AS Biology cell membranes: organells.ppt

A brief description of the functions of organells of the cell.

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AS BiologyAS Biology
FOUNDATIONFOUNDATION
Chapter 4Chapter 4
CELL MEMBRANESCELL MEMBRANES
andand
TRANSPORTTRANSPORT

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The CellThe Cell

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Learning ObjectivesLearning Objectives
1.1.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 within Outline the roles of the plasma membrane, and the roles of membranes within
cells.cells.
4.4.Describe and explain how molecules can get in and out of cells (cross cell Describe and explain how molecules can get in and out of cells (cross cell
membranes) by the processes of diffusion, facilitated diffusion, osmosis, membranes) by the processes of diffusion, facilitated diffusion, osmosis,
active transport, endocytosis and exocytosis.active transport, endocytosis and exocytosis.
5.5.Describe the effects on animal and plant cells of immersion in solutions of Describe the effects on animal and plant cells of immersion in solutions of
different water potential.different water potential.
6.6.Describe the features of the gaseous exchange surface of mammalian lung.Describe the features of the gaseous exchange surface of mammalian lung.
7.7.Describe the features of root hairs that enable the uptake of ions by active Describe the features of root hairs that enable the uptake of ions by active
transport.transport.

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Key words you should knowKey words you should know
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Phospholipids Phospholipids SolutionSolution PinocytosisPinocytosis
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PolarPolar SoluteSolute MicropinocytosisMicropinocytosis
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HydrophilicHydrophilic SolventSolvent ExocytosisExocytosis
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HydrophobicHydrophobic Partially permeablePartially permeable Gaseous exchangeGaseous exchange
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MicellesMicelles Water potentialWater potential AlveoliAlveoli
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Phospholipid bilayerPhospholipid bilayer Solute PotentialSolute Potential Root hairRoot hair
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Fluid mosaic modelFluid mosaic modelPressure PotentialPressure Potential Surface areaSurface area
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GlycoproteinsGlycoproteins TurgidTurgid EpidermisEpidermis
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GlycolipidsGlycolipids PlasmolysisPlasmolysis Passive transportPassive transport
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CholesterolCholesterol PlasmolysedPlasmolysed
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ProteinsProteins Incipient plasmolysisIncipient plasmolysis
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Transport proteinsTransport proteinsActive transportActive transport
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EnzymesEnzymes Carrier proteinCarrier protein
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Receptor moleculesReceptor moleculesBulk transportBulk transport
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DiffusionDiffusion EndocytosisEndocytosis
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Concentration gradientConcentration gradient PhagocytosisPhagocytosis
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Facilitated diffusionFacilitated diffusion PhagocytesPhagocytes
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OsmosisOsmosis Phagocytic vacuolesPhagocytic vacuoles

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Cell membraneCell membrane
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All living things are surrounded by a membrane.All living things are surrounded by a membrane.
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A cell membrane is also known as plasma membrane.A cell membrane is also known as plasma membrane.
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Controls exchange of materials such as nutrients and Controls exchange of materials such as nutrients and
waste between cells and their environment.waste between cells and their environment.

Has other important functions for example to enable Has other important functions for example to enable
cells to receive hormones.cells to receive hormones.

To understand the function of anything in biology, you To understand the function of anything in biology, you
must study the structure first!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 membrane cell membrane
7nm wide7nm wide
Cell membrane Cell membrane {{
Nerve cellNerve cell
Nerve cellNerve cell
Gap between cellsGap between cells

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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 the -Not attracted to the
waterwater
called NON-POLARcalled NON-POLAR
Cell membranes are made of Cell membranes are made of
PHOSPHOLIPIDsPHOSPHOLIPIDs
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 normally found on a (PO4-) replaces one of the three fatty acids normally found on a
lipid. The addition of this group makes a polar "head" and two lipid. The addition of this group makes a polar "head" and two
nonpolar "tails".nonpolar "tails".

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A phospholipidA phospholipid
HYDROPHILIC HEADHYDROPHILIC HEAD
At 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 end bonded oxygens. The atoms at this end
of the molecule are not shared equally. of the molecule are not shared equally.
This end of the molecule has a charge This end of the molecule has a charge
and is attracted to water. It is POLARand is attracted to water. It is POLAR
HYDROPHOBIC TAILSHYDROPHOBIC TAILS
The two long chains coming off of the The two long chains coming off of the
bottom of this molecule are made up of bottom of this molecule are made up of
carbon and hydrogen. Because both of carbon and hydrogen. Because both of
these elements share their electrons these elements share their electrons
evenly these chains have no charge. They evenly these chains have no charge. They
are NON POLAR. Molecules with no are NON POLAR. Molecules with no
charge are not attracted to water; as a charge are not attracted to water; as a
result water molecules tend to push result water molecules tend to push
them out of the way as they are them out of the way as they are
attracted to each other. This causes attracted to each other. This causes
molecules with no charge not to dissolve molecules with no charge not to dissolve
in water. in water. 3D model of a 3D model of a
PhospholipidPhospholipid

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A Phospholipid BilayerA Phospholipid Bilayer
Phospholipids can form: Phospholipids can form:
BILAYERSBILAYERS
-2 layers of -2 layers of
phospholipids withphospholipids with
hydrophobic tails hydrophobic tails
protected inside by the protected inside by the
hydrophilic heads.hydrophilic heads.
The PHOSPHOLIPIDThe PHOSPHOLIPID
BILAYER is the basicBILAYER is the basic
structure of membranes.structure of membranes.

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Structure of the cell membraneStructure of the cell membrane
PhospholipidsPhospholipids
Cell membranes are made mainly of Cell membranes are made mainly of
phospholipids. They have:phospholipids. They have:
HYDROPHILIC heads (water liking)HYDROPHILIC heads (water liking)
-Attracted to the water POLAR-Attracted to the water POLAR
HYDROPHOBIC tails (water fearing)HYDROPHOBIC tails (water 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 membranes.the basic structure of membranes.

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Diagram representing the cell membraneDiagram representing the cell membrane
Remember the membrane is 7nm wideRemember the membrane is 7nm wide

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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 MODEL
FLUID- because individual phospholipids and proteins can move around FLUID- because individual phospholipids and proteins can move around
freely within the layer, like it’s a liquid.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 layers.phospholipid layers.
You can clearly see the You can clearly see the
exposed proteins exposed proteins
sticking out of the sticking out of the
two layers.two layers.
Individual phospholipids Individual phospholipids
are too small to see.are 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 BilayerPhospholipid Bilayer
7nm wide7nm wide

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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 ………………………………..

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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

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Roles of components of cell membranesRoles of components of cell membranes
Using the following headings produce a table on A4 to summarise roles of t heUsing the following headings produce a table on A4 to summarise roles of t he
different types of molecules found in the cell membrane. Try not to copy, pickdifferent types of molecules found in the cell membrane. Try not to copy, pick
out the relevant information and write it in note form You may want to use out the relevant information and write it in note form You may want to use
bullet points, different coloured pens etc basically whatever helps you to bullet points, different coloured pens etc basically whatever helps you to
remember them.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 molecules Movement of selected molecules
across the cell membrane across the cell membrane

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Moving amoebaMoving amoeba

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