The cell membrane function

The cell membrane function

1. The Cell Membrane The Cell Membrane
FunctionsFunctions

2. 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

3. Structure:Structure:
Composed of a phospholipid bilayer with Composed of a phospholipid bilayer with
a collage of many different proteins, a collage of many different proteins,
lipids and carbohydrates.lipids 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.

4. Phospholipid bilayerPhospholipid bilayer
polar
hydrophilic
heads
nonpolar
hydrophobic
tails
polar
hydrophilic
heads

6. 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.

7. Membrane Proteins:Membrane Proteins:
Two Types:Two Types:
Integral:Integral: Proteins that insert into the Proteins that insert into the
membrane (transmembrane proteins)membrane (transmembrane proteins)
Peripheral:Peripheral: Proteins attached to the surface Proteins attached to the surface
of the cell membrane.of the cell membrane.
Function:Function:
TransportationTransportation
EnzymesEnzymes
Receptor sitesReceptor sites
Cell adhesionCell adhesion
Attachment to the cytoskeletonAttachment to the cytoskeleton

8. 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.

9. Membrane Membrane
carbohydrates carbohydrates
Play a key role in Play a key role in cell-cell recognitioncell-cell recognition
ability of a cell to distinguish one cell from ability of a cell to distinguish one cell from
anotheranother
antigensantigens
important in organ & important in organ &
tissue developmenttissue development
basis for rejection of basis for rejection of
foreign cells by foreign cells by
immune systemimmune system

11. Membrane is a collage of proteins & other Membrane is a collage of proteins & other
molecules embedded in the fluid matrix of the molecules embedded in the fluid matrix of the
lipid bilayerlipid bilayer
Extracellular fluid
Cholesterol
Cytoplasm
Glycolipid
Transmembrane
proteins
Filaments of
cytoskeleton
Peripheral
protein
Glycoprotein
Phospholipids

12. 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

13. 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 O
22, CO, CO
22 and and
HH
22O 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.

14. Move from Move from HIGHHIGH to to LOWLOW concentration concentration
““passive transport”passive transport”
no energy neededno energy needed
diffusion osmosis
movement of water

15. 1515
AquaporinsAquaporins
Water ChannelsWater Channels
Protein pores used during OSMOSISProtein pores used during OSMOSIS
WATER
MOLECULES
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16. 1616
Isotonic Solution
NO NET MOVEMENT OF
H
2
O (equal amounts
entering & leaving)
Hypotonic
Solution
CYTOLYSIS
Hypertonic
Solution
PLASMOLYSIS
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17. 1717
Cytolysis & Cytolysis &
PlasmolysisPlasmolysis
Cytolysis Plasmolysi
s
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18. 1818
Three Forms of Transport Across the MembraneThree Forms of Transport Across the Membrane
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19. 2. Osmosis2. Osmosis
Diffusion of the solvent across a semi-permeable Diffusion of the solvent across a semi-permeable
membrane separating two solutions. (Diffusion of membrane separating two solutions. (Diffusion of
water)water)
Water molecules move from a region of high Water molecules move from a region of high
concentration to a region of low concentration.concentration to a region of low concentration.
Direction depends on the relative concentration of Direction depends on the relative concentration of
water molecules on either side of the cell membrane.water molecules on either side of the cell membrane.
Isotonic:Isotonic: Water inside the cell equals the water Water inside the cell equals the water
outside the cell and equal amounts of water move in outside the cell and equal amounts of water move in
and out of the cell.and out of the cell.
Hypotonic:Hypotonic: Water outside the cell is greater than that Water outside the cell is greater than that
inside the cell, water moves into the cell, may cause inside the cell, water moves into the cell, may cause
cell to burst (lysis)cell to burst (lysis)
Hypertonic:Hypertonic: Water inside the cell is greater than Water inside the cell is greater than
outside. Water moves out of the cell, may cause the outside. Water moves out of the cell, may cause the
cell to shrink (plasmolysis)cell to shrink (plasmolysis)

21. Osmosis: HypotonicOsmosis: Hypotonic

22. 3. Facilitated Diffusion3. Facilitated Diffusion
Assists with the movement of large molecules Assists with the movement of large molecules
like glucose.like glucose.
PassivePassive movement of a substance into or out movement of a substance into or out
of the cell by means of carrier proteins or of the cell by means of carrier proteins or
channel proteins.channel proteins.
Moves molecules from high to low regions of Moves molecules from high to low regions of
concentration.concentration.
Carrier proteins:Carrier proteins: Transports non-charged Transports non-charged
molecules with a specific shape.molecules with a specific shape.
Channel proteins:Channel proteins: Tunnel shape that Tunnel shape that
transports small charged molecules.transports small charged molecules.

23. 4. Active Transport4. Active Transport
The process of moving substances against their The process of moving substances against their
concentration gradients. Requires energy.concentration gradients. Requires energy.
Examples:Examples:
Kidney cells pump glucose and amino acids out of the Kidney cells pump glucose and amino acids out of the
urine and back into the blood.urine and back into the blood.
Intestinal cells pump in nutrients from the gut.Intestinal cells pump in nutrients from the gut.
Root cells pump in nutrients from the soil.Root cells pump in nutrients from the soil.
Gill cells in fish pump out sodium ions.Gill cells in fish pump out sodium ions.
Active Transport Pump:Active Transport Pump:
Sodium-potassium pumpSodium-potassium pump
3 sodium ions inside the cell and 2 potassium ions 3 sodium ions inside the cell and 2 potassium ions
outside the cell bind to the pump.outside the cell bind to the pump.
This allows the release of energy from ATP and This allows the release of energy from ATP and
causes the protein complex to change shape.causes the protein complex to change shape.
The change in shape allow the Na + and K+ ions to The change in shape allow the Na + and K+ ions to
move across and be released.move across and be released.

24. Active Transport PumpActive Transport Pump

25. 2525
Active Active
transporttransport
Examples: Pumping Examples: Pumping
NaNa
++
(sodium ions) out (sodium ions) out
and Kand K
++
(potassium (potassium
ions) in against ions) in against
strong concentration strong concentration
gradientsgradients..
Called Na+-K+ PumpCalled Na+-K+ Pump
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26. 2626
Sodium-Potassium PumpSodium-Potassium Pump
3 Na+ pumped in for every 2 K+ pumped
out; creates a membrane potential

27. 5. Bulk Transport5. Bulk Transport
1. Endocytosis:1. Endocytosis: The cell membrane folds The cell membrane folds
inward, traps and encloses a small amount of inward, traps and encloses a small amount of
matter from the extracellular fluid. 3 types:matter from the extracellular fluid. 3 types:

28. EndocytosisEndocytosis
Pinocytosis: Pinocytosis: The intake of a small droplet of The intake of a small droplet of
extracellular fluid. This occurs in nearly all cell types.extracellular fluid. This occurs in nearly all cell types.
Phagocytosis:Phagocytosis: The intake of a large droplet of The intake of a large droplet of
extracellular fluid. This occurs in specialized cells.extracellular fluid. This occurs in specialized cells.
Receptor-assisted endocytosis:Receptor-assisted endocytosis: The intake of The intake of
specific molecules that attach to special proteins in specific molecules that attach to special proteins in
the cell membrane. These proteins are uniquely the cell membrane. These proteins are uniquely
shaped to fit the shape of a specific molecule.shaped to fit the shape of a specific molecule.

29. Bulk TransportBulk Transport
2. Exocytosis:2. Exocytosis: The reverse of endocytosis: A The reverse of endocytosis: A
vesicle from inside the cell moves to the cell vesicle from inside the cell moves to the cell
membrane. The vesicle fuses to the membrane membrane. The vesicle fuses to the membrane
and the contents are secreted and the contents are secreted