2.4 Membranes 2.4 Membranes 2.4.1 2.4.1 Draw a diagram to show the fluid mosaic Draw a diagram to show the fluid mosaic model of a biological membrane. model of a biological membrane. (1) (1) The diagram should show the phospholipid The diagram should show the phospholipid bilayer, cholesterol, glycoproteins and bilayer, cholesterol, glycoproteins and integral and peripheral proteins. integral and peripheral proteins. Use the term plasma membrane not cell Use the term plasma membrane not cell surface membrane for the membrane surface membrane for the membrane surrounding the cytoplasm. surrounding the cytoplasm. Integral proteins are embedded in the Integral proteins are embedded in the phospholipid of the membrane whereas phospholipid of the membrane whereas peripheral proteins are attached to its peripheral proteins are attached to its surface. surface.
Transcript
2.4 Membranes2.4 Membranes
2.4.12.4.1Draw a diagram to show the fluid mosaic model Draw a diagram to show the fluid mosaic model
of a biological membrane. of a biological membrane. (1)(1) The diagram should show the phospholipid The diagram should show the phospholipid
bilayer, cholesterol, glycoproteins and integral bilayer, cholesterol, glycoproteins and integral and peripheral proteins. and peripheral proteins.
Use the term plasma membrane not cell Use the term plasma membrane not cell surface membrane for the membrane surface membrane for the membrane surrounding the cytoplasm. surrounding the cytoplasm.
Integral proteins are embedded in the Integral proteins are embedded in the phospholipid of the membrane whereas phospholipid of the membrane whereas peripheral proteins are attached to its surface. peripheral proteins are attached to its surface.
2.4 Membranes2.4 Membranes
2.4.22.4.2
Explain how the hydrophobic and Explain how the hydrophobic and hydrophilic properties of phospholipids hydrophilic properties of phospholipids help to maintain the structure of cell help to maintain the structure of cell membranes. (3)membranes. (3)
Hydrophobic – ‘afraid of water’Hydrophobic – ‘afraid of water’
cells cells Cell adhesion – Tight junctionsCell adhesion – Tight junctions channels for passive transport – channels for passive transport –
facilitated diffusion channelsfacilitated diffusion channels pumps for active transport.pumps for active transport.
Concept CheckConcept Check
Membranes organize cell activities. The proteins Membranes organize cell activities. The proteins imbedded in the membranes are essential to their function. imbedded in the membranes are essential to their function. These membrane proteins have properties that allow them These membrane proteins have properties that allow them to “float” in the membrane. Which of the following to “float” in the membrane. Which of the following describe those properties?describe those properties? The surface region of the protein in the interior of the membrane is The surface region of the protein in the interior of the membrane is
mostly hydrophobic.mostly hydrophobic. The surface region of the protein in the interior of the membrane is The surface region of the protein in the interior of the membrane is
mostly hydrophillic. mostly hydrophillic. The surface region exposed to the outer environment is hydrophobic. The surface region exposed to the outer environment is hydrophobic. The surface region exposed to the interior environment is The surface region exposed to the interior environment is
hydrophobic.hydrophobic.
AnswerAnswer
Membranes organize cell activities. The proteins imbedded Membranes organize cell activities. The proteins imbedded in the membranes are essential to their function. These in the membranes are essential to their function. These membrane proteins have properties that allow them to “float” membrane proteins have properties that allow them to “float” in the membrane. Which of the following describe those in the membrane. Which of the following describe those properties?properties? The surface region of the protein in the interior of the membrane is The surface region of the protein in the interior of the membrane is
mostly hydrophobic.mostly hydrophobic.
2.4 Membranes2.4 Membranes
2.4.42.4.4Define diffusionDefine diffusion (1) (1)Diffusion is the passive movement of particles from Diffusion is the passive movement of particles from
a region of high concentration to a region of low a region of high concentration to a region of low concentration (down a concentration gradient), concentration (down a concentration gradient), until there is an equal distribution.until there is an equal distribution.
Define osmosisDefine osmosis Osmosis is the passive movement of water Osmosis is the passive movement of water
molecules, across a partially permeable molecules, across a partially permeable membrane, from a region of lower solute membrane, from a region of lower solute concentration (high water concentration) to a concentration (high water concentration) to a region of higher solute concentration (low water region of higher solute concentration (low water concentration).concentration).
2.4 Membranes2.4 Membranes
2.4.52.4.5
Explain passive transport across membranes Explain passive transport across membranes in terms of diffusion.in terms of diffusion. (3)(3)
Requires no energyRequires no energy
Moves from down the concentration gradientMoves from down the concentration gradient
Some molecules pass through the membraneSome molecules pass through the membrane
Some molecules use channels for facilitated Some molecules use channels for facilitated diffusion diffusion
Passive transport is diffusion across a Passive transport is diffusion across a membranemembrane In passive transport, substances diffuse In passive transport, substances diffuse
through membranes without work by the cellthrough membranes without work by the cell Spreading from areas of high concentration to areas Spreading from areas of high concentration to areas
of low concentrationof low concentrationEquilibriumMembraneMolecules of dye
Equilibrium
Figure 5.14B
Figure 5.14A
Passive TransportPassive Transport
Small nonpolar molecules such as OSmall nonpolar molecules such as O22 and and COCO22
Diffuse easily across the phospholipid bilayer Diffuse easily across the phospholipid bilayer of a membraneof a membrane
Transport proteins may facilitate Transport proteins may facilitate diffusion across membranesdiffusion across membranes Many kinds of moleculesMany kinds of molecules
Do not diffuse freely across membranesDo not diffuse freely across membranes For these molecules, transport proteinsFor these molecules, transport proteins
Provide passage across membranes through a Provide passage across membranes through a process called facilitated diffusionprocess called facilitated diffusion
Figure 5.15
Solutemolecule
Transportprotein
Osmosis is the diffusion of water across a Osmosis is the diffusion of water across a membranemembrane In osmosisIn osmosis
Water travels from a solution of lower solute Water travels from a solution of lower solute concentration to one of higher solute concentrationconcentration to one of higher solute concentration
Figure 5.16
Lowerconcentration
of solute
Higherconcentration
of solute
Equalconcentration
of solute
H2OSolutemolecule
Selectivelypermeablemembrane
Watermolecule
Solute molecule withcluster of water molecules
Net flow of water
OsmosisOsmosis
Concept CheckConcept Check
This diagram represents osmosis This diagram represents osmosis of water across a semipermeable of water across a semipermeable membrane. The U-tube on the membrane. The U-tube on the right shows the results of the right shows the results of the osmosis. What could you do to osmosis. What could you do to level the solutions in the two level the solutions in the two sides of the right hand U-tube?sides of the right hand U-tube?
Add more water to the left hand Add more water to the left hand side.side.
Add more water to the right Add more water to the right hand side. hand side.
Add more solute to the left hand Add more solute to the left hand side. side.
Add more solute to the right Add more solute to the right hand side.hand side.
AnswerAnswer
This diagram represents osmosis This diagram represents osmosis of water across a semipermeable of water across a semipermeable membrane. The U-tube on the membrane. The U-tube on the right shows the results of the right shows the results of the osmosis. What could you do to osmosis. What could you do to level the solutions in the two level the solutions in the two sides of the right hand U-tube?sides of the right hand U-tube?
Add more solute to the left hand Add more solute to the left hand
side. side.
2.4 Membranes2.4 Membranes
2.4 Membranes2.4 Membranes
2.4.62.4.6Explain the role of protein pumps and ATP in Explain the role of protein pumps and ATP in
active transport across membranes.active transport across membranes. (3)(3)
Requires energy, in the form of ATP, or Requires energy, in the form of ATP, or adenosine triphosphateadenosine triphosphate
Molecules are ‘pumped’ across the membrane Molecules are ‘pumped’ across the membrane UP the concentration gradientUP the concentration gradient
Pumps fit specific moleculesPumps fit specific moleculesThe pump changes shape when ATP activates The pump changes shape when ATP activates
it, this moves the molecule across the it, this moves the molecule across the membranemembrane
Active TransportActive Transport
Active TransportActive Transport
2.4 Membranes2.4 Membranes
2.4.72.4.7
Explain how vesicles are used to transport Explain how vesicles are used to transport materials within a cell between the rough materials within a cell between the rough endoplasmic reticulum, Golgi apparatus endoplasmic reticulum, Golgi apparatus and plasma membrane. (3)and plasma membrane. (3)
2.4.82.4.8 Describe how the fluidity of the Describe how the fluidity of the membrane allows it to change shape, membrane allows it to change shape, break and reform during endocytosis and break and reform during endocytosis and exocytosis. (2)exocytosis. (2)
2.4 Membranes2.4 Membranes
Endocytosis – the mass movement INTO the cell Endocytosis – the mass movement INTO the cell by the membrane ‘pinching’ into a vacuoleby the membrane ‘pinching’ into a vacuole
Exocytosis – the mass movement OUT of the cell Exocytosis – the mass movement OUT of the cell by the fusion of a vacuole and the membraneby the fusion of a vacuole and the membrane
This is possible because the of the fluid This is possible because the of the fluid properties of the membrane (able to break properties of the membrane (able to break and reform easily, phospholipids not attached and reform easily, phospholipids not attached just attracted)just attracted)
ExocytosisExocytosis
EndocytosisEndocytosisendo- and exo-
-cytosis
Endocytosis can occur in three waysEndocytosis can occur in three ways PhagocytosisPhagocytosis PinocytosisPinocytosis Receptor-mediated endocytosisReceptor-mediated endocytosis
Faulty membranes can overload the Faulty membranes can overload the blood with cholesterolblood with cholesterol Harmful levels of cholesterolHarmful levels of cholesterol
Can accumulate in the blood if membranes Can accumulate in the blood if membranes lack cholesterol receptorslack cholesterol receptors
LDL particle
Protein
Phospholipid outer layer
CytoplasmReceptorprotein
Plasmamembrane
Vesicle
Cholesterol
Figure 5.20
Endocytosis and Endocytosis and ExocytosisExocytosis
