AS Biology. Foundation. Cell membranes and Transport1 AS Biology FOUNDATION Chapter 4 CELL MEMBRANES and TRANSPORT Visit

AS Biology. Foundation. Cell AS Biology. Foundation. Cell membranes and Transportmembranes and Transport

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AS BiologyAS BiologyFOUNDATIONFOUNDATION

Chapter 4Chapter 4

CELL MEMBRANESCELL MEMBRANESandand

TRANSPORTTRANSPORTVisit www.worldofteaching.comFor 100’s of free powerpoints


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The CellThe Cell


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Learning ObjectivesLearning Objectives1.1. Describe the fluid mosaic model of membrane structure and explain the Describe the fluid mosaic model of membrane structure and explain the

underlying reasons for this structure.underlying reasons for this structure.

2.2. Outline the roles of phospholipids, cholesterol, glycolipids, proteins and Outline the roles of phospholipids, cholesterol, glycolipids, proteins and glycoproteins in membranes.glycoproteins in membranes.

3.3. Outline the roles of the plasma membrane, and the roles of membranes Outline the roles of the plasma membrane, and the roles of membranes within cells.within cells.

4.4. Describe and explain how molecules can get in and out of cells (cross Describe and explain how molecules can get in and out of cells (cross cell membranes) by the processes of diffusion, facilitated diffusion, cell membranes) by the processes of diffusion, facilitated diffusion, osmosis, active transport, endocytosis and exocytosis.osmosis, active transport, endocytosis and exocytosis.

5.5. Describe the effects on animal and plant cells of immersion in solutions Describe the effects on animal and plant cells of immersion in solutions of different water potential.of different water potential.

6.6. Describe the features of the gaseous exchange surface of mammalian Describe the features of the gaseous exchange surface of mammalian lung.lung.

7.7. Describe the features of root hairs that enable the uptake of ions by Describe the features of root hairs that enable the uptake of ions by active transport.active transport.


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Key words you should knowKey words you should know

Phospholipids Phospholipids SolutionSolution PinocytosisPinocytosis PolarPolar SoluteSolute MicropinocytosisMicropinocytosis HydrophilicHydrophilic SolventSolvent ExocytosisExocytosis HydrophobicHydrophobic Partially permeablePartially permeable Gaseous Gaseous

exchangeexchange MicellesMicelles Water potentialWater potential AlveoliAlveoli Phospholipid bilayerPhospholipid bilayer Solute PotentialSolute Potential Root hairRoot hair Fluid mosaic modelFluid mosaic model Pressure PotentialPressure Potential Surface areaSurface area GlycoproteinsGlycoproteins TurgidTurgid EpidermisEpidermis GlycolipidsGlycolipids PlasmolysisPlasmolysis Passive transportPassive transport CholesterolCholesterol PlasmolysedPlasmolysed ProteinsProteins Incipient plasmolysisIncipient plasmolysis Transport proteinsTransport proteins Active transportActive transport EnzymesEnzymes Carrier proteinCarrier protein Receptor moleculesReceptor molecules Bulk transportBulk transport DiffusionDiffusion EndocytosisEndocytosis Concentration gradientConcentration gradient PhagocytosisPhagocytosis Facilitated diffusionFacilitated diffusion PhagocytesPhagocytes OsmosisOsmosis Phagocytic vacuolesPhagocytic vacuoles


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Cell membraneCell membrane All living things are surrounded by a membrane.All living things are surrounded by a membrane.A cell membrane is also known as plasma A cell membrane is also known as plasma membrane.membrane.Controls exchange of materials such as nutrients Controls exchange of materials such as nutrients and waste between cells and their environment.and waste between cells and their environment.Has other important functions for example to Has other important functions for example to enable cells to receive hormones.enable cells to receive hormones.

To understand the function of anything in biology, To understand the function of anything in biology, you must study the structure first!you must study the structure first!


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Cell Membranes from Opposing Cell Membranes from Opposing Neurons (TEM x436,740). Neurons (TEM x436,740).

}} cell cell membranemembrane

7nm wide7nm wide

Cell membrane Cell membrane {{

Nerve cellNerve cell

Nerve cellNerve cell

Gap between Gap between cellscells


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HYDROPHILIC heads HYDROPHILIC heads (water liking)(water liking)-Attracted to the -Attracted to the water water

called POLARcalled POLAR

HYDROPHOBIC tails HYDROPHOBIC tails (water fearing)(water fearing)-Not attracted to -Not attracted to the waterthe water

called NON-POLARcalled NON-POLAR

Cell membranes are made Cell membranes are made of PHOSPHOLIPIDsof PHOSPHOLIPIDs

A PhospholipidA Phospholipid


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Phospholipids are important structural components of cell Phospholipids are important structural components of cell membranes. Phospholipids are modified so that a membranes. Phospholipids are modified so that a

phosphate groupphosphate group (PO4-) replaces one of the three fatty acids (PO4-) replaces one of the three fatty acids normally found on a lipid. The addition of this group makes a normally found on a lipid. The addition of this group makes a

polar "head" and two nonpolar "tails".polar "head" and two nonpolar "tails".


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A phospholipidA phospholipidHYDROPHILIC HEADHYDROPHILIC HEADAt the other end of the phospholipid is a At the other end of the phospholipid is a

phosphate group and several double phosphate group and several double bonded oxygens. The atoms at this bonded oxygens. The atoms at this end of the molecule are not shared end of the molecule are not shared equally. This end of the molecule has equally. This end of the molecule has a charge and is attracted to water. It a charge and is attracted to water. It is POLARis POLAR

HYDROPHOBIC TAILSHYDROPHOBIC TAILSThe two long chains coming off of the The two long chains coming off of the

bottom of this molecule are made up bottom of this molecule are made up of carbon and hydrogen. Because of carbon and hydrogen. Because both of these elements share their both of these elements share their electrons evenly these chains have no electrons evenly these chains have no charge. They are NON POLAR. charge. They are NON POLAR. Molecules with no charge are not Molecules with no charge are not attracted to water; as a result water attracted to water; as a result water molecules tend to push them out of molecules tend to push them out of the way as they are attracted to each the way as they are attracted to each other. This causes molecules with no other. This causes molecules with no charge not to dissolve in water. charge not to dissolve in water.

3D model of 3D model of a a PhospholipidPhospholipid


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A Phospholipid BilayerA Phospholipid BilayerPhospholipids can form: Phospholipids can form:

BILAYERSBILAYERS

-2 layers of -2 layers of phospholipids withphospholipids with

hydrophobic tails hydrophobic tails protected inside by protected inside by the hydrophilic heads.the hydrophilic heads.

The PHOSPHOLIPIDThe PHOSPHOLIPIDBILAYER is the basicBILAYER is the basicstructure of structure of

membranes.membranes.


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Structure of the cell membraneStructure of the cell membranePhospholipidsPhospholipidsCell membranes are made mainly Cell membranes are made mainly

of phospholipids. They have:of phospholipids. They have:

HYDROPHILIC heads (water liking)HYDROPHILIC heads (water liking)-Attracted to the water POLAR-Attracted to the water POLARHYDROPHOBIC tails (water HYDROPHOBIC tails (water

fearing)fearing)-Not attracted to the water NON--Not attracted to the water NON-

POLARPOLAR

Phospholipids can form BILAYERSPhospholipids can form BILAYERS-2 layers of phospholipids with-2 layers of phospholipids with hydrophobic tails protectedhydrophobic tails protected inside by the hydrophilicinside by the hydrophilic heads.heads.

The PHOSPHOLIPID BILAYER isThe PHOSPHOLIPID BILAYER is the basic structure of the basic structure of

membranes.membranes.


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Diagram representing the cell Diagram representing the cell membranemembrane

Remember the membrane is 7nm Remember the membrane is 7nm widewide


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Fluid mosaic modelFluid mosaic model

Cell membranes also contain proteins within the phospholipid bilayer.Cell membranes also contain proteins within the phospholipid bilayer.This ‘model’ for the structure of the membrane is called the:This ‘model’ for the structure of the membrane is called the:

FLUID MOSAIC MODELFLUID MOSAIC MODELFLUID- because individual phospholipids and proteins can move FLUID- because individual phospholipids and proteins can move

around freely within the layer, like it’s a liquid.around freely within the layer, like it’s a liquid.MOSAIC- because of the pattern produced by the scattered protein MOSAIC- because of the pattern produced by the scattered protein

molecules when the membrane is viewed from above.molecules when the membrane is viewed from above.


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Diagram of a cell membrane Diagram of a cell membrane


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TEM of freeze-fractured cell TEM of freeze-fractured cell membranemembrane. .

The fracture occurs The fracture occurs between the two between the two phospholipid phospholipid layers.layers.

You can clearly see You can clearly see the exposed the exposed proteins sticking proteins sticking out of the two out of the two layers.layers.

Individual Individual phospholipids are phospholipids are too small to see.too small to see.


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Cell Membranes from Opposing Cell Membranes from Opposing Neurons (TEM x436,740). Neurons (TEM x436,740).

} } Phospholipid Phospholipid BilayerBilayer

7nm wide7nm wide

1818AS Biology. Foundation. Cell AS Biology. Foundation. Cell membranes and Transportmembranes and Transport

Features of the fluid mosaic modelFeatures of the fluid mosaic model Double layer – BILAYER of phospholipids which can move about by

………………………… in their own ………………………. Phospholipid tails point inwards forming a ……. ………. …………………………

interior. The phospholipid heads point outwards facing the aqueous (water containing) medium surrounding the membrane.

Some phospholipids fatty acid tails are ……………………….. – straight so fit together tightly. Some are ………………………… – bent so fit together ……………………. The more unsaturated tails there are the more ……………… the membrane becomes. The lower the temp, the ……………….fluid.

Most protein molecules …………………. like icebergs in the layers, some are fixed to ………………………. inside the cell and don’t float.

Some proteins are embedded in the outer layer, some in the inner layer and some ………………… the two layers. Hydrophobic and Hyrdophilic parts of the protein molecules sit next to the …………………………… and ………………………….. portions of the ……………………………… of the membrane. This ensures the proteins stay in the membrane.

The membrane is ……nm thick on average. Some phospholipids have carbohydrates attached to them called-

……………………….. Some of the proteins have carbohydrates attached to them called–

…………………… The membrane also contains molecules of ………………………………..


Features of the fluid mosaic modelFeatures of the fluid mosaic model Double layer – BILAYER of phospholipids which can move about by

DIFFUSION in their own MONOLAYER Phospholipid tails point inwards forming a NON-POLAR HYDROPHOBIC

interior. The phospholipid heads point outwards facing the aqueous (water containing) medium surrounding the membrane.

Some phospholipids fatty acid tails are SATURATED – straight so fit together tightly. Some are UNSATURATED – bent so fit together loosely. The more unsaturated tails there are the more ‘fluid’ the membrane becomes. The lower the temp, the less fluid.

Most protein molecules float like icebergs in the layers, some are fixed to structures inside the cell and don’t float.

Some proteins are embedded in the outer layer, some in the inner layer and some span the two layers. Hydrophobic and Hyrdophilic parts of the protein molecules sit next to the Hydrophobic and Hydrophilic portions of the phospholids of the membrane. This ensures the proteins stay in the membrane.

The membrane is 7nm thick on average. Some phospholipids have carbohydrates attached to them – GLYCOLIPIDS Some of the proteins have carbohydrates attached to them –

GLYCOPROTEINS The membrane also contains molecules of CHOLESTEROL


Roles of components of cell membranesRoles of components of cell membranes

Using the following headings produce a table on A4 to summarise roles Using the following headings produce a table on A4 to summarise roles of t heof t he

different types of molecules found in the cell membrane. Try not to different types of molecules found in the cell membrane. Try not to copy, pickcopy, pick

out the relevant information and write it in note form You may want to out the relevant information and write it in note form You may want to use use

bullet points, different coloured pens etc basically whatever helps you bullet points, different coloured pens etc basically whatever helps you to remember them.to remember them.

There will be a short test on this next lesson! Use pages 53-54.There will be a short test on this next lesson! Use pages 53-54.

ComponentComponent Function Function

1.1. PhospholipidsPhospholipids

2.2. CholesterolCholesterol

3.3. ProteinsProteins

4.4. Glycolipids and GlycoproteinsGlycolipids and Glycoproteins


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SummarySummary Cell membranes have a basic structure composed of a PHOSPHOLIPID BILAYER.

Phospholipds have HYDROPHOBIC (non-polar) tails and HYDROPHILIC (polar) heads.

The best model of the cell membrane is called the FLUID MOSAIC MODEL

The average thickness of the membrane is 7nm.

The fatty acid tails of phospholipids can be SATURATED (straight) or UNSATURATED

(bent)

Proteins can float or be fixed and also have hydrophobic and hydrophilic portions.

Some proteins and phospholipids have carbohydrates attached to them to form

GLYCOPROTEINS AND GLYCOLIPIDS.

Phospholipids form the bilayer, act as barrier to most water soluble substances

Cholesterol regulates the fluidity of the membrane, gives mechanical stability and

help to prevent ions from passing through the membrane.

Proteins act as transport proteins to act as channels for substances to move into or

out of the cell. Some act as membrane enzymes and some have important roles in

membranes of organelles.

Glycolipids and Glycoproteins help to stabilise membrane structure, some act as

receptor molecules eg for hormones and neurotransmitters or as antigens for other

cells to recognise them.


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Movement of selected Movement of selected molecules across the cell molecules across the cell

membrane membrane


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Moving amoebaMoving amoeba

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AS Biology. Foundation. Cell membranes and Transport1 AS Biology FOUNDATION Chapter 4 CELL MEMBRANES and TRANSPORT Visit