Transcript Cell Transport

Cell Transport
• Moving things into and out of the cell
through the cell membrane to
maintain balance (homeostasis)
• Passive:
– Doesn’t take any energy from the cell
– Just happens (kinetic energy of
molecules)
• Active:
– Uses the cell’s energy, from mitochondria
– ATP (Adenosine TriPhosphate)
Cell Memebrane
• Phospholipid Bilayer
– 2 layers, back to back, of molecules of fat
called phospholipids
• Fluid Mosaic
– Other molecules, too, like proteins, but
they don’t just sit there, they move
around
• Selectively permeable
– Not just anything can pass through
Cell membrane
Diffusion
• Molecules simply move from an
area of higher concentration to
lower (with concentration gradient)
• Because of the molecules’ kinetic
energy (passive)
• Will stop when reach equilibrium
(equal concentration)
• Molecules still move, but for each one
that moves in to the cell, one moves
out (no net movement)
Diffusion across cell
membrane
• Happens only for very small particles
(salt, etc.)
• Move between phospholipid
molecules of the bilayer
• Or for molecules that are nonpolar
(hydrophobic) and dissolve into the
space between the two layers of the
cell membrane, but not in water
Facilitated diffusion
• For molecules that are too big to get
in (e.g. sugar), or have charges
(ions)
• Proteins in the cell membrane will
chemically bind to the molecule.
(specific…only 1 molecule per
protein…like a lock and key)
• The protein will then change shape
and the molecule will move in or
out of the cell.
• Takes no energy (passive)
Facilitated diffusion
•Note: each protein is specific for one
molecule, but there are many different
proteins in each cell membrane
Osmosis
• Special kind of diffusion (passive)
• Only for water across the
membrane
• Water can move against its
concentration gradient, that is
water can move from low water
to high water concentration
• Water moves to “water down”
whatever is most concentrated.
Osmosis
• If the cell has more “stuff”
dissolved outside than inside, it
is in a hypertonic environment
• It will try to “water down” the
environment to make it less
harsh
• Water leaves the cell, the cell
shrinks (plasmolysis)
• http://www.youtube.com/watch?
v=gWkcFU-hHUk&feature=related
Osmosis
• If the cell has more “stuff” dissolved
inside than outside, it is in a
hypotonic environment
• It will try to “water down” the inside to
make it less harsh
• Water enters the cell, the cell grows
• If it gets too big, it explodes (cytolysis)
• http://vimeo.com/2726364
Osmosis
• If the cell has equal amounts of
“stuff” dissolved inside and out,
it is in an isotonic environment
• Water molecules will move both in
and out of the cell equally, so
there is no net movement of
water
• Notes: water still moves in and out in
hypertonic and hypotonic
solutions, but the net movement is
in one direction
Equilibrium
• Passive transport will continue
until equal concentrations are
reached in and out of the cell
(equilibrium).
• Molecules still move back and
forth across the membrane,
but do so at equal rates
• No net (total) movement of
molecules, though
Active Transport
• Sometimes cell wants higher or
lower concentrations (not
equilibrium)
• Have to use the cell’s energy (ATP
adenosine triphosphate)
• Moves against concentration, i.e.
from low to high concentration
• Moves large molecules or large
amounts of molecules
Protein Pumps
• Energy changes shape of the
protein to move things in/out
of the cell
• Is specific…each protein can only
chemically bind with one
molecule, but there are many
different proteins in the cell
membrane (like a lock and key)
• Na+ K + pump
Protein pumps
• 3 sodiums are taken out of the cell
and 2 potassiums brought in using
ATP.
Transport by vesicle
• Moves large molecules or large
quantities of something into
and out of the cell
• Into the cell is called endocytosis
– Pinocytosis: water/liquid moves
– Phagocytosis: solids move
• Out of the cell is called
exocytosis (e.g. products from
Golgi Apparatus)
Endocytosis
•Note part of cell membrane makes the
vesicle and is now inside the cell!
•http://www.youtube.com/watch?v=W6rnhiMxt
KU
Exocytosis
•Note the vesicle fuses with the cell membrane
and is now part of it!
•http://www.youtube.com/watch?v=U9pvm_4bHg
ATP
•Adenosine
Triphosphate
•Adenosine
Diphosphate
•ATP
•ADP + P +
energy