Transcript on inside of cell membrane

Homeostasis
• Enough but
not too
much
A State of
Balance
"To stay alive, you have to be able to
hold out against equilibrium, maintain
imbalance, bank
against entropy, and you can only
transact this business with
membranes in our kind of world."
- Lewis Thomas in The Lives of a Cell
(1974)
Electron Micrograph of a
Cell Membrane showing
the Phospholipid bilayer
Cell membrane
Cell Membranes
• Are not solid
• Fluid Mosaic Model -A cell membrane
is made of many small pieces that are
moving
• The pieces stay together because they:
A. Are water loving (hydrophilic) or
B. Are water hating (hydrophobic)
movie
Phospholipids
Head of phospholipids
love
water
•Tails are two fatty acids
•Fats do not mix
with water
•Tails hate water.
The Phospholipids form a
bilayer
(the environment outside the Cell Is mostly water)
Thus, the heads which love water are attracted to the water
on the inside and outside of the cell
And the tails which hate water, stay inside away from water
(the cytosol inside the cell is mostly water)
Other structures found in Cell
Membrane
Carbohydrate Markers on outside of cell (help
Cells recognize each other)
Protein
Protein
Protein
Some proteins go from one side of the membrane
Cytoskeleton
(microtubules
and Microfilaments)
to the other side
of the membrane
on inside of cell membrane (provide support)
Some proteins go only part way through the membrane
Small uncharged molecules can pass
easily between the phospholipids.
O2
Na+
CO2 O2 CO2 O2
(outside the cell)
CO2
O2
CO2
Na+
Na+
O2
Na+
Na+
Na+
Na+
CO2
O2
CO2
O2
O2
Na+
CO2 O
2
CO2
Na+
Inside the cell
Some molecules pass through transport
(or Carrier) proteins
O2
Therefore a cell membrane is like a
fence with some molecules passing
between the rails that make up the
fence and some moving through the
gate.
Passive Transport
• movement of molecules across a
membrane without the use of chemical
energy.
Diffusion and osmosis
are examples of passive transport.
Diffusion-
video
video
Passive transport
process by which molecules move from one place to
another
Molecules diffuse from areas of higher concentration
to areas of lower concentration
until equilibrium is reached.
Each substance diffuses down its own
concentration gradient, independent of
the concentration gradients of other
substances
Animation lung cells
Cell Respires
Cell in pond water
CO2
O2
O2
CO2
O2
CO2
O2
CO
O2
CO
O22
CO2
CO
O2 2
2
O2
O2
CO2
CO2
O2 2
CO
O2
CO2
CO2
CO
O22
CO2
O2
O2
O2
CO2
O2
CO2
CO2
In Respiration, O2 is used up and CO2 is produced.
Thus, the balance in the cell changes.
Molecules move from higher
concentration to lower concentration
O2
CO2
O2
O2
O2 CO2 CO2
O2
O2
CO2
O2 CO2
CO2
CO2
O2
CO2
CO2
O2
O2
O2
O2
CO2
CO2
CO2
O2
CO2
CO2
O2
O2
CO2
CO2
CO2
CO2
O2
O2
O2
CO2
O2
CO2
Thus, Oxygen
enters the cell
CO2
O2
O2
And Carbon dioxide
Exits the cell
video
Facilitated Diffusion video
• the diffusion of molecules across cell
membranes through protein channels.
video
video
Osmosis- diffusion of water
through a semi-permeable
membrane.
Solution
• Made of:
Solvent- the dissolving substance
Solute- the substance that is dissolved
in the solvent
•The solution with the higher
concentration of solutes is
hypertonic. video
elodea
Water will leave the cell
H2O = 96 %
Solute = 4 %
H2O = 90%
Solute = 10%
More solute outside the cell
Figure 36.7 A watered Impatiens
plant regains its turgor
Venus fly trap
animation
– The solution with the lower
concentration of solutes is
hypotonic.
video
Water will enter the cell
H2O = 95 %
Solute = 5 %
H2O = 98 %
Solute = 2 %
Less solute outside the cell
Contractile Vacuole- cell in
hypotonic solution
Lower concentration of water in cell
Higher concentration of water
outside cell – water enters cell
Cytolysis of a Red Blood Cell in
Distilled Water (100% water)
http://www.usd.edu/~bgoodman/Osmos.htm
– Solutions with equal solute
concentrations are isotonic.
video
Water will enter
and leave at same rate
H2O = 90 %
Solute = 10 %
H2O = 90 %
Solute = 10 %
Equal amounts of solute
inside and outside the cell
Active transport: movement of
molecules against a concentration gradient.
Active transport -ATP Requires Energy.
Active Transport uses energy to
move molecules where they DON’T
want to go: against a
concentration gradient!
• Most nutrients are scarcer outside of cells
than inside of cells! Therefore diffusion will
not work to bring these nutrients inside!
Proteins, fats, sugars, ribosomes, ATP,
and other molecules would come pouring
OUT of cells if there was no way to force
them to stay or pack more inside the cell.
Video ATP
video
Endocytosis
Phagocytosis vs Pinocytosis
• The “cell drinking” of
material by the cell
Phagocytosis takes in solid particles Pinocytosis takes in
liquids
http://www.cells.de/cellseng/medienarchiv/archiv/bp1c1562d/1562_a3
3.htm
Phagocytosis
Click here for movie phagocytosis
Exocytosis
Enzymes overcome “activation energy”
Enzymes give an extra
push to reactions that don’t
require energy to finish.
Enzymes are facilitators:
they get all the reactants
together on the enzyme’s
surface so they can react.
Click here for turgid movie
Click here for plasmolysis movie
• Turgor Pressure- Water
enters the cell, fills the Central
Vacuole and gives plant cell
internal pressure.
Plasmolysis - water leaves cell,
turgor pressure is lost, cell wilts.
Cytolysis
• bursting of cells by water pressure.
• Animal cells do not have cell walls, so
turgor pressure cannot build up –
• Thus, cells burst.
Types of Transport
Cells in Isotonic Solutions
Cells in Hypertonic Solution
Cells in a Hypotonic Solution
Cytolysed