The Cell MembraneThe Cell Membrane

FunctionFunction

Regulates the movement of materials Regulates the movement of materials from one environment to the other.from one environment to the other.

Transports raw materials into the cell and Transports raw materials into the cell and waste out of the cell.waste out of the cell.

Prevents the entry of unwanted matter Prevents the entry of unwanted matter and the escape of needed materials.and the escape of needed materials.

Maintain a steady environment: Maintain a steady environment: HomeostasisHomeostasis

Structure:Structure:

Composed of a phospholipid bilayer with Composed of a phospholipid bilayer with a collage of many different proteins, lipids a collage of many different proteins, lipids and carbohydrates.and carbohydrates.

A Phospholipid is composed of 1 glycerol A Phospholipid is composed of 1 glycerol molecule, 2 fatty acids and 1 phosphate molecule, 2 fatty acids and 1 phosphate group. This structure causes hydrophilic group. This structure causes hydrophilic and hydrophobic regions.and hydrophobic regions.

The Fluid-Mosaic The Fluid-Mosaic Membrane Model Membrane Model

Membranes are not static; they have a fluid Membranes are not static; they have a fluid consistency.consistency.

Most membrane lipids and proteins can drift Most membrane lipids and proteins can drift about laterally in the plane of the membrane.about laterally in the plane of the membrane.

Cholesterol enhances membrane fluidity, Cholesterol enhances membrane fluidity, allows animal membranes to function in a wide allows animal membranes to function in a wide range of temperatures and also makes the range of temperatures and also makes the membrane less permeable to biological membrane less permeable to biological molecules.molecules.

Membrane Proteins:Membrane Proteins:Two Types:Two Types: Integral:Integral: Proteins that insert into the membrane Proteins that insert into the membrane

(transmembrane proteins)(transmembrane proteins) Peripheral:Peripheral: Proteins attached to the surface of Proteins attached to the surface of

the cell membrane.the cell membrane.Function:Function: TransportationTransportation EnzymesEnzymes Receptor sitesReceptor sites Cell adhesionCell adhesion Attachment to the cytoskeletonAttachment to the cytoskeleton

Carbohydrates:Carbohydrates:

Usually branched molecules of 15 or less Usually branched molecules of 15 or less sugar units.sugar units.

Some are bonded to lipids: Some are bonded to lipids: Glycolipids.Glycolipids. Most are bonded to proteins: Most are bonded to proteins:

Glycoproteins.Glycoproteins. Function: Function: Cell-cell recognition.Cell-cell recognition.

Construction of a Cell Construction of a Cell MembraneMembrane

Copy the link below to create your own cellCopy the link below to create your own cell

membrane.membrane.

http://www.wisc-online.com/objects/http://www.wisc-online.com/objects/index_tj.asp?objID=AP1101index_tj.asp?objID=AP1101

Through the Cell Through the Cell MembraneMembrane

1.1. DiffusionDiffusion

2.2. OsmosisOsmosis

3.3. Facilitated DiffusionFacilitated Diffusion

4.4. Active TransportActive Transport

5.5. Bulk TransportBulk Transport

1. Diffusion:1. Diffusion: PassivePassive movement of molecules from a region movement of molecules from a region

of high concentration to a region of low of high concentration to a region of low concentration.concentration.

((Concentration gradientConcentration gradient is the difference in is the difference in concentration between the two regions)concentration between the two regions)

Small, uncharged molecules like OSmall, uncharged molecules like O22, CO, CO22 and and

HH22O can move easily through the membrane.O can move easily through the membrane.

Works well over short distances. Once Works well over short distances. Once molecules enter the cell the rate of diffusion molecules enter the cell the rate of diffusion slows.slows.

Limits cell size.Limits cell size.

Passive TransportPassive Transport

2. Osmosis2. Osmosis Diffusion of the solvent across a Diffusion of the solvent across a

semi-permeable membrane semi-permeable membrane separating two solutions. (Diffusion separating two solutions. (Diffusion of water)of water)

Water molecules move from a region Water molecules move from a region of high concentration to a region of of high concentration to a region of low concentration.low concentration.

Direction depends on the relative Direction depends on the relative concentration of water molecules on concentration of water molecules on either side of the cell membrane.either side of the cell membrane.

Isotonic:Isotonic: Water inside the cell equals the Water inside the cell equals the water outside the cell and equal amounts water outside the cell and equal amounts of water move in and out of the cell.of water move in and out of the cell.

Hypotonic:Hypotonic: Water outside the cell is Water outside the cell is greater than that inside the cell, water greater than that inside the cell, water moves into the cell, may cause cell to burst moves into the cell, may cause cell to burst (lysis)(lysis)

Hypertonic:Hypertonic: Water inside the cell is Water inside the cell is greater than outside. Water moves out of greater than outside. Water moves out of the cell, may cause the cell to shrink the cell, may cause the cell to shrink (plasmolysis)(plasmolysis)

Osmosis: HypotonicOsmosis: Hypotonic

3. Facilitated Diffusion3. Facilitated Diffusion Assists with the movement of large Assists with the movement of large

molecules like glucose.molecules like glucose. PassivePassive movement of a substance movement of a substance

into or out of the cell by means of into or out of the cell by means of carrier proteins or channel carrier proteins or channel proteins.proteins.

Moves molecules from high to low Moves molecules from high to low regions of concentration.regions of concentration.

Carrier proteins:Carrier proteins: Transports non- Transports non-charged molecules with a specific charged molecules with a specific shape.shape.

Channel proteins:Channel proteins: Tunnel shape that Tunnel shape that transports small charged molecules.transports small charged molecules.

4. Active Transport4. Active Transport The process of moving substances The process of moving substances

against their concentration gradients. against their concentration gradients. Requires energy.Requires energy.

Examples:Examples: Kidney cells pump glucose and amino Kidney cells pump glucose and amino

acids out of the urine and back into the acids out of the urine and back into the blood.blood.

Intestinal cells pump in Intestinal cells pump in nutrients from the gut.nutrients from the gut.

Root cells pump in nutrients Root cells pump in nutrients from the soil.from the soil.

Gill cells in fish pump out Gill cells in fish pump out sodium ions.sodium ions.

Active Transport Pump:Active Transport Pump: Sodium-potassium pumpSodium-potassium pump 3 sodium ions inside the cell and 2 3 sodium ions inside the cell and 2

potassium ions outside the cell potassium ions outside the cell bind to the pump.bind to the pump.

This allows the release of energy This allows the release of energy from ATP and causes the protein from ATP and causes the protein complex to change shape.complex to change shape.

The change in shape allow the Na The change in shape allow the Na + and K+ ions to move across and + and K+ ions to move across and be released.be released.

Active Transport PumpActive Transport Pump

5. Bulk Transport5. Bulk Transport1. 1. Endocytosis:Endocytosis: The cell membrane The cell membrane

folds inward, traps and encloses a folds inward, traps and encloses a small amount of matter from the small amount of matter from the extracellular fluid. 3 types:extracellular fluid. 3 types:

EndocytosisEndocytosis Pinocytosis: Pinocytosis: The intake of a small The intake of a small

droplet of extracellular fluid. This droplet of extracellular fluid. This occurs in nearly all cell types.occurs in nearly all cell types.

Phagocytosis:Phagocytosis: The intake of a The intake of a large droplet of extracellular fluid. large droplet of extracellular fluid. This occurs in specialized cells.This occurs in specialized cells.

Receptor-assisted endocytosis:Receptor-assisted endocytosis: The intake of specific molecules The intake of specific molecules that attach to special proteins in that attach to special proteins in the cell membrane. These proteins the cell membrane. These proteins are uniquely shaped to fit the are uniquely shaped to fit the shape of a specific molecule.shape of a specific molecule.

Bulk TransportBulk Transport2. 2. Exocytosis:Exocytosis: The reverse of The reverse of

endocytosis: A vesicle from inside the endocytosis: A vesicle from inside the cell moves to the cell membrane. The cell moves to the cell membrane. The vesicle fuses to the membrane and vesicle fuses to the membrane and the contents are secreted the contents are secreted