhospholipidsPhospholipids

Gorter + Grendel Gorter + Grendel – Red Blood Cells analyzedRed Blood Cells analyzed– Enough for Phospholipid bilayerEnough for Phospholipid bilayer– Polar heads face out and Polar heads face out and

Nonpolar tails face in Nonpolar tails face in– Does not explain why some Does not explain why some

nonlipids are permeable nonlipids are permeable

Plasma Membrane ModelsPlasma Membrane Models

Sandwich ModelSandwich Model(Danielli + Davson)(Danielli + Davson)2 layers of globular proteins with phospholipid 2 layers of globular proteins with phospholipid inside to make a layer and then join 2 layers inside to make a layer and then join 2 layers together to make a channel for molecules to together to make a channel for molecules to passpass

Unit Membrane Model Unit Membrane Model (Robertson)(Robertson)Outer layer of protein with phospholipid bilayer Outer layer of protein with phospholipid bilayer inside, believed all cells same composition, inside, believed all cells same composition, does not explain how some molecules pass does not explain how some molecules pass through or the use of proteins with nonpolar through or the use of proteins with nonpolar parts, used transmission electron microscopyparts, used transmission electron microscopy

Fluid Mosaic Model Fluid Mosaic Model (Singer + Nicolson)(Singer + Nicolson)Phospholipid bilayer with proteins partially or Phospholipid bilayer with proteins partially or fully imbedded, electron micrographs of freeze-fully imbedded, electron micrographs of freeze-fractured membranefractured membrane

Which membrane model is correct?Which membrane model is correct?

1) Rapidly freeze specimen1) Rapidly freeze specimen

2) Use special knife to cut membrane in half2) Use special knife to cut membrane in half

3) Apply a carbon + platinum coating to the surface3) Apply a carbon + platinum coating to the surface

4) Use scanning electron microscope to see the surface4) Use scanning electron microscope to see the surface

According to the electron micrograph which membrane model is correct?According to the electron micrograph which membrane model is correct?

Why?Why?

Fluid-Mosaic ModelFluid-Mosaic Model

Fluid-Mosaic ModelFluid-Mosaic Model FluidFluid – the plasma membrane is the consistency of olive oil at body – the plasma membrane is the consistency of olive oil at body

temperature, due to unsaturated phospholipids. (cells differ in the temperature, due to unsaturated phospholipids. (cells differ in the amount of unsaturated to saturated fatty acid tails) amount of unsaturated to saturated fatty acid tails)

Most of the lipids and some proteins drift laterally on either side. Most of the lipids and some proteins drift laterally on either side. Phospholipids do not switch from one layer to the next.Phospholipids do not switch from one layer to the next.

Cholesterol affects fluidity: at body temperature it lessens fluidity by Cholesterol affects fluidity: at body temperature it lessens fluidity by restraining the movement of phospholipids, at colder temperatures it restraining the movement of phospholipids, at colder temperatures it adds fluidity by not allowing phospholipids to pack close together.adds fluidity by not allowing phospholipids to pack close together.

MosaicMosaic – membrane proteins form a collage that differs on either – membrane proteins form a collage that differs on either side of the membrane and from cell to cell (greater than 50 types of side of the membrane and from cell to cell (greater than 50 types of proteins), proteins span the membrane with hydrophilic portions facing proteins), proteins span the membrane with hydrophilic portions facing out and hydrophobic portions facing in. Provides the functions of the out and hydrophobic portions facing in. Provides the functions of the membranemembrane

Structure of the Plasma MembraneStructure of the Plasma Membrane

Structure of the Plasma MembraneStructure of the Plasma Membrane Phospholipid bilayerPhospholipid bilayer

PhospholipidPhospholipid– Hydrophilic headHydrophilic head– Hydrophobic tailsHydrophobic tails

CholesterolCholesterol

ProteinsProteins– Transmembrane/Transmembrane/

Intrinsic/Intrinsic/IntegralIntegral

– Peripheral/ExtrinsicPeripheral/Extrinsic

Cytoskeletal filamentsCytoskeletal filaments

Carbohydrate chainCarbohydrate chain

GlycoproteinsGlycoproteins

GlycolipidsGlycolipids

Label the Blank Diagram of the Label the Blank Diagram of the Plasma MembranePlasma Membrane

Phospholipid bilayerPhospholipid bilayer

PhospholipidPhospholipid– Hydrophilic headHydrophilic head– Hydrophobic tailsHydrophobic tails

CholesterolCholesterol

ProteinsProteins– Transmembrane/Transmembrane/

Intrinsic/IntegralIntrinsic/Integral– Peripheral/ExtrinsicPeripheral/Extrinsic

Cytoskeletal filamentsCytoskeletal filaments

Carbohydrate chainCarbohydrate chain

GlycoproteinsGlycoproteins

GlycolipidsGlycolipids

Proteins of the Plasma Membrane Proteins of the Plasma Membrane Provide 6 Membrane Functions:Provide 6 Membrane Functions:

1) 1) Transport ProteinsTransport Proteins

2) 2) Receptor ProteinsReceptor Proteins

3) 3) Enzymatic ProteinsEnzymatic Proteins

4) 4) Cell Recognition ProteinsCell Recognition Proteins

5) 5) Attachment ProteinsAttachment Proteins

6) 6) Intercellular Junction Intercellular Junction

ProteinsProteins

1)1) Transport ProteinsTransport Proteins

Channel ProteinsChannel Proteins – – channel for lipid channel for lipid insoluble molecules insoluble molecules and ions to pass freely and ions to pass freely throughthrough

Carrier ProteinsCarrier Proteins – bind – bind to a substance and to a substance and carry it across carry it across membrane, change membrane, change shape in processshape in process

2)2) Receptor ProteinsReceptor Proteins

– – Bind to chemical Bind to chemical messengers (Ex. messengers (Ex. hormones) which hormones) which sends a message into sends a message into the cell causing the cell causing cellular reactioncellular reaction

3)3) Enzymatic ProteinsEnzymatic Proteins

– – Carry out enzymatic Carry out enzymatic reactions right at the reactions right at the membrane when a membrane when a substrate binds to the substrate binds to the active siteactive site

4)4) Cell Recognition ProteinsCell Recognition Proteins

– – Glycoproteins (and Glycoproteins (and glycolipids) on glycolipids) on extracellular surface extracellular surface serve as ID tags serve as ID tags (which species, type of (which species, type of cell, individual). cell, individual). Carbohydrates are Carbohydrates are short branched chains short branched chains of less than 15 sugarsof less than 15 sugars

5)5) Attachment ProteinsAttachment Proteins

- Attach to cytoskeleton (to Attach to cytoskeleton (to maintain cell shape and stabilize maintain cell shape and stabilize proteins) and/or the extracellular proteins) and/or the extracellular matrix (integrins connect to matrix (integrins connect to both).both).

- Extracellular Matrix – protein Extracellular Matrix – protein fibers and carbohydrates fibers and carbohydrates secreted by cells and fills the secreted by cells and fills the spaces between cells and spaces between cells and supports cells in a tissue. supports cells in a tissue.

- Extracellular matrix can Extracellular matrix can influence activity inside the cell influence activity inside the cell and coordinate the behavior of and coordinate the behavior of all the cells in a tissue.all the cells in a tissue.

6)6) Intercellular Junction ProteinsIntercellular Junction Proteins

– – Bind cells togetherBind cells together

– Tight junctionsTight junctions

– Gap junctionsGap junctions

• Materials must move Materials must move in and out of the cell in and out of the cell through the plasma through the plasma membrane.membrane.

• Some materials Some materials move between the move between the phospholipids.phospholipids.

• Some materials Some materials move through the move through the proteins.proteins.

How do materials move into and How do materials move into and out of the cell?out of the cell?

Plasma Membrane TransportPlasma Membrane Transport

• Molecules move across the plasma Molecules move across the plasma membrane by:membrane by:

What are three types of What are three types of passive transport?passive transport?

1)1) DiffusionDiffusion

2)2) Facilitated DiffusionFacilitated Diffusion

3)3) OsmosisOsmosisATP energy is ATP energy is notnot

needed to move the needed to move the molecules through.molecules through.

Passive Transport 1: DiffusionPassive Transport 1: Diffusion

• Molecules can move directly Molecules can move directly through the phospholipids of the through the phospholipids of the plasma membraneplasma membrane

This is called …This is called …

What is Diffusion?What is Diffusion?

• Diffusion is the net Diffusion is the net movement of molecules movement of molecules from a high from a high concentration to a low concentration to a low concentration until concentration until equally distributed.equally distributed.

• Diffusion rate is related Diffusion rate is related to temperature, to temperature, pressure, state of matter, pressure, state of matter, size of concentration size of concentration gradient, and surface gradient, and surface area of membrane.area of membrane.

http://www.biologycorner.com/resources/diffusion-animated.gif

What molecules pass through the What molecules pass through the plasma membrane by diffusion?plasma membrane by diffusion?

• Gases (oxygen, carbon Gases (oxygen, carbon dioxide)dioxide)

• Water molecules (rate Water molecules (rate slow due to polarity)slow due to polarity)

• Lipids (steroid Lipids (steroid hormones)hormones)

• Lipid soluble molecules Lipid soluble molecules (hydrocarbons, alcohols, (hydrocarbons, alcohols, some vitamins)some vitamins)

• Small noncharged Small noncharged molecules (NHmolecules (NH33))

Why is diffusion important to cells Why is diffusion important to cells and humans?and humans?

• Cell respirationCell respiration• Alveoli of lungsAlveoli of lungs• CapillariesCapillaries• Red Blood CellsRed Blood Cells• Medications: time-Medications: time-

release capsulesrelease capsules

Passive Transport 2: Facilitated Passive Transport 2: Facilitated DiffusionDiffusion

• Molecules can move through the Molecules can move through the plasma membrane with the aid of plasma membrane with the aid of transport proteinstransport proteins

This is called …This is called …

What is Facilitated Diffusion?What is Facilitated Diffusion?

• Facilitated diffusion Facilitated diffusion is the net movement is the net movement of molecules from a of molecules from a high concentration to high concentration to a low concentration a low concentration with the aid of with the aid of channel or carrier channel or carrier proteinsproteins..

What molecules move through the plasma What molecules move through the plasma membrane by facilitated diffusion?membrane by facilitated diffusion?

• IonsIons (Na(Na++, K, K++, Cl, Cl--))

• Sugars (Glucose)Sugars (Glucose)

• Amino AcidsAmino Acids

• Small water soluble Small water soluble moleculesmolecules

• Water (faster rate)Water (faster rate)

How do molecules move through the How do molecules move through the plasma membrane by facilitated diffusion?plasma membrane by facilitated diffusion?

• Channel and Carrier proteins are specific:Channel and Carrier proteins are specific:• Channel Proteins allow ions, small solutes, and water Channel Proteins allow ions, small solutes, and water

to passto pass• Carrier Proteins move glucose and amino acidsCarrier Proteins move glucose and amino acids• Facilitated diffusion is rate limited, by the number of Facilitated diffusion is rate limited, by the number of

proteins channels/carriers present in the membrane.proteins channels/carriers present in the membrane.

Specific Types of Facilitated Specific Types of Facilitated DiffusionDiffusion

Counter TransportCounter Transport – the transport – the transport of two substances at the same time of two substances at the same time in opposite directions, without ATP. in opposite directions, without ATP. Protein carriers are called Protein carriers are called AntiportsAntiports..

Co-transport Co-transport – the transport of – the transport of two substances at the same time in two substances at the same time in the same direction, without ATP. the same direction, without ATP. Protein carriers are called Protein carriers are called SymportsSymports..

Gated ChannelsGated Channels – receptors – receptors combined with channel proteins. combined with channel proteins. When a chemical messenger binds When a chemical messenger binds to a receptor, a gate opens to allow to a receptor, a gate opens to allow ions to flow through the channel. ions to flow through the channel.

Why is facilitated diffusion important Why is facilitated diffusion important to cells and humans?to cells and humans?

• Cells obtain food for Cells obtain food for cell respirationcell respiration

• Neurons Neurons communicatecommunicate

• Small intestine cells Small intestine cells transport food to transport food to bloodstreambloodstream

• Muscle cells contractMuscle cells contract

Passive Transport 3: OsmosisPassive Transport 3: Osmosis

• Water Molecules can move directly Water Molecules can move directly through the phospholipids of the through the phospholipids of the plasma membraneplasma membrane

This is called …This is called …

What is Osmosis?What is Osmosis?

• Osmosis is the diffusion of water through a Osmosis is the diffusion of water through a semipermeable membrane. Water molecules bound semipermeable membrane. Water molecules bound to solutes cannot pass due to size, only unbound to solutes cannot pass due to size, only unbound molecules. Free water molecules collide, bump into molecules. Free water molecules collide, bump into the membrane, and pass through.the membrane, and pass through.

Osmosis in actionOsmosis in action• What will happen in the What will happen in the

U-tube if water freely U-tube if water freely moves through the moves through the membrane but glucose membrane but glucose can not pass?can not pass?

• Water moves from side with Water moves from side with high concentration of water to high concentration of water to side with lower concentration side with lower concentration of water. Movement stops of water. Movement stops when osmotic pressure when osmotic pressure equals hydrostatic pressure.equals hydrostatic pressure.

Why is osmosis important to cells Why is osmosis important to cells and humans?and humans?

• Cells remove water Cells remove water produced by cell produced by cell respiration.respiration.

• Large intestine cells Large intestine cells transport water to transport water to bloodstreambloodstream

• Kidney cells form Kidney cells form urineurine

Osmosis and TonicityOsmosis and Tonicity

Tonicity refers to the total solute Tonicity refers to the total solute concentration of the solution outside the concentration of the solution outside the cell.cell.

What are the three types of tonicity?What are the three types of tonicity?1)1) IsotonicIsotonic

2)2) HypotonicHypotonic

3)3) HypertonicHypertonic

IsotonicIsotonic Solutions that have the Solutions that have the samesame concentration of concentration of

solutes as the suspended cell.solutes as the suspended cell.

What will happen to a cell placed in an Isotonic What will happen to a cell placed in an Isotonic solution?solution?

The cell will have no net movement of water and The cell will have no net movement of water and will stay the same size.will stay the same size.

Ex. Blood plasma has high concentration of Ex. Blood plasma has high concentration of albumin molecules to make it isotonic to tissues.albumin molecules to make it isotonic to tissues.

HypotonicHypotonic Solutions that have a Solutions that have a lowerlower solute concentration solute concentration

than the suspended cell.than the suspended cell.

What will happen to a cell placed in a Hypotonic What will happen to a cell placed in a Hypotonic solution?solution?

The cell will gain water and swell.The cell will gain water and swell. If the cell bursts, then we call this lysis. (Red blood If the cell bursts, then we call this lysis. (Red blood

cells = hemolysis)cells = hemolysis) In plant cells with rigid cell walls, this creates In plant cells with rigid cell walls, this creates

turgor pressure.turgor pressure.

HypertonicHypertonic Solutions that have a Solutions that have a higherhigher solute concentration solute concentration

than a suspended cell.than a suspended cell.

What will happen to a cell placed in a Hypertonic What will happen to a cell placed in a Hypertonic solution?solution?

The cell will lose water and shrink. (Red blood The cell will lose water and shrink. (Red blood cells = crenation)cells = crenation)

In plant cells, the central vacuole will shrink and In plant cells, the central vacuole will shrink and the plasma membrane will pull away from the cell the plasma membrane will pull away from the cell wall causing the cytoplasm to shrink called wall causing the cytoplasm to shrink called plasmolysis.plasmolysis.

Review: Passive TransportReview: Passive Transport

• DiffusionDiffusion – O – O22 moves in and CO moves in and CO22 moves out moves out during cell respirationduring cell respiration

• Facilitated DiffusionFacilitated Diffusion – glucose and amino – glucose and amino acids enter cell for cell respirationacids enter cell for cell respiration

• OsmosisOsmosis – cell removal or addition of water – cell removal or addition of water

Review TonicityReview Tonicity What will happen to a red blood cell in a What will happen to a red blood cell in a

hypertonic solution?hypertonic solution? What will happen to a red blood cell in an What will happen to a red blood cell in an

isotonic solution?isotonic solution? What will happen to a red blood cell in a What will happen to a red blood cell in a

hypotonic solution?hypotonic solution?

1) Active Transport1) Active Transport2) Exocytosis2) Exocytosis3) Endocytosis3) Endocytosis

– PhagocytosisPhagocytosis– PinocytosisPinocytosis– Receptor-Mediated Receptor-Mediated

endocytosisendocytosis

What are three types of What are three types of Active transport?Active transport?

ATP energy is ATP energy is requiredrequired to move the to move the molecules through.molecules through.

Active TransportActive Transport Molecules move from areas of low Molecules move from areas of low

concentration to areas of high concentration concentration to areas of high concentration with the aid of ATP energy.with the aid of ATP energy.

Requires protein carriers called Pumps.Requires protein carriers called Pumps.

The Importance of Active TransportThe Importance of Active Transport Bring in essential molecules: ions, Bring in essential molecules: ions,

amino acids, glucose, nucleotidesamino acids, glucose, nucleotides Rid cell of unwanted molecules (Ex. Rid cell of unwanted molecules (Ex.

sodium from urine in kidneys)sodium from urine in kidneys) Maintain internal conditions different Maintain internal conditions different

from the environmentfrom the environment Regulate the volume of cells by Regulate the volume of cells by

controlling osmotic potentialcontrolling osmotic potential Control cellular pHControl cellular pH Re-establish concentration Re-establish concentration

gradients to run facilitated diffusion. gradients to run facilitated diffusion. (Ex. Sodium-Potassium pump and (Ex. Sodium-Potassium pump and Proton pumps)Proton pumps)

The Sodium-Potassium PumpThe Sodium-Potassium Pump 3 Sodium ions move out of 3 Sodium ions move out of

the cell and then 2 the cell and then 2 Potassium ions move into Potassium ions move into the cell.the cell.

Driven by the splitting of Driven by the splitting of ATP to provide energy and ATP to provide energy and conformational change to conformational change to proteins by adding and then proteins by adding and then taking away a phosphate taking away a phosphate group.group.

Used to establish an Used to establish an electrochemical gradient electrochemical gradient across neuron cell across neuron cell membranes.membranes. http://www.biologie.uni-hamburg.de/b-online/library/biology107/bi107vc/fa99/terry/images/ATPpumA.gif

Active Transport 2: ExocytosisActive Transport 2: Exocytosis Movement of large Movement of large

molecules bound in molecules bound in vesicles vesicles out ofout of the cell the cell with the aid of ATP with the aid of ATP energy. Vesicle fuses energy. Vesicle fuses with the plasma with the plasma membrane to eject membrane to eject macromolecules.macromolecules.

Ex. Proteins, Ex. Proteins, polysaccharides, polysaccharides, polynucleotides, whole polynucleotides, whole cells, hormones, mucus, cells, hormones, mucus, neurotransmitters, wasteneurotransmitters, waste

Active Transport 3: EndocytosisActive Transport 3: Endocytosis

Movement of large molecules Movement of large molecules intointo the cell the cell by engulfing them in vesicles, using ATP by engulfing them in vesicles, using ATP energy.energy.

Three types of Endocytosis:Three types of Endocytosis:– PhagocytosisPhagocytosis– PinocytosisPinocytosis– Receptor-mediated endocytosisReceptor-mediated endocytosis

PhagocytosisPhagocytosis ““Cellular Eating” – engulfing large Cellular Eating” – engulfing large

molecules, whole cells, bacteria molecules, whole cells, bacteria Ex. Macrophages ingesting bacteria or worn Ex. Macrophages ingesting bacteria or worn

out red blood cells.out red blood cells. Ex. Unicellular organisms engulfing food Ex. Unicellular organisms engulfing food

particles.particles.

PinocytosisPinocytosis ““Cellular Drinking” – engulfing liquids and Cellular Drinking” – engulfing liquids and

small molecules dissolved in liquids; small molecules dissolved in liquids; unspecific what enters.unspecific what enters.

Ex. Intestinal cells, Kidney cells, Plant root Ex. Intestinal cells, Kidney cells, Plant root cellscells

Receptor-Mediated EndocytosisReceptor-Mediated Endocytosis Movement of very specific Movement of very specific

molecules into the cell with the molecules into the cell with the use of vesicles coated with the use of vesicles coated with the protein clathrin. protein clathrin.

Coated pits are specific Coated pits are specific locations coated with clathrin locations coated with clathrin and receptors. When specific and receptors. When specific molecules (ligands) bind to the molecules (ligands) bind to the receptors, then this stimulates receptors, then this stimulates the molecules to be engulfed the molecules to be engulfed into a coated vesicle.into a coated vesicle.

Ex. Uptake of cholesterol (LDL) Ex. Uptake of cholesterol (LDL) by animal cellsby animal cells

Review Types of EndocytosisReview Types of Endocytosis

What is phagocytosis?What is phagocytosis?

What is pinocytosis?What is pinocytosis?

What is receptor-What is receptor-mediated endocytosis?mediated endocytosis?

Types of Cell JunctionsTypes of Cell Junctions

In Animal Cells:In Animal Cells:

Tight JunctionsTight Junctions

DesmosomesDesmosomes

Gap JunctionsGap Junctions

In Plant Cells:In Plant Cells:

PlasmodesmataPlasmodesmata

Tight JunctionsTight Junctions Transmembrane Proteins of opposite cells Transmembrane Proteins of opposite cells

attach in a tight zipper-like fashionattach in a tight zipper-like fashion No leakageNo leakage Ex. Intestine, Kidneys, Epithelium of skinEx. Intestine, Kidneys, Epithelium of skin

DesmosomesDesmosomes Cytoplasmic plaques of two cells bind with Cytoplasmic plaques of two cells bind with

the aid of intermediate filaments of keratin the aid of intermediate filaments of keratin Allows for stretchingAllows for stretching Ex. Stomach, Bladder, HeartEx. Stomach, Bladder, Heart

Gap JunctionsGap Junctions Channel proteins of opposite cells join together Channel proteins of opposite cells join together

providing channels for ions, sugars, amino providing channels for ions, sugars, amino acids, and other small molecules to pass.acids, and other small molecules to pass.

Allows communication between cells.Allows communication between cells. Ex. Heart muscle, animal embryosEx. Heart muscle, animal embryos

PlasmodesmataPlasmodesmata Channels between the cell walls of plant cells Channels between the cell walls of plant cells

that are lined with the plasma membranes of that are lined with the plasma membranes of adjacent cells and smooth ER runs through.adjacent cells and smooth ER runs through.

Allows for the exchange of cytosol between Allows for the exchange of cytosol between adjacent cells; moving water, small solutes, adjacent cells; moving water, small solutes, sugar, and amino acids.sugar, and amino acids.

Ex. Xylem and Phloem in PlantsEx. Xylem and Phloem in Plants

Review Types of Cell JunctionsReview Types of Cell Junctions What is the difference between a What is the difference between a

plasmodesmata, tight junction, gap junction, plasmodesmata, tight junction, gap junction, and desmosome?and desmosome?

ReferencesReferences

Campbell, Neil A., Jane B. Reece, and Lawrence G. Campbell, Neil A., Jane B. Reece, and Lawrence G. Mitchell. (1999). Mitchell. (1999). BiologyBiology. Reading: Addison Wesley . Reading: Addison Wesley Longman, Inc.Longman, Inc.

Mader, Sylvia S. (1996). Mader, Sylvia S. (1996). BiologyBiology. Boston: Times Mirror . Boston: Times Mirror Higher Education Group, Inc.Higher Education Group, Inc.

Raven, Peter H. and Johnson, George B. (1989). Raven, Peter H. and Johnson, George B. (1989). BiologyBiology. Boston: TimesMirror/Mosby College . Boston: TimesMirror/Mosby College Publishing.Publishing.