Download The Cell Membrane

The Cell Membrane
Function
 Regulates the movement of materials
from one environment to the other.
 Transports raw materials into the cell and
waste out of the cell.
 Prevents the entry of unwanted matter
and the escape of needed materials.
 Maintain a steady environment:
Homeostasis
Structure:
 Composed of a phospholipid bilayer with
a collage of many different proteins, lipids
and carbohydrates.
 A Phospholipid is composed of 1 glycerol
molecule, 2 fatty acids and 1 phosphate
group. This structure causes hydrophilic
and hydrophobic regions.
The Fluid-Mosaic
Membrane Model
 Membranes are not static; they have a fluid
consistency.
 Most membrane lipids and proteins can drift
about laterally in the plane of the membrane.
 Cholesterol enhances membrane fluidity,
allows animal membranes to function in a wide
range of temperatures and also makes the
membrane less permeable to biological
molecules.
Membrane Proteins:
Two Types:
 Integral: Proteins that insert into the
membrane (transmembrane proteins)
 Peripheral: Proteins attached to the surface
of the cell membrane.
Function:
 Transportation
 Enzymes
 Receptor sites
 Cell adhesion
 Attachment to the cytoskeleton
Carbohydrates:
 Usually branched molecules of 15 or less
sugar units.
 Some are bonded to lipids: Glycolipids.
 Most are bonded to proteins:
Glycoproteins.
 Function: Cell-cell recognition.
Construction of a Cell
Membrane
Copy the link below to create your own cell
membrane.
http://www.wisconline.com/objects/index_tj.asp?objID=A
P1101
Through the Cell
Membrane
1.
2.
3.
4.
5.
Diffusion
Osmosis
Facilitated Diffusion
Active Transport
Bulk Transport
1. Diffusion:





Passive movement of molecules from a region
of high concentration to a region of low
concentration.
(Concentration gradient is the difference in
concentration between the two regions)
Small, uncharged molecules like O2, CO2 and
H2O can move easily through the membrane.
Works well over short distances. Once
molecules enter the cell the rate of diffusion
slows.
Limits cell size.
Passive Transport
2. Osmosis
 Diffusion of the solvent across a semi-permeable
membrane separating two solutions. (Diffusion of
water)
 Water molecules move from a region of high
concentration to a region of low concentration.
 Direction depends on the relative concentration of
water molecules on either side of the cell membrane.
 Isotonic: Water inside the cell equals the water outside
the cell and equal amounts of water move in and out of
the cell.
 Hypotonic: Water outside the cell is greater than that
inside the cell, water moves into the cell, may cause
cell to burst (lysis)
 Hypertonic: Water inside the cell is greater than
outside. Water moves out of the cell, may cause the
cell to shrink (plasmolysis)
Osmosis: Hypotonic
3. Facilitated Diffusion
 Assists with the movement of large molecules
like glucose.
 Passive movement of a substance into or out
of the cell by means of carrier proteins or
channel proteins.
 Moves molecules from high to low regions of
concentration.
 Carrier proteins: Transports non-charged
molecules with a specific shape.
 Channel proteins: Tunnel shape that
transports small charged molecules.
4. Active Transport
 The process of moving substances against their
concentration gradients. Requires energy.
 Examples:
 Kidney cells pump glucose and amino acids out of the
urine and back into the blood.
 Intestinal cells pump in nutrients from the gut.
 Root cells pump in nutrients from the soil.
 Gill cells in fish pump out sodium ions.
 Active Transport Pump:
 Sodium-potassium pump
 3 sodium ions inside the cell and 2 potassium ions
outside the cell bind to the pump.
 This allows the release of energy from ATP and
causes the protein complex to change shape.
 The change in shape allow the Na + and K+ ions to
move across and be released.
Active Transport Pump
5. Bulk Transport
1. Endocytosis: The cell membrane folds
inward, traps and encloses a small amount of
matter from the extracellular fluid. 3 types:
Endocytosis
 Pinocytosis: The intake of a small droplet of
extracellular fluid. This occurs in nearly all cell
types.
 Phagocytosis: The intake of a large droplet of
extracellular fluid. This occurs in specialized cells.
 Receptor-assisted endocytosis: The intake of
specific molecules that attach to special proteins in
the cell membrane. These proteins are uniquely
shaped to fit the shape of a specific molecule.
Bulk Transport
2. Exocytosis: The reverse of endocytosis: A
vesicle from inside the cell moves to the cell
membrane. The vesicle fuses to the membrane
and the contents are secreted